Scatter, Adapt, and Remember: How Humans Will Survive a Mass Extinction

THE LONG-TERM GOAL for Homo sapiens as a species right now should be to survive for at least another million years. It’s not much to ask. As we know, a few species have survived for billions of years, and many have survived for tens of millions. Our ancient ancestors started exploring the world beyond Africa over a million years ago, and so it seems fitting to pick the next million years as the first distant horizon where we’ll set our sights. We’ve already talked about how we can start this journey by building cities that are safer and more sustainable. Eventually, however, we’re going to build cities on the Moon and other planets. Our future is among the stars, as the science-fiction author Octavia Butler suggests. But long before we have the technologies to get there, our survival will depend on looking at Earth from the perspective of extraterrestrials.

Imagine we’re on an interstellar voyage and we encounter an Earthlike planet. As we survey it from orbit, we discover that this planet is full of life, and covered with sprawling artificial structures built by a scientifically advanced civilization. Seeing those, most of us would say the planet is controlled by a group of intelligent beings. That’s the extraterrestrial perspective. Right now, we’re stuck in the terrestrial perspective, where we do not really regard ourselves as “controlling” the Earth. Nor do we see ourselves as one group. From space we might look like a unified civilization of clever monkeys who hang out together building towers, but down on Earth we are Russians, Nigerians, Brazilians, and many other identities that divide us. Our differences aren’t always a problem. But they have so far prevented us from coming up with a global solution to maintaining the Earth’s resources. We won’t make it into the far future unless we start banding together as a species to control the Earth in a way we never have before.

When I say “control the Earth,” I don’t mean that we’ll all shake our fists at the sky and declare ourselves masters of everything. As entertaining as that would be, I’m talking about something a bit less grandiose. We simply need to take responsibility for something that’s been true for centuries: Human beings control what happens to most ecosystems on the planet. We’re an invasive species, and we’ve turned wild prairies into farms, deserts into cities, and oceans into shipping lanes studded with oil wells. There is also overwhelming evidence that our habit of burning fossil fuels has changed the molecular composition of the air we breathe, pushing us in the direction of a greenhouse planet. More than at any other time in history, humans control the environment. Still, our environment is going to change disastrously at some point, whether it’s heated by our carbon emissions from fossil fuels or cooled by megavolcano eruptions.

Our first priority in the near future must be to control our carbon output. I cannot emphasize this enough. As environmental writers like Bill McKibben and Mark Hertsgaard have argued, our fossil-fuel emissions are heating up the planet, and we can prevent this situation from becoming worse by using green sources of energy. Maggie Koerth-Baker points out in Before the Lights Go Out: Conquering the Energy Crisis Before It Conquers Us that we already have several types of sustainable energy to choose from, including solar and wind. Government representatives who attend the annual U.N. Climate Change Conferences are also coming up with strategies to encourage countries to curb fossil-fuel use, proposing everything from carbon taxes to emissions regulations.

The problem is that our climate has already been permanently changed for the next millennium, as the geobiologist Roger Summons explained in part one of this book. To prevent the planet from becoming uninhabitable, we’ll have to take our control of the environment a step further and become geoengineers, or people who use technology to shape geological processes. Though “geoengineering” is the proper term here, I used the word “terraforming” in the title of this chapter because it refers to making other planets more comfortable for humans. Earth has been many planets over its history. As geoengineers, we aren’t going to “heal” the Earth, or return it to a prehuman “state of nature.” That would mean submitting ourselves to the vicissitudes of the planet’s carbon cycles, which have already caused several mass extinctions. What we need to do is actually quite unnatural: we must prevent the Earth from going through its periodic transformation into a greenhouse that is inhospitable to humans and the food webs where we evolved. Put another way, we need to adapt the planet to suit humanity.

Over the coming centuries, we’ll need to take measures more drastic than cutting back on fossil-fuel use and ramping up the deployment of alternative energies. Eventually we’ll have to “hack the planet,” as they say in science-fiction movies. And we’ll do that in part by re-creating great planetary disasters from history.

Blocking the Sun

To make Earth more human-friendly, our geoengineering projects will need to cool the planet down and remove carbon dioxide from the atmosphere. These projects fall into two categories. The first, called solar management, would reduce the sunlight that warms the planet. The second, called carbon-dioxide removal, does exactly what it sounds like. Futurist Jamais Cascio, author of Hacking the Earth: Understanding the Consequences of Geoengineering, predicts that we’ll see an attempt to initiate a major geoengineering project in the next 10 years, and it will probably be solar management. “It’s a faster effect and tends to be relatively cheap, and some estimates are in the billion-dollar range,” he said. “It’s cheap enough that a small country or a rich guy with a hero complex who wants to save the world could do it.” Indeed, one solar-management project is already under way, albeit inadvertently. Evidence suggests that sulfur-laced aerosol exhaust emitted by cargo ships on the ocean changes the structure of high clouds, making them more reflective and possibly cooling temperatures over the water. Some solar-management plans take note of this discovery, and propose that we fill the oceans with ships spraying aerosols high into the air. But other strategies are more radical.

To find out how we’d shield our planet from sunlight, I visited the University of Oxford, winding my way through the city’s maze of pale gold spires and stone alleys to find an enclave of would-be geoengineers. Few deliberate geoengineering projects have been tried to date, but the mandate of the future-focused Oxford Martin School is to tackle scientific problems that will become important over the next century. The center is helping invent a field of science that doesn’t properly exist yet—but that will soon become critically important. One of its researchers is Simon Driscoll, a young geophysicist who divides his time between studying historic volcanic eruptions and figuring out how geoengineers could duplicate the effects of a volcano in the Earth’s atmosphere without actually blowing anything up.

Driscoll told me what volcanoes do to the atmosphere while cobbling together cups of tea in the cluttered atmospheric-physics department kitchen. Along with all the flaming lava, they emit tiny airborne particles called aerosols, which are trapped by the Earth’s atmosphere. He cupped his hands into a half sphere over the steam erupting from our mugs of tea, pantomiming the layers of Earth’s atmosphere trapping aerosols. Soot, sulfuric acid mixed with water, and other particles erupt from the volcano, shoot far above the breathable part of our atmosphere but remain hanging somewhere above the clouds, scattering solar radiation back into space. With less sunlight hitting the Earth’s surface, the climate cools. This is exactly what happened after the famous eruption of Krakatoa in the late 19th century. The eruption was so enormous that it sent sulfur-laced particles high into the stratosphere, a layer of atmosphere that sits between ten and forty-eight kilometers above the planet, where they reflected enough sunlight to lower global temperatures by 2.2 degrees Fahrenheit on average. The particles altered weather patterns for several years.

Driscoll drew a model of the upper atmosphere on a whiteboard. “Here’s the troposphere,” he said, drawing an arc. Above that he drew another arc for the tropopause, which sits between the troposphere and the next arc, the stratosphere. Most planes fly roughly in the upper troposphere, occasionally entering the stratosphere. To cool the planet, Driscoll explained, we’d want to inject reflective particles into the stratosphere, because it’s too high for rain to wash them out. These particles might remain floating in the stratosphere for up to two years, reflecting the light and preventing the sun from heating up the lower levels of the atmosphere, where we live. Driscoll’s passion is in creating computer models of how the climate has responded to past eruptions. He then uses those models to predict the outcomes of geoengineering projects.

The Harvard physicist and public-policy professor David Keith has suggested that we could engineer particles into tiny, thin discs with “self-levitating” properties that could help them remain in the stratosphere for over twenty years. “There’s a lot of talk about ‘particle X,’ or the optimal particle,” Driscoll said. “You want something that scatters light without absorbing it.” He added that some scientists have suggested using soot, a common volcanic by-product, because it could be self-levitating. The problem is that data from previous volcanic eruptions shows that soot absorbs low-wavelength light, which causes unexpected atmospheric effects. If past eruptions like Krakatoa are any indication—and they should be—massive soot injections would cool most of the planet, but changes in stratospheric winds would mean that the area over Eurasia’s valuable farmlands would get hotter. So the unintended consequences could actually make food security much worse.

It’s not clear how we’d accomplish the monumental task of injecting the particles, but Driscoll’s colleagues at Oxford believe we could release them from spigots attached to enormous weather balloons. Weather balloons typically fly in the stratosphere, and they could release reflective particles as a kind of cloud while remaining tethered to an ocean vessel. The stratosphere’s intense winds would carry the particles all around the globe. However, getting particles into the atmosphere isn’t the tough part.

The real issues, for Driscoll and his colleagues, are the unintended consequences of doping our atmosphere with substances normally unleashed during horrific catastrophes. Rutgers atmospheric scientist Alan Robock has run a number of computer simulations of the sulfate-particle injection process, and warns that it could destroy familiar weather patterns, erode the ozone layer, and hasten the process of ocean acidification, a major cause of extinctions.

“I think a lot about the doomsday things that might happen,” Driscoll said. Unintended warming and acidification are two possibilities, but geoengineering could also “shut down monsoons,” he speculated. There are limits to what we can predict, however. We’ve never done anything like this before.

If the planet starts heating up rapidly, and droughts are causing mass death, it’s very possible that we’ll become desperate enough to try solar management. The planet would rapidly cool a few degrees, and give crops a chance to thrive again. What will it be like to live through a geoengineering project like that? “People say we’ll have white skies—blue skies will be a thing of the past,” Cascio said. Plus, solar management is only “a tourniquet,” he warned. The greater injury would still need treating. We might cut the heat, but we’d still be coping with elevated levels of carbon in our atmosphere, interacting with sunlight to raise temperatures. When the reflective particles precipitated out of the stratosphere the planet would once again undergo rapid, intense heating. “You could make things significantly worse if you’re not pulling carbon down at the same time,” Cascio said. That’s why we need a way of removing carbon from the atmosphere while we’re blocking the sun.

Turning Earth into a Carbon-Eating Machine

One of the only geoengineering efforts ever tried was aimed at pulling carbon out of the atmosphere using one of the Earth’s most adaptable organisms: algae called diatoms. Researchers have suggested that we could scrub the atmosphere by re-creating the conditions that created our oxygen-rich atmosphere in the first place. In several experiments, geoengineers fertilized patches of the Southern Sea with powdered iron, creating a feast for local algae. This resulted in enormous algae blooms. The scientists’ hope was that the single-celled organisms could pull carbon out of the air as part of their natural life cycle, sequestering the unwanted molecules in their bodies and releasing oxygen in its place. As the algae died, they would fall to the ocean bottom, taking the carbon with them. During many of the experiments, however, the diatoms released carbon back into the atmosphere when they died instead of transporting it into the deep ocean. Still, a few experiments suggested that carbon-saturated algae can sink to the ocean floor under the right conditions. More recently, an entrepreneur conducted a rogue geoengineering project of this type off the coast of Canada. The diatoms bloomed, but the jury is still out on whether ocean fertilization is a viable option.

So it’s possible that algae will be helping us in our geoengineering projects. Another possibility is that we’ll be enlisting the aid of rocks. One of the most intriguing theories about how we’d manipulate the Earth into pulling down carbon was dreamed up by Tim Kruger, who heads the Oxford Martin School’s geoengineering efforts. I met with him across campus from Driscoll’s office, in an enormous stone building once called the Indian Institute and devoted to training British civil servants for jobs in India. It was erected at the height of British imperialism, long before anyone imagined that burning coal might change the planet as profoundly as colonialism did.

Kruger is a slight, blond man who leans forward earnestly when he talks. “I’ve looked at heating limestone to generate lime that you could add to seawater,” he explained in the same tone another person might use to describe a new recipe for cake. Of course, Kruger’s cake is very dangerous—though it might just save the world. “When you add lime to seawater, it absorbs almost twice as much carbon dioxide as before,” he continued. Once all that extra carbon was locked into the ocean, it would slowly cycle into the deep ocean, where it would remain safely sequestered. An additional benefit of Kruger’s plan is that adding lime to the ocean could also counteract the ocean acidification we’re seeing today. Given that geologists have ample evidence that previous mass extinctions were associated with ocean acidification, geoengineering an ocean with lower acid levels is obviously beneficial. “A caveat is that we don’t know what the environmental side effects of this would be,” Kruger said, echoing the refrain I’d already heard from Driscoll and others.

Kruger’s idea depends on something that the algae plan does as well. It’s called ocean subduction, and it refers to the slow movement of chemicals between the upper and lower layers of the ocean. Near the ocean surface, oxygen and atmospheric particles are constantly mixing with the water. When this layer becomes saturated with carbon, we see carbon levels rise in the atmosphere because the ocean can no longer act as a carbon sink. But the lower reaches of the ocean can sequester massive amounts of carbon beyond the reach of our atmosphere. “If the ocean were well mixed overall we wouldn’t have the problem with climate change,” he said. “But the interaction between the deep ocean and the surface is on a very slow cycle.” The goal for a lot of geoengineers is to figure out how to sink atmospheric carbon deep down into the water, where a lot of it will eventually become sediment. Kruger’s limestone plan wouldn’t deliver the carbon directly to the depths, the way the algae plan might have. Instead, the lime would keep more carbon locked into the upper layers of the ocean, allowing time for the ocean’s subduction cycle to carry more of it down into the deep.

Another possible method of pulling carbon down with rocks is called “enhanced weathering.” In chapter two, we saw how intense weathering from wind and rain on the planet during the Ordovician period actually wore the Appalachian Mountains down to a flat plain. Runoff from the shrinking mountains took tons of carbon out of the air, raising oxygen levels and sending the planet from greenhouse to deadly icehouse. The Cambridge physicist David MacKay recommends this form of geoengineering in his book Sustainable Energy—Without the Hot Air. “Here is an interesting idea: pulverize rocks that are capable of absorbing CO₂, and leave them in the open air,” he writes. “This idea can be pitched as the acceleration of a natural geological process.” Essentially, we’d be reenacting the erosion of the Ordovician Appalachians. MacKay imagines finding a mine full of magnesium silicate, a white, frangible mineral often used in talcum powder. We’d spread magnesium silicate dust across a large area of landscape or perhaps over the ocean. Then the magnesium silicate would quickly absorb carbon dioxide, converting it to carbonates that would sink deep into the ocean as sediment.

However we do it, enhanced weathering relies on the idea that we could take advantage of the planet’s natural geological processes to maintain the climate at a temperature that’s ideal for human survival. Instead of allowing the planet’s carbon cycle to control us, we would control it. We would adapt the planet to our needs by using methods learned from the Earth’s history of extraordinary climate changes and geological transformations. Of course, this all depends on whether we can actually make geoengineering work.

The Moral Hazard

There is what Kruger and his colleagues call a “moral hazard” in doing geoengineering research, because it could popularize the idea that geoengineering solutions are a magical fix for our climate troubles. If policy-makers believe that there’s a “cure” for climate change just around the corner, they may not try to cut emissions and invest in sustainable energy. “It’s as if a scientist had some good results while testing a cancer cure in mice, and we started telling kids, ‘Hey, it’s OK to smoke, we’re about to cure cancer,’” Kruger said. The point is that we’re very far from being certain that geoengineering would work, and until we’ve got a lot more hard data, we have to assume that the best way to slow down climate change is to stop using fossil fuels.

There’s another worry, too. “There’s a potential for nation-states to see geoengineering activities as a threat,” Cascio cautioned. Harking back to what Driscoll said about how stratospheric reflective particles might cause cooling in some places, but warming in others, Cascio warned that solar management might cause famines in some regions of the world while others cool down into fruitful growing seasons. So one country’s climate solution might be another one’s downfall. A failed experiment in stratospheric particle injection might not just be horrible weather—it might be nuclear retaliation from countries who feel attacked.

To deal with these moral and political hazards, Kruger and several colleagues created the Oxford Principles, a set of simple guidelines for geoengineers to follow in the years ahead. Spurred by a call from the U.K. House of Commons Science and Technology Committee, Kruger met with a team of anthropologists, ethicists, legal experts, and scientists to draft what he called “general principles in the conduct of geoengineering research.” The Oxford Principles call for:

Kruger emphasized that the principles must be simple for now, because geoengineering is still developing. First and foremost, he and his colleagues want to prevent any one country or company from controlling geoengineering technologies that should be used for the global public good. Principles 2 and 3 touch on the importance of openness in any geoengineering project. (The rogue geoengineer in Canada notably violated principle 2, getting absolutely no input from the public before seeding the waters.) Kruger feels strongly that as long as the public is informed and able to participate, they won’t fear geoengineering in the way many people have come to fear other scientific projects, like GMO crops. Finally, the principles aim to prevent unchecked experimentation that could lead to environmental catastrophe, while also avoiding regulations so restrictive that they stifle innovation. Principle 5, “governance before deployment,” speaks in part to Cascio’s concern about countries interpreting geoengineering as an attack. Before we turn the skies white, or fill the oceans with lime, we must form a governing body that allows nations and their publics to consent to change the fundamental geological processes of the world. “There are huge risks associated with doing this, but doing nothing has huge risks as well,” Kruger concluded.

To make Earth habitable for another million years, we will have to start taking responsibility for our climate in the same way we now take responsibility for hundreds of thousands of acres of farmland. Geoengineering of some kind is critical for our survival, because it’s inevitable that our climate will change over time. Certainly we’ll have to adapt to new climates, but we’ll also want to adapt the climate to serve us and the creatures who share the world’s ecosystems with us. If we want our species to be around for another million years, we have no choice. We must take control of the Earth. We must do it in the most responsible and cautious way possible, but we cannot shy away from the task if we are to survive.

Of course, we can’t stop at the edges of our atmosphere. If climate change doesn’t extinguish us, an incoming asteroid or comet could. That’s why we’re going to have to control the volume of space around our planet, too. We’ll find out how that would work in the next chapter.

WE ALREADY KNOW what an asteroid strike did to the creatures who lived during the Cretaceous period. Though it may not have been the sole driver of the K-T mass extinction, the 6.2-mile-diameter bolide that landed off the coast of Mexico roughly 65 million years ago devastated the planet, radically altering the Earth’s climate for possibly a decade or more. Among the scientists who study impacts, that one would have been classed as a 10 out of 10 on the Torino scale, a kind of Richter scale used to quantify impact hazards. Such disasters, where the entire planet is affected, are likely to strike once every 100,000 years or so (though not necessarily with the destructiveness of the K-T impact). That means we are long overdue for another one.

Will we wake up tomorrow to a newscaster telling us that humanity has six months to live, so we’d better make the best of things before an asteroid wipes us out?

Not likely. Contrary to Hollywood myths, we’d probably see an asteroid like the one that hit during the K-T mass extinction coming many years before it smashed into us. Less than two decades after scientists discovered the role an asteroid played in the planet’s most recent mass extinction, NASA launched an asteroid-spotting program called Spaceguard. The goal of Spaceguard was to discover and track 90 percent of near-Earth objects larger than a kilometer. A near-Earth object, or NEO, refers to asteroids, meteoroids, comets, and other heavenly bodies whose orbits around the sun bring them close to our own orbit. Most NEOs are not dangerous—they’re either so small that our atmosphere would burn them up, or they zip past us millions of kilometers away. That being said, there is a class of NEO called potentially hazardous objects, or PHOs, and these are the ones we have to be worried about. To achieve PHO status, an object has to be larger than 1 km and its likely trajectory must take it closer than 7,402,982.4 km from Earth.

That sounds pretty far away, especially when you consider that we’ve had some near misses over the past two decades when sizable asteroids have come within thousands of kilometers of the planet (some would have caused explosions comparable to a nuclear bomb if they had hit). But our solar system is a constantly shifting set of gravitational fields, and the orbits of small objects shift a lot over time. If an asteroid zooms past Jupiter or another planet on its way to us, gravity from that other body could easily pull the asteroid into a new course, converting it from distant to deadly. That’s why astronomers want to keep a sharp eye on any large rocks or balls of ice that come within a few million kilometers of our orbit.

The good news is that over the past two decades, we’ve gotten pretty good at spotting and tracking NEOs and PHOs. The bad news is that, at least right now, nobody is quite sure what we’d do in what NASA astronomer and asteroid hunter Amy Mainzer calls one of the most hopeful scenarios. That would be when an astronomer—possibly Mainzer herself—verifies tomorrow that there’s a mile-diameter asteroid twenty years out, on a direct collision course with Earth.

Preparing for an Asteroid Hit

Mainzer is obsessed with seeing into space. That’s why she’s worked on instrumentation for NASA spacecraft like the WISE (Wide-field Infrared Survey Explorer) satellite, whose sole job was to map as much of the sky as possible using an infrared telescope. Once the WISE mission was complete, Mainzer and her colleagues were able to reprogram the craft in 2010 to scan the sky for NEOs—they dubbed this mission NEOWISE. It was the NEOWISE mission that helped complete the Spaceguard project by identifying enough one-kilometer-or-bigger NEOs that we can say with confidence that we now know where 90 percent of them are. In all, we’ve located nearly 900 NEOs of that size. “That’s good for Earthlings,” Mainzer told me lightly by phone from her office at the Jet Propulsion Lab in California. But then, more seriously, she added, “We don’t know where most of the other ones are.” In her most recent work, Mainzer gathered data on PHOs among asteroids, and she and her colleagues estimate there might be as many as 4,700 of these potential impactors that are bigger than 100 meters. To give you a sense of what that means, a 100-meter asteroid wouldn’t cause a mass extinction, but it would easily flatten a city or a small country. If it landed in the ocean, the tsunamis it generated could do profound damage to coastal areas.

Given that our local volume of space is swarming with deadly rocks, why aren’t we bombarded all the time? The simple answer is that we are. Every day, we are hit by tiny NEOs, most of which we never notice because they flame out before reaching the Earth’s surface. “You know the video game Asteroids?” Mainzer asks. Of course I do. “Well, it’s actually pretty accurate. Asteroids break up and make more little pieces. And there are far more little pieces than big pieces.” Aside from the relative rarity of larger asteroids, there’s also the fact that our solar system is a dynamic, constantly shifting sea of debris. All the overlapping gravitational fields of the planets and their moons may send rocks spinning into our path, but they also send them spinning out of it, too. “If you put a particle in near-Earth space, it doesn’t stay stable,” Mainzer explained. “After about ten million years, it will go into the outer solar system, crash into the sun, or crash into the Earth.” Keep in mind that 10 million years is nothing to a planet like Earth, which has been around for 4.5 billion years. Essentially, there’s only a short time window for these NEOs to do any damage before they’re hurled elsewhere by gravity.

Still, Mainzer notes, there are probably “source regions” of the asteroid belt that are constantly resupplying the inner system with new NEOs. Possibly these source regions are shooting out new NEOs because of gravitational resonances with Mars and Jupiter, the two planets whose orbits sandwich the asteroid belt. “I like to think of it as a flipper on a pinball machine,” Mainzer said. “That’s what these resonances are like in the main belt—if an asteroid drops into one, it can get hurled very far from its original location.”

With the amount of data we’ve gathered from satellites like NEOWISE, it’s reasonable to hope we’d have twenty years to deal with an asteroid or other PHO big enough to cause destruction over the entire Earth. Knowing where most of the large NEOs are can help astronomers to track their movements and determine whether they’re on a collision course. That said, collision courses are always expressed in probabilities. We can’t predict precisely where gravity will tug one of these objects on its way to our cosmic neighborhood. Also, we’re still struggling to track objects that could cause tremendous damage without actually destroying humanity. “Your warning time depends on the design of your instruments,” Mainzer said. She’s currently working on plans for a new space telescope, dubbed NEOCam, designed to spot objects smaller than 100 meters and to find more of those PHOs. “We’re designing it to give us decades of warning,” she said. The goal for Mainzer and others in her field is to get 20 to 30 years of warning for a likely impact, so that we have as many options as possible for stopping it.

Defending the Planet

Most people who are serious about defending Earth from PHOs don’t talk about blowing things up. As Mainzer explained with the 8-bit game Asteroids, the problem is that asteroids tend to break down into smaller asteroids. Nuking an incoming object might not do much more than shower our planet with dozens of burning chunks rather than one big one. The damage would be roughly the same. The reason Mainzer’s data-gathering is so crucial is that the further away an asteroid is when we spot it, the easier it will be to nudge it out of the way. That’s right—our best bet is to nudge it. “Blowing up asteroids may be fun, but an Aikido move would be better,” Mainzer said, only half joking. “Having time gives you the ability to move its trajectory without a lot of energy.”

The question of how to finesse this Aikido move in space has been the longtime concern of a loose coalition of scientists, policy-makers, and government representatives associated with the Center for Orbital and Reentry Debris Studies. Run by aerospace engineer William Ailor, the Center has developed a series of suggestions over the past 15 years for how we’d deal with asteroid threats. An affable man with tidy gray hair and a touch of the South in his speech, Ailor sketched out how he thought an impact scenario might unfold. “Anyone can find these things,” he said. “There are amateur astronomers all over, as well as more formal programs in space agencies. Most likely, it would be spotted by that community.” If it’s a smaller object, we might have very little time to prepare. “People like to think we’ll have twenty years, but we might only have a few years.”

The next big hurdle wouldn’t be the question of how to divert the asteroid, though. Say, for example, Mainzer’s NEOCam is in orbit and her team spots an object bigger than 1 km that has a 1-in-50 probability of smashing into the Earth. “Should we spend money on that now?” Ailor asked. “Given the fact that it takes you years to build a new payload and fly a mission out to do something, you may have to start spending money before you’re certain it’s going to hit. And that’s the challenge for decision-makers.” The problem is that every PHO is a probability… until it isn’t. And the time to act decisively to push an incoming object out of the way is almost inevitably going to be long before we can establish that a collision is a certainty. Meanwhile, as the object hurtles closer to us in space, the less likely it is that we’ll be able to gently nudge it into a new orbit, out of our way.

So who would have to step up and push the world to launch anti-PHO spacecraft? The U.N. Committee on the Peaceful Uses of Outer Space has a group called Action Team-14 that deals with NEOs, and would likely be the first agency to coordinate Earth’s defense in this situation. Provided they can get buy-in from countries and corporations with the means to build spacecraft for the mission—and that’s a big if—the group would have to decide exactly what method of PHO deterrence would work best. Ailor’s company, the Aerospace Corporation, did a study in 2004 on what would be required to take a 200-meter object from a 1-in-100 probability of hitting Earth to 1 in 1,000,000. “You have to launch quite a few spacecraft,” Ailor said. “There’s a misconception that you would send up just one vehicle.” Redundancy would be crucial, in case one of the crafts fails—and besides, some techniques for moving the object require multiple spacecraft to work. Also, despite what we saw in the asteroid-nuking flick Armageddon, the vehicle would be a remote-controlled robotic craft. “If a human can get there, it’s way too close,” Ailor asserted.

If we have enough time, we’d want to try what Ailor called slow-push techniques. One would involve using a swarm of small spacecraft equipped with lasers designed to boil material off the surface of the object. As the PHO spat pieces of itself into space, enough thrust would be generated to gently move it out of its deadly path toward Earth. Another possibility would be to create a “gravity tractor” with one or more spacecraft. Parking bulky objects like other asteroids or big spacecraft near the distant object might generate enough gravitational pull to move it just enough. Many years later, this small perturbation would elegantly divert its course into a completely harmless orbit. Both of these techniques are untested. But as more spacecraft venture to NEOs and the asteroid belt over the next decade, we’re likely to see experiments to test whether these techniques could, in fact, jar a large object out of its current orbit.

What if the asteroid were heading toward us today, and we hadn’t had a chance to test the slow-push systems? “We don’t have anything off the shelf other than a kinetic impactor,” Ailor said casually, as if he were talking about computer parts. A kinetic impactor is “basically hitting it with a rock,” he explained. We’ve already tried this method on a comet with NASA’s Deep Impact mission, when a probe hit the Tempel 1 comet with a giant copper slug, dislodging huge amounts of dust and ice. Tempel 1’s orbit was perturbed slightly. So we know for certain that if we hit an incoming object with slugs or rocks, we have a good chance of redirecting it. “If you have one that gets too close or is bigger, you might have to use a nuke to move it,” Ailor conceded. That’s a last resort, and also untested.

The problem is that even our “off the shelf” kinetic-impactor solution would be tough. “You’d have to pull a craft together, grab the right kind of payload to do what you wanted, and find a launch pad,” Ailor said, seeming to be mentally ticking off a list he’d pondered many times. On top of that, there would be the issue of how to inform the public without causing either mass panic or denial. It’s easy to imagine people voting against an expensive anti-PHO program if there were only a 1-in-500 chance of mass extinction. Still, it’s possible we might band together as a civilization to deal with this existential threat, and fail anyway. As Ailor put it, “Of course, you might miss.”

In the Event of Fallen Civilization, Please Open This File

If we’re facing an impact that’s a 10 on the Torino scale—that is, from an asteroid comparable to the one that hit at the K-T—we are certainly facing a mass extinction. The world would be wrapped in fires, and cities would be shaken by quakes, broiled by volcanic eruptions, and flooded by tsunami waters. Over the long term, the climate would be transformed by aerosols thrown into the stratosphere. How would we survive?

Initially, our survival would depend on retreating to the kinds of underground cities we discussed in chapter 17. The immediate aftereffects of the hit would be similar to a massive nuclear war, minus the radioactive fallout. Underground, we would be relatively safe from the worst of the firestorms and other disasters. Aboveground, temperatures and fires would die down relatively quickly. Within weeks, we’d be able to poke our heads back up and see the roiling clouds of dust that had replaced our sky. And that’s when our real troubles would begin. We’d likely suffer through something like a nuclear winter. Alan Robock, the atmospheric scientist who warned against solar-management geoengineering with particles in the stratosphere, was among the first scientists to suggest that supermassive explosions would result in planetary cooling. And the cold would likely intensify for several years. In an early paper about nuclear winter, Robock outlines a scenario that sounds like a mild icehouse. The first year after the explosion—in this case, an asteroid strike—we’d see a global buildup of ice and snow and lowering of temperatures by about two degrees. But as the cold deepened, the planet’s snowy surface would reflect even more light—creating a runaway effect that would cool us down possibly as much as 15 or 16 degrees in the following several years.

Without sunlight, agriculture would grind to a halt and wild plants would die back. Herbivores would die, and then the carnivores who fed on them would die out, too. Creatures who dwelled near the surface of the water would suffer in the immediate effects of the hit. Then, over time, runoff from the decimated land would fill the oceans with carbon and create deadly pockets of anoxic waters. Humans would have to rely on greenhouses for food, as well as whatever we could cultivate with little sunlight. Mushrooms, fungus, and insects would play a much bigger role in our diets than they do today.

There is also the distinct possibility that enough people would be killed in the strike that it would be impossible to maintain our civilization at its current level of development and energy needs. Megacities and high-tech societies require many people with specialized knowledge to make them function, and if only a few million people are left alive on the planet, it’s unlikely that we’ll have the right combination of skills to resurrect New York or Tokyo. What would we do if we had to rebuild human civilization from scratch? This is the kind of question that dogs apocalyptic science fiction, but preoccupies people in the real world, too. Alex Weir, a software developer based in Zimbabwe, is part of a small group that maintains the CD3WD database, a relatively small set of computer files that contain as much human knowledge as possible about what amounts to a pre-technological civilization. There are sections devoted to basic medicine, agriculture, town building, and power generation. At 13 gigabytes, it’s easily stored on a few DVDs, or (ideally) printed out as a thick sheaf of papers and stored in a three-ring binder. The idea is to keep the CD3WD database in your survival kit, a backup copy of everything history has taught us about creating an early industrial society. It is one of the simplest and most profound examples of how survival requires us to remember what has come before. If people need guidance with rebuilding the world after the icehouse is over, CD3WD and similar projects can help us restart civilization as quickly as possible.

It is inevitable that the Earth will be on a collision course with a PHO at some point. Obviously, our first duty is to keep mapping the skies, tracking NEOs, and perfecting our asteroid-nudging technologies. But we also need to accept that the Earth isn’t the safest place for us if we want to survive for another million years. We need to scatter to other planets and moons, building structures in space so that even if Earth is wiped out, humanity will survive. That’s why one of the keys to long-term existence involves creating devices that will help us escape the planet. One such device is the subject of the next chapter.

EVENTUALLY WE’LL HAVE to move beyond patrolling our planetary backyard and start laying the foundations for a true interplanetary civilization. Asteroid defense and geoengineering will only take us so far. We need to scatter to outposts and cities on new worlds so that we’re not entirely dependent on Earth for our survival—especially when life here is so precarious. Just one impact of 10 on the Torino scale could destroy every human habitat here on our home planet. As horrific as that sounds, we can survive it as a species if we have thriving cities on Mars, in space habitats, and elsewhere when the Big One hits. Just as Jewish communities managed to ensure their legacy by fleeing to new homes when they were in danger, so, too, can all of humanity.

The problem is that we can’t just put our belongings into a cart and hightail it out of Rome, like my ancestors did when things got ugly in the first century CE. Currently, we don’t have a way for people to escape the gravity well of planet Earth on a regular basis. The only way to get to space right now is in a rocket, which takes an enormous amount of energy and money—especially if you want to send anything bigger than a mobile phone into orbit. Rockets are useless for the kind of off-world commuter solution we’ll need if we’re going to become an interplanetary civilization, let alone an interstellar one. That’s why an international team of scientists and investors is working on building a 100-kilometer-high space elevator that would use very little energy to pull travelers out of the gravity well and up to a spaceship dock. It sounds completely preposterous. How would such an elevator work?

That was the subject of a three-day conference I attended at Microsoft’s Redmond campus in the late summer of 2011, where scientists and enthusiasts gathered in a tree-shaded cluster of buildings to talk about plans to undertake one of humanity’s greatest engineering projects. Some say the project could get started within a decade, and NASA has offered prizes of up to $2 million to people who can come up with materials to make it happen.

The physicist and inventor Bryan Laubscher kicked off the conference by giving us a broad overview of the project, and where we are with current science. The working design that the group hopes to realize comes from a concept invented by a scientist named Bradley Edwards, who wrote a book about the feasibility of space elevators in the 1990s called The Space Elevator. His design calls for three basic components: A robotic “climber” or elevator car; a ground-based laser-beam power source for the climber; and an elevator cable, the “ribbon,” made of ultra-light, ultra-strong carbon nanotubes. Edwards’s design was inspired, in part, by Arthur C. Clarke’s description of a space elevator in his novel The Fountains of Paradise. When you’re trying to take engineering in a radical new direction that’s never been tried before, sometimes science fiction is your only guide.

What Is a Space Elevator?

A space elevator is a fairly simple concept, first conceived in the late nineteenth century by the Russian scientist Konstantin Tsiolkovsky. At that time, Tsiolkovsky imagined the elevator would look much like the Eiffel Tower, but stretching over 35,000 kilometers into space. At its top would be a “celestial castle” serving as a counterweight.

A century after Tsiolkovsky’s work, Bradley speculated that a space elevator would be made of an ultra-strong metal ribbon that stretched from a mobile base in the ocean at the equator to an “anchor” in geostationary orbit thousands of kilometers above the Earth. Robotic climbers would rush up the ribbons, pulling cars full of their cargo, human or otherwise. Like Tsiolkovsky’s celestial castle, the elevator’s anchor would be a counterweight and space station where people would stay as they waited for the next ship out. To show me what this contraption would look like from space, an enthusiast at the Space Elevator Conference attached a large Styrofoam ball to a smaller one with a string. Then he stuck the larger ball on a pencil. When I rolled the pencil between my hands, the “Earth” spun and the “counterweight” rotated around it, pulling the string taut between both balls. Essentially, the rotation of the Earth would keep the counterweight spinning outward, straining against the elevator’s tether, maintaining the whole structure’s shape.

Once this incredible structure was in place, the elevator would pull cargo out of our gravity well, rather than pushing it using combustion. This setup would save energy and be more sustainable than using rocket fuel. Getting rid of our dependence on rocket fuel will reduce carbon emissions from rocket flights, which today bring everything from satellites to astronauts into orbit. We’ll also see a reduction in water pollution from perchlorates, a substance used in making solid rocket fuel, and which the Environmental Protection Agency in the United States has identified as a dangerous toxin in our water supplies.

A space elevator would be a permanent road into space, making it possible for people to make one or more trips per day into orbit. Passengers could bring materials up with them so that we could start building ships and habitats in space. Once we started mining and manufacturing in space, elevators would be used to bring payloads back down, too. Most important, a working space elevator is many thousands of times cheaper than the one-time-use Soyuz rockets that bring supplies to the International Space Station, only to destroy themselves in Earth’s atmosphere. NASA reports that each Space Shuttle launch cost about $450 million. Much of that money was spent on storing enough fuel to complete the round-trip back to Earth. But groups working on space-elevator plans believe their system could reduce the cost of transporting a pound of cargo into space from today’s $10,000 price tag to as little as $100 per pound.

Getting Ready to Build

The elevator would be attached to the Earth at the equator, where geostationary orbit happens, probably on a floating platform off the coast of Ecuador in international waters. This is a likely building site because it is currently an area of ocean that experiences very little rough weather, and therefore the elevator could climb out of our atmosphere with as little turbulence as possible. According to Edwards’s plan, the elevator ribbon would stretch 100,000 kilometers out into space (about a quarter of the distance to the Moon), held taut by a counterweight that could be anything from a captured asteroid to a space station. A ride up would take several days, and along the ribbon would be way stations where people could get off and transfer to orbiting space stations or to vessels that would carry them to the Moon and beyond.

The elevator car itself is the easiest thing for us to build today. It would be an enormous container, with atmospheric controls for human cargo, connected to large robotic arms that would pull the car up the ribbon hand over hand. We already have robotic arms that can scale ropes and lift incredibly heavy objects. This aspect of the space elevator is so widely understood that the Space Elevator Conference sponsored a “kids’ day” that included LEGO space-elevator-climber races. Robots designed by teens and kids competed to see which could climb “ribbons” attached to the ceiling and place a “satellite” at the top.

Of course it will take some effort to get from LEGO climbers to lifters big enough to haul components of a space hotel up through thousands of kilometers of atmosphere and space. But this is within the capabilities of our current industrial technology. So we’ve got our elevator car. But how will it be powered?

One of the many arguments in favor of the elevator concept is that it will be environmentally sustainable. The dominant theory among would-be space-elevator engineers at this point is that we’ll install lasers on the space-elevator platform, aimed at a dish on the elevator that will capture the beam and convert it to power. This technology is also within our reach. In 2009, NASA awarded $900,000 to LaserMotive for its successful demonstration of this so-called “wireless power transmission” for space elevators. In 2012, NASA offered a similar prize for a power-beaming lunar rover. The biggest problem with the power-beaming idea currently is that we are still looking at fairly low-power lasers, and as the space elevator ascended higher into the atmosphere the beam from such a laser would scatter and be blocked by clouds. It’s possible that only 30 percent of the beam would reach the dish once the elevator was in space.

Still, we have seen successful demonstrations of power beaming, and companies are working on refining the technology. We don’t quite have our perfect power beam yet, but it’s on the way.

The Missing Piece: An Elevator Cable

At the Space Elevator Conference, participants devoted an entire day to technical discussions about how we’d build the most important part of the space elevator: its cable, often called the ribbon. Again, most theories about the ribbon come from Edwards’s plans for NASA in the 1990s. At that time, scientists were just beginning to experiment with new materials manufactured at the nanoscale, and one of the most promising of these materials was the carbon nanotube. Carbon nanotubes are tiny tubes made of carbon atoms that “grow” spontaneously under the right conditions in specialized chambers full of gas and chemical primers. These tubes, which look a lot like fluffy black cotton, can be woven together into ropes and textiles. One reason scientists believe this experimental material might make a good elevator cable is that carbon nanotubes are theoretically very strong, and can also sustain quite a bit of damage before ripping apart. Unfortunately, we haven’t yet reached the point where we can convert these nanoscopic tubes into a strong material.

Carbon nanotube material is so light and strong that the elevator cable itself would be thinner than paper. It would literally be a ribbon, possibly several meters across, that the robotic cars would grip all the way up into space. Every year at the Space Elevator Conference, people bring carbon nanotube fibers and compete to see which can withstand the greatest strain before breaking. Winners stand to gain over a million dollars from NASA in its Strong Tether Challenge. Sadly, the year I attended, nobody had fibers that were strong enough to place (but there’s always next year!).

Researchers from the University of Cincinnati and Rice University, where there are nanomaterials labs investigating the tensile strength of carbon nanotubes, explained that we are years away from having a working elevator ribbon made of carbon nanotubes. Though the microscopic tubes on their own are the strongest material we’ve ever discovered, we need to make them into a “macromaterial”—something that’s big enough to actually build with. And making that transition into a macromaterial can be difficult, as the University of Cincinnati chemical engineer Mark Haase explained:

Haase added that the barrier here is that we need to invent an entirely new material, and then figure out how to string it between the Earth and a counterweight without it breaking. That’s not a trivial problem, even once we reach the point where we can create a carbon nanotube ribbon. What if a huge storm hits while the elevator is climbing into the stratosphere? Or what if one of the millions of pieces of junk orbiting the Earth, from bits of wrecked satellites to cast-off chunks of rockets, slams into the elevator ribbon and rips it? This may be an enormous structure, but it will have some vulnerabilities and we need to determine how we’ll protect it.

How do you dodge an incoming piece of space junk that’s headed right to your elevator ribbon? Engineer Keith Lofstrom suggested mounting the ribbon on a massive maglev platform designed to move the line in any direction very rapidly, basically yanking it out of the way. Rice University materials-science researcher Vasilii Artyukhov argued that we might not want to use carbon nanotubes at all, because they break in several predictable ways, especially when they’re under constant strain and bombarded with cosmic rays from the sun. He thought an alternative material might be boron nitride nanotubes, though these are even more experimental than carbon nanotubes at this point.

Ultimately, the elevator cable is our stumbling block in terms of engineering. But there are also social and political issues we’ll have to confront as we begin our journey into space.

Kick-starting the Space Economy

Building the elevator goes beyond engineering challenges. First, there’s the legal status of this structure. Who would it belong to? Would it be a kind of Panama Canal to space, where everybody pays a toll to the country who builds it first? Or would it be supervised by the U.N. space committees? Perhaps more urgently, there is the question of how any corporation or government could justify spending the money to build the elevator in the first place.

One of the world experts on funding space missions is Randii Wessen, an engineer and deputy manager of the Project Formulation Office at the Jet Propulsion Laboratory. An energetic man with a quick wit, Wessen has a lifetime of experience working on NASA planetary exploration missions, and now one of his great passions is speculating about economic models that would support space flight. We’ve recently witnessed the success of Elon Musk’s private company SpaceX, whose Falcon rocket now docks with the International Space Station, essentially taking on the role once played by the U.S. government–funded Space Shuttles. “The bottom line is that you need to find a business rationale for doing it,” Wessen told me. “What I would do is parallel the model that was used for the airplane.” He swiftly fills in a possible future for commercial spaceflight, by recalling how airplanes got their start:

Like many other people in the slowly maturing field of commercial spaceflight, Wessen is convinced that government contracts and tourism represent the first phase of an era when sending people to space is economically feasible. He noted that SpaceX’s founder, Musk, has said it’s reasonable to expect payload costs to go down to roughly $1,000 per kilogram. “Everything cracks open at that point,” Wessen declared. SpaceX isn’t the only private company fueling Wessen’s optimism. Robert Bigelow, who owns the Budget Suites hotel chain, has founded Bigelow Aerospace to design and deploy space hotels. In the mid-2000s, Bigelow successfully launched two test craft into orbit, and he is now working on more permanent orbiting habitats. Meanwhile, Moon Express, a company in Silicon Valley, is working closely with NASA and the U.S. government to create crafts that could go to the Moon. Its founders hope to have a working prototype before 2015.

Google is another Silicon Valley mainstay that is investing in the burgeoning space economy. The company recently announced its Google Lunar X Prize, which will award up to $30 million to a privately funded company that successfully lands a robot on the Moon. To win the prize, the robot must go at least 500 meters on the Moon’s soil, called regolith, while sending video and data back to Earth. Alex Hall, the senior director of the Google Lunar X Prize, described herself as “the Lunar Chamber of Commerce.” At SETICon, a Silicon Valley conference devoted to space travel, Hall told those of us in the audience that the Lunar X Prize is “trying to kick-start the Lunar Space Economy.” She said the group measures its success not just in robots that land on the Moon, but in creating incentives for entrepreneurs to set up space-travel companies in countries where no orbital launch facilities have existed before. Mining and energy companies are among the groups most interested in what comes out of the Google X Prize, she said. The X Prize “is the first step to buying a ticket to the Moon, and using the resources on the Moon as well as living there.” Bob Richards, a cofounder of Moon Express, is one of the contenders for the Google X Prize. He spoke on the same panel as Hall at SETICon, and amplified her arguments. “This isn’t about winning—it’s about creating a new industry,” he explained. “We believe in a long-term vision of opening up the Moon’s resources for the benefit of humanity, and we’re going to do it based on commercial principles.”

The space elevator is the next stage in the space economy. Once we have a relatively cheap way of getting into orbit, and a thriving commercial space industry partly located on the Moon, there will be a financial incentive to build a space elevator—or more than one. It may begin with funding from governments, or with a space-obsessed entrepreneur who decides to invest an enormous amount of money in a “long-term vision” of the kind Richards described. Already, we see the first stirrings of how such an arrangement might work, with a future Google or Budget Suites providing the initial capital required to move the counterweight into place, drop the ribbon from space down to the ocean, and get the beam-powered robotic climber going.

Once we’ve got a reliable and sustainable method of leaving the planet, we can begin our exodus from Earth in earnest. The space elevator, or another technology like it, could be the modern human equivalent of the well-trodden path that took humans out of Africa and into what became the Middle East, Asia, and Europe. It’s the first leg on our next long journey as we scatter throughout the solar system.

MOST OF US can imagine humans living in a future full of space elevators, and even cities on the Moon. But we usually picture our distant progeny in that future looking exactly the way we do now, the way people do in Star Trek. And yet of all the possible futuristic scenarios we’ve explored in this book, our continued evolution as a species is one of the most certain. We are going to evolve into creatures different from humans today—perhaps as different as we are from Australopithecus. The question is just how fast this will happen, and whether we’ll use what we know about genetics to steer the process.

This concern is especially important in the context of how humans will become a space-faring civilization. We are adapted nicely to live inside the thin layer of gas surrounding the rock we call home, but in many ways that makes us terrible space travelers. First of all, the Earth’s magnetic field protects us from the enormous amount of radiation in space, so our bodies never evolved a good defense against radiation damage. Solar radiation and high-energy particles would bombard our bodies on a regular basis in space and on places like the Moon and Mars, which have much weaker magnetic fields than we do at home. A person living off-world would have a high probability of developing cancer, infertility, or other radiation-induced problems. Another issue for people in space will be our extremely specific needs when it comes to sustenance. Because we draw our energy from foods native to Earth, it will never be a matter of humans colonizing space alone. We will have to bring a whole biosphere along with us, including plants and animals, as well as the exact mix of oxygen, nitrogen, and other gases we require to breathe. There are a host of other issues, too, such as the human body’s tendency to atrophy in low gravity, and the fact that our life spans are so short that it would take several generations to reach even the closest neighboring stars.

For all these reasons and more, it’s likely that the project of exploring space will involve a parallel project to adapt our bodies to life in environments radically different from the one where we evolved. It’s possible that we’ll become cyborgs, beings who are half biological and half machine. We may tweak our genomes to be radiation-resistant. Or we may, according to some futurists, become so technologically advanced that we’ll be able to convert the galaxy into a giant version of Earth. No matter what happens, the humans who live in space will be different from the humans on Earth today.

Changing Ourselves to Live in Space

How would we go about modifying ourselves to be more space-worthy? If anyone would know, it would be a synthetic biologist. In chapter 18, we explored how synthetic biology could revolutionize cities by providing us with buildings that could heal themselves or even grow. The field has obvious applications for any project to create humans suited for life beyond Earth as well. Leaving aside for a moment the ethical issues of engineering space-ready humans, synthetic biology could eventually reach a point where we could accurately predict how modified human genomes would function—and then implant them in the next generation. Though such knowledge may be centuries away, it’s very possible we might one day be guiding ourselves through a phase of evolution aimed at, for example, giving birth to children who could live on Mars unharmed.

To find out how this might work, I visited the UC Berkeley synthetic biologist Chris Anderson, a pioneer in the field whose research focuses in part on defining the most efficient and ethical methods for pursuing synthetic biology. A slender man with a sly smile, Anderson launched into an explanation of the future direction for synbio (as it is fondly known) by first seizing a piece of putty on his desk and vigorously smashing it between his hands. “I love this stuff!” he enthused. Apparently there is a reason the substance is sometimes marketed as “thinking putty,” because Anderson’s train of thought matched the pace at which he mashed out different shapes, which each looked like a new phylum of bacteria. Synbio researchers, he said, look at every organism in terms of its component parts. They don’t want to engineer new life-forms—not exactly. Instead, they want to engineer parts, especially at the genetic level. “Fundamentally, what we’re talking about is moving genes between organisms,” Anderson said. “We want to write whole genomes eventually. But it’s all based on components, and having the ability to predict how they will add together.”

A synbiologist looks at life-forms the same way a mechanic looks at an engine. To the mechanic, the engine is a set of interoperable parts, and some of those parts could just as easily be used in another machine. Likewise, a biological part like a gene or a protein could easily be repurposed for use in another organism. In fact, Anderson pointed out, a synbio project would typically look at a particular part—a gene, for example—in its many variants across a thousand organisms. Let’s say a synthetic biologist is studying a gene that thousands of plants use in photosynthesis. Her goal in that research would be to predict how the gene would function if it were used as a part in another organism. She would base her predictions on how the gene behaved in the thousand species where it currently exists. “This is a paradigm shift,” Anderson said. “We’ve stopped focusing on studying naturally existing things and are instead building things one gene at a time. Basically, it’s biological systems as a sum of their parts.”

Anderson’s work focuses on bacteria, and when I started to ask about modifying humans he wrinkled his nose. “I don’t touch mammalian cells,” he quipped. “They’re such a mess.” And this messiness is nothing compared with the moral quandaries presented by a future where we might use synbio to make Martians. The main problem, he said, is that we can’t experiment on humans the way we do with bacteria. To make accurate predictions about what a gene will do in a given organism, you have to run thousands of tests—some of which reveal that the gene does the opposite of what you’d hoped. “If you are playing with enhancing human intelligence, for example, you might create somebody who is brain dead rather than smart,” Anderson mused. “There would be so many accidents because this work involves a lot of fundamental uncertainty.”

Given all the risks and their consequences, he added, “It’s hard for me to see how you could even develop enough design theory to be able to safely build a human. It’s not going to be socially acceptable to tweak a human in a way that could cause them to be born grossly broken. No one’s going to go for that.” But, he conceded, it might be possible in a future where we had “a radical transformation in our ability to predict things” on the genetic level. If we had absolute certainty about how a given gene would work in a human, then the risks would be minimal. However, Anderson was extremely dubious we’d ever reach this point. He emphasized several times that he couldn’t believe that humans would ever be willing to modify our germ lines to change our species at a genetic level.

His sentiments were echoed by Claudia Wiese, a Lawrence Berkeley Lab geneticist who studies how humans respond at a cellular level to radiation in space. “During a long-duration manned space flight, substantial numbers of cells in a human body, [approximately] 30%, will be traversed by at least one highly ionizing particle track,” she told me via e-mail. “Highly ionizing particles” are the most dangerous kind of radiation we can encounter in space—these energetic particles shoot through the body like infinitesimally small bullets, cutting through everything in their path, including tissues and DNA. The danger is that they would damage a cell’s DNA but not kill the cell outright. Subsequently, the cell would replicate with mutated DNA, a situation that can lead to cancer.

Wiese and her colleagues believe some variants of DNA-repair genes may be better at dealing with radiation damage than others, but they’re nowhere near being able to tweak these genes to make humans radiation-proof. “I think that we are a long way away from gene therapy,” Wiese said. “At this point, the use of appropriate countermeasures”—like drugs such as antioxidants—“may be a more immediate and feasible way to mitigate the detrimental effects of space radiation.” Still, her research and that of other geneticists working with NASA suggest that we may one day know which genes control DNA repair. Once we are able to predict the behaviors of these genes, future space-farers might tweak their genes to respond quickly and effectively when bombarded with highly ionizing particles beyond Earth’s protective magnetic envelope.

But some synbio researchers aren’t sure this is a good idea. Daisy Ginsberg, a London designer who works with synthetic biologists on the ethical implications of their work, said that we could take the modification of humanity way too far. Sipping tea in a London restaurant, Ginsberg’s sunny disposition belied a deep pessimism. “I’m of the mind that we’re going to fuck everything up,” she said cheerfully. “We’re going to poison the Earth and it’s going to be unpleasant and expensive. I think we’re going to become Morlocks.” Ginsberg was referring to H. G. Wells’s novel The Time Machine, in which the author predicts that humans will evolve into two species: the Morlocks, a hyper-technological, warlike group who live underground, and the Eloi, a dim-witted but peaceful group who are prey to the Morlocks. Ginsberg was basically predicting that humans would evolve to be hideous monsters who destroy the Earth and prey upon each other. But what about modifying ourselves to live beyond Earth, so that we stop destroying our home world? Ginsberg was dubious about that, too. “I think it’s unethical to colonize space because we’ll make a mess there as well,” she said. “I’m sure we’ll be modifying everything.”

One of Ginsberg’s most memorable design projects is called “pollution sensing lung tumor.” It’s a sculpture of a pair of human lungs, made entirely out of sparkling red crystals. It comes from one of Ginsberg’s scenarios for a synbio future in which the environment is full of materials made out of biological components. One material might be a pollution sensor made from thin crystalline sheets of carbon monoxide–sensing bacteria. What if some of those biological components got loose, and started spreading in the air or water supplies? These bacterial sensors might enter the lungs of a smoker, proliferating there because of all the “pollution” they discover. Suddenly, instead of a bacterial infection that gives you a cough, you’ve got an infection that builds crystal sensors in your respiratory tract. The crystalline structure Ginsberg created, which at first appears to be a pair of lungs, actually represents a tumor that has been removed from a woman’s body.

Ginsberg got the idea for this project after seeing plans for such sensors, as well as for materials like the self-healing concrete I described in chapter 18. Ultimately, her concern mirrored Anderson’s. We might create synbio organisms with the best of intentions, but end up modifying humans in ways that make them sick or “grossly broken,” as Anderson put it. At the same time, Ginsberg strongly advocated against “viewing nature as a fixed thing.” Looking out the window at the busy street, she pondered out loud: “Maybe it’s ethical to disrupt nature after all. It’s just that there are so many questions that we don’t know answers to. I don’t know whether we can ever actually think it over enough to do it well.”

Though neither Anderson nor Ginsberg could imagine humans modifying themselves successfully, science-fiction writers have no trouble imagining this at all. We already explored Octavia Butler’s vision of a transformed humanity in her novels, and she’s not the only one. The British author Paul McAuley has suggested in recent novels like The Quiet War that humans will modify themselves as they colonize the solar system. He imagines a war between the Inners, people like Ginsberg from the inner solar system who think it’s morally reprehensible to modify their germ lines, and the Outers, people who have genetically modified themselves to adapt to life on the moons of Jupiter and beyond. McAuley began his career as a botanist at Oxford, and his background as a scientist informs his work. He told me how he thinks future humans might justify doing the human genetic experiments Anderson said “nobody would go for.” It all comes down to necessity. The Outers, he told me,

Ultimately, McAuley imagines that one possible reason we might start modifying ourselves will be because we have no other choice. We’re likely to die in space anyway, so we might as well try something extreme.

Kim Stanley Robinson, another science-fiction author whose work deals with how humans will modify themselves to colonize space, told me that humans will get over the “yuck” factor as soon as we have decent longevity treatments. Once synbio researchers figure out a way to prolong human life, Robinson believes, people will be willing to experiment with their germ lines to create future humans who live for hundreds of years. And once we’ve done that, the floodgates will open. We’ll see humans changing their bodies more radically. We might shrink ourselves into smaller creatures so that we consume fewer resources, or modify our DNA to repair itself after radiation damage in space.

It’s tempting to say that scientists have the right answers here, and that the science-fiction writers are just engaging in rank speculation. But scientists have a duty to deal with strictly present-day scientific knowledge, not futuristic predictions. Sometimes it takes someone who isn’t involved in the day-to-day responsibilities of scientific work to see where today’s research is truly leading.

Getting Rid of Our Bodies

Synbio intervention into evolution may strike us as morally problematic, but it’s a plausible outcome of today’s research. Still, there are many other possible ways humanity might evolve. A group at the Oxford Martin School—where we visited a group of visionary geoengineers in chapter 19—thinks the future belongs to machines. The philosophers who make up the Future of Humanity Institute reside in a set of offices loosely clumped near a meeting room full of conference tables, a wall-sized whiteboard, a coffeemaker, and boxes of slightly odd Scandinavian sweets. Their goal is to explore existential threats to humanity, or extinction-causing events, including many of the dangers we’ve already discussed in this book. But their biggest concern is the possibility that we may be wiped out by “machine superintelligence,” or artificially intelligent computers (AI) that essentially take over the world.

Nick Bostrom heads the institute, where he’s written widely cited articles about everything from human genetic enhancement to existential threats and what he calls “the intelligence explosion.” A Swedish ethicist with closely cropped hair and a perpetually serious expression, Bostrom welcomed me into a spartan office whose windows overlook the courtyard where it’s said J. R. R. Tolkien wrote The Hobbit. When I asked him about humanity’s future, he wanted to get one thing straight right away. If humanity survives, he believes, it’s inevitable that we will pass through an “intelligence explosion” during the next century or two in which we will invent machines with greater-than-human intelligence. Other thinkers have called this event the “Singularity.” These machines will either wipe us out or help us create a future so unlike the present that we can hardly imagine it. But why is it inevitable that we’ll invent AI? “It’s one of those technologies that it’s hard to refrain from developing if we can,” he said. “All the steps up to it have obvious uses. We want better search algorithms, better recommendations from Amazon, and automatic fraud detection. We also want to understand the human brain, for both scientific and medical reasons. It seems hard to imagine how that would stop short of a global cataclysmic event.”

What Bostrom and his colleagues predict is that at some point humans will put together an advanced knowledge of the human brain with the “smart” algorithms that already power services like Google and predictive programs like the ones we’ve seen modeling epidemics and natural disasters. The result, he believes, will be a machine like a human brain with the processing power and memory of an enormous cluster of computers.

Imagine a brain that could process nearly unlimited information and use it to predict possible outcomes to problems and advance scientific knowledge. If such a thing existed, it would dramatically transform humanity—and our relationship to outer space. Bostom put it to me this way. Given that humans are the apex species on the planet due to intelligence, it seems likely that if we invented something with superhuman intelligence it would best us. The question is how, exactly, this besting would occur. Would it become our friendly intellectual older sibling, helping humans to stop pandemics, design the perfect space elevator, and gain superintelligence of our own? Or would it consider humans a bother, the way we do ants? In the latter case, it’s possible the machine’s “fatal indifference” to humanity would end our species forever. It might just kill us accidentally, as it went about its incomprehensibly advanced business.

Assuming we do make it through the intelligence explosion intact, however, Bostrom and his colleagues have a few ideas about what might happen to humanity. Most important to their scenarios is the idea of “uploading,” or turning our brains into software on computers. Our minds could be transferred into virtual worlds, where we would have incredible adventures and expand our consciousness to include the whole of human knowledge. When our bodies died, our uploaded minds would live on—and maybe get downloaded into new bodies. We could also make many virtual copies of ourselves, which is a particularly weird idea that would make perfect sense in a world where you could upload your brain anytime you wanted. Why not save yourself as an upload at different times, the way you do with avatars in a video game, so that you could revert to an older copy if something horrible happened that you’d rather forget? Uploads would completely change our relationships to our bodies and identities, as we easily slid between virtual and biological existence.

Because Bostrom believes this future of superintelligence and uploads is inevitable, he’s convinced that we won’t go to space at all. We won’t want to. Instead, we’ll convert all of outer space into a giant computer running all our uploads in a vast virtual world. His idea hinges on the notion that nobody would want to live in reality anymore when they could upload themselves into a virtual world of plenitude and mental transcendence. So instead of exploring outer space in fantastical vessels, we’d use robots to dismantle every object in space, from planets and asteroids to suns and black holes. Then we’d convert these massive bodies’ every molecule into a giant supercomputer where our uploaded brains could expand forever. In essence, we’d use our superintelligence to convert all of outer space into a vast virtual space for our minds.

What would this look like? Bostrom said, “There’s an image I have in my mind of … a growing sphere, a bubble of technological infrastructure with Earth at the center. It’s growing in all directions at the speed of light.” This growing sphere would be a machine that was converting all matter in the universe into what Bostrom calls “computational substrates,” or computers powerful enough to run a simulation that would satisfy machine superintelligences. In a sense, it would be like paving over the universe with our computers. “Most likely, everybody would live in virtual reality, or some abstract reality,” Bostrom concluded. Space would be ours, but only because we converted every piece of matter into our high-tech brain farm.

But, to continue the paving analogy for a moment, what if there was life using some of that matter in the universe? Wouldn’t we be destroying it to build our virtual world? Bostrom is unperturbed by this possibility. “My guess is that our observable universe doesn’t contain intelligence, so we don’t need to worry about taking matter away from them.” His main concern is what’s going on inside that sphere of technology he imagined hurtling out of the Earth. What if it were a version of the Windows operating system, but with superintelligence? In a dark scenario, “we might all be paperclips or calculating pi to millions of decimals,” he mused. But in a brighter one, we might be liberated from our bodies, evolving beyond death in a virtual world of our own devising. We’d have become beings who explore inner space rather than outer space.

One of Bostrom’s colleagues at the institute, Anders Sandberg, was less certain that our future would be purely virtual. A gregarious man who loves science fiction, he talked just as eagerly about role-playing video games as he did about the medallion around his neck that contains instructions on how to freeze his head cryogenically in the event of his death. Sandberg shares Bostrom’s belief in the intelligence explosion, allowing, however, that we might venture into outer space afterwards. But, he asserted, “having a biological body in space is stupid in many ways.” He suggested we might become more like cyborgs, mechanical creatures controlled by uploaded human brains. This would protect us from radiation damage, the need for food, and many other tribulations of space travel and colonization. “Uploading is just a more flexible way of living,” Sandberg explained. He suggested that we might solve the problem of how long it takes to travel in space by loading the crews’ brains into software for the decades or centuries it would take to reach their destination. Once the ship arrived, those brains would be downloaded into whatever bodies might suit the planet where we arrived. Maybe those bodies would be part technological and part biological. Or they might be biological forms ideally suited for life on a world like Titan, with methane gas for atmosphere.

Excitedly mulling over our future bodies, Sandberg pointed out that living part time as software might ensure humanity’s long-term survival in other ways. It could keep humanity safe from a pandemic, for example. “It’s also about enhancing adults,” he pointed out. “It’s ethically less problematic than genetically engineering our children.” So turning into machines, losing our bodies forever, may cause fewer moral quandaries than modifying our genes but keeping our bodies.

Evolution Stops for No One

Even if we don’t genetically alter or upload ourselves, we will nevertheless evolve into a different sort of creature in the next million years. Many evolutionary biologists believe that humans are still evolving. The University of Chicago geneticist Bruce Lahn has demonstrated that some of our genes, like those controlling brain size, appear to be undergoing very rapid selection. And researchers in Finland have pored over the family histories recorded in a Finnish village church, and discovered clear patterns of natural and sexual selection emerging over a period of centuries among the locals. When I spoke to Oana Marcu, a SETI Institute biologist who researches how life first evolved, she emphasized strongly that we aren’t the end results of billions of years of evolution. We are still in the middle of an evolutionary journey, with many changes ahead of us.

When we begin heading out into space, evolutionary pressures will select for humans best able to survive in our new environments. If there’s one thing we know for sure about evolution, it’s that a change in environment often leads to dramatic changes for species. It also leads to speciation. If humans spread out to many planets and moons, those groups may begin to diverge genetically after millennia have passed. No matter what scenario you think is most likely—synbio, uploads, or natural selection—our progeny may look nothing like us. But they will still be part of humanity, and they will carry in them our profound, seemingly unquenchable urge to explore new environments and adapt to them as best we can.

ONE MILLION YEARS ago, our ancestors thought it was pretty fantastic to have fire and flake tools. One million years from today, humans could be living in lakefront communities on Saturn’s moon Titan, using technologies that make our rocket fuels and supercomputers look like a Homo erectus tool kit. Astronomers often point to Titan for possible colonization because it has a thick atmosphere that could offer us some of the protection from radiation that Earth’s does. Plus, it has weather very much like Earth’s, with seasonal rains and snows. On Titan, there are beaches full of dunes, shimmering great lakes, and the occasional volcano. Except that the volcanoes erupt with ice and the lakes are made of methane. The spring showers are methane, too. In short, it’s a place that would freeze and poison any human on Earth today. But what if, in a million years, we’d engineered humans to survive there? Maybe they would be fitted with lung implants that could convert local gases to a mix that would oxygenate their blood. They might be uploads running robotic exoskeletons, or biological beings built from genetic parts that allowed them to thrive in Titan’s atmosphere. Or they might have terraformed the moon to suit human bodies.

If our progeny do make it that far, it will be because humanity has chosen exploration over warfare often enough that we’ve managed to work together as a planet on several large projects. One of those projects would be pushing our species off this rock, scattering us through the solar system. This project is important for reasons that go beyond how great it would be to fly through Saturn’s rings. It’s also important as a long-term human goal because most of the steps that lead to its realization will take us down the pathway of survival rather than death.

Planning for Life Beyond Earth

“Our kids are the last generation who will see no city lights on the Moon,” the NASA Jet Propulsion Lab’s Randii Wessen told me when we talked about the economic feasibility of space travel. Though his prediction isn’t outside the realm of possibility, we should also think pragmatically about the path to space. Wessen’s colleague the atmospheric physicist Armin Kleinboehl is far more conservative in his estimates of when humans might live beyond Earth. Kleinboehl studies Martian weather via the Martian Reconnaissance Orbiter (MRO), a craft that has been photographing and analyzing the Martian surface from orbit since 2006. When we met, he showed me some MRO images of dust storms that periodically envelop all of Mars, making it even colder than it is normally. When I asked Kleinboehl what he thought the timeline might be for a Mars colony, he frowned and glanced over at a video simulation of Martian weather. “It won’t be attractive for at least five hundred years,” he said finally. “It’s not very hospitable.” When I asked about terraforming, Kleinboehl conceded that that was one way Mars might eventually become habitable. Perhaps we could cultivate plants or bacteria on Mars that photosynthesize, pop out free oxygen, and change the environment.

Though it’s popular to imagine that humans will be exploring the galaxy in Star Trek style over the next couple of centuries, this leap may take a little longer. And that’s good news. By the time we’re ready to set up tourist resorts on Titan, we may have reached the point as a civilization that we won’t “fuck everything up,” as synbio designer Daisy Ginsberg so succinctly put it.

It’s not very popular to suggest that the future could happen slowly, or that tomorrow’s scientific innovations might take as much time as they have historically. Futurists like Ray Kurzweil are fond of suggesting that the pace of discovery is “accelerating,” and that change will move at a blindingly rapid clip over the next century. While anything is possible, we shouldn’t expect immortality, superintelligence, and faster-than-light travel in our lifetimes. Anticipating instantaneous, radical change diverts us from investing time in long-haul projects like building safer, sustainable cities and planning for food security. These are the kinds of scientific endeavors that can help us survive while we’re waiting for somebody (or something) to invent upload technology. I’m not suggesting that we should slow down the pace of scientific discovery. Quite the opposite. I’m saying we should focus our scientific and technological energies on problems that are solvable in the near term, while always keeping our eyes on the long-term goal of exploring and adapting to worlds beyond our blue marble.

If we’ve learned anything from the survivors among our ancestors, it’s that staying put and fighting change are not good tactics if we want to live. Survivors range over vast regions. If they encounter adversity in one environment, they try to escape and adapt to a new environment. Survivors prefer the bravery of exploration to the bravery of battle. But present-day humans differ dramatically from most of Earth’s survivors in one crucial way. We can make plans for the future. And with the help of scientifically informed models, we can also consider how we would deal with many possible future scenarios. What if an asteroid hit? A flood? A plague? A drought? Right now, we have many excellent ways of figuring out how each of these species-ending disasters might unfold—and we have ways of preventing most of them from killing us all.

Surviving is partly a matter of implementing what we already know. But it’s also about planning to deal with disasters we know for certain aren’t survivable right now. Those are the kinds of disasters that require us to build cities on Mars, Titan, Europa, the Moon, asteroids, and any other uninhabited chunk of matter we can find. The more we explore, the more likely it is that our species will make it.

The Right Path

Perhaps no research plan expresses this idea better than the 100 Year Starship, a project run by the doctor and former astronaut Mae Jemison. The project, initially funded by the U.S. government, is now a nonprofit organization whose goal is to develop a starship capable of bringing humans to another star system. It’s called 100 Year Starship because Jemison and her colleagues estimate that it will take roughly a century to develop the technology. Though this time period is short compared with the million-year view I was just describing, it’s still longer than pretty much any other scientific project currently under way. I asked Jemison why she had set a goal beyond her lifetime and that of anybody working on the project now. It was both pragmatic and necessary, she said. The technologies needed are far beyond our current levels of development. And, she added, we need time “to create a movement here on Earth, imbuing society with the aspiration to get this accomplished.” Calling the mission “optimistic,” she added that she and the scientists associated with the project will be developing several technologies along the way to their goal which could be useful in themselves. Perhaps they’ll create a better kind of propulsion, or new hydroponic systems for growing plants in space. “Weightlessness could be a platform,” she mused, where we could stage any number of experiments before taking off for the next habitable star system. Her point also holds true for the science we’ll develop as we prepare to build a space elevator and an asteroid-nudging fleet—it may help us back on Earth.

One of the scientists already studying what life might be like elsewhere in our solar system is the planetary scientist Nathalie Cabrol. She conducts missions for the SETI Institute, where she studies remote environments on Earth that are similar to environments we might find on Mars, Titan, or Europa. In the rocky peaks of the Andes mountains, where the atmosphere is thin, she and her team dive deep into lakes whose chemical compositions are rare for earthly bodies of water. There, Cabrol told me that they look for the kinds of life that could thrive on another world; they also try to figure out what would survive if Earth underwent a radical environmental change. Cabrol’s team is making discoveries that are relevant for the near future and the far future. And in the process, they may discover something totally unexpected.

Cabrol explained that one of her current projects is to develop a robotic rover that could land on an unexplored world—like, say, in the oceans of Jupiter’s moon Europa —and figure out what it should be studying. Because the robot would be on a totally new world, it would need to be able to get a baseline for what was normal there, and then judge what aspects of the environment were extraordinary or worth studying in greater detail. To explore Europa, in other words, we have to build a robot that can think like a scientist, taking in data and deciding which pieces of that data are salient. Work like Jemison’s and Cabrol’s led the celebrated science historian Richard Rhodes to speculate at the space exploration conference SETICon in 2012 that one unintended consequence of space exploration might be the emergence of artificial intelligence. So Nick Bostrom’s intelligence explosion could happen on Europa rather than on Earth.

What’s important is that the move into space sets humans on a journey that’s survivable. And it’s one that might yield many incredible discoveries along the way. Jemison, who told me she’s a fan of Octavia Butler’s writing, emphasized that she hopes the 100 Year Starship project will help humanity grapple with social as well as scientific issues. “What does it mean to be an interstellar civilization?” she asked. “What are the philosophical implications?” When I pushed her to answer those questions, however, Jemison did something very unexpected. She refused to speculate.

“The reason why is that if I speculate now, I can’t keep a blank whiteboard in front of me,” she explained. “As a person who is leading this, I don’t want to say, ‘When we get there it has to be this way.’ It may be totally different from what we expect.” By keeping her whiteboard blank, as it were, Jemison provides a model for what it means to plan for the future without foreclosing any possibilities. We can create maps and guides without locking ourselves into any particular outcome. The journey to the stars may take many forms. It may take centuries. But while we’re waiting and researching and designing our starships, we can build a civilization that’s sustainable back on Earth.

What Will They Remember About Us?

As we start our journey into the next million years, it’s useful to ask what you hope your progeny will remember about Homo sapiens. What do you want it to mean when they call themselves “human”? When I think about my post–Homo sapiens offspring, frolicking with their robot bodies in the lakes of Titan, I hope they remember us as brave creatures who never stopped exploring. What unites humans of the distant past with our possible future kin is an ability to survive adverse conditions by splitting into distant but connected bands. And what makes us human is our ability to build homes and communities almost anywhere. We should treasure this skill, because it is the cornerstone of our best survival strategy. We’ll strike out into space the way our ancestors once struck out for the world beyond Africa. And eventually we’ll evolve into beings suited to our new habitats among the stars.

Things are going to get weird. There may be horrific disasters, and many lives will be lost. But don’t worry. As long as we keep exploring, humanity is going to survive.