PROLOGUE

We think of the underworld as a place for the dead. Yet beneath our feet teems a world of life more vibrant, diverse, mysterious, and resilient than anything clinging to Earth’s fragile exterior.

Our deepest drills, boring a mile below the ocean floor, found life. Three miles down the shaft of a South African gold mine, life was waiting for us. Even inside a body of water the size of Lake Ontario locked two miles under the surface of Antarctica, researchers found an entire ecosystem of life they never imagined.

In the depths of the Earth dwell organisms impervious to boiling heat, freezing cold, intense radiation, toxic salinity, noxious gases, extreme pressure, and total darkness. Far from fragile, these communities of extremophiles have proved themselves hardier than any surface life in the temperate zones that we call home.

Indeed, after sampling the depths of our planet, scientists now believe that even cataclysmic impacts from extraterrestrial bodies could not eradicate life on Earth. Subterranean species would undoubtedly survive. Life might even have endured the death of other planets and traveled trillions of miles inside meteors to seed our islands and seas, resulting, three-and-a-half billion years later, in scientists who question life’s endurance.

With all the shifting, layering, and folding of our planet’s geology, the variety of microorganisms evolving inside its crust must be impossible to guess. Whole worlds separated by an inner space of solid rock have been adapting for millions and billions of years, each in entirely unique conditions. Most organisms in these isolated ecosystems grow very slowly, some dividing only once a century. Others devour rock and, over geological ages, they have created some of the world’s largest cave systems.

When exposed and then sealed, caves capture samples of life from the surface and carry them forward on diverging evolutionary pathways across inconceivable spans of time. The Movile Cave in Romania, isolated five million years ago, contains today thirty-three species found nowhere else. A recently unsealed cave in Israel revealed unique shrimps and scorpions whose ancestors must have entered from the former Mediterranean shore millions of years ago. Newly discovered caves of Sequoia National Park revealed twenty-seven new species, some of which had evolved to live in only one room of the cave.

Over a quarter of a million caves have been documented, so far, and the number grows more rapidly each year. Humans have explored only a fraction of these subterranean worlds, each of which contains a different atmosphere of gases, a unique mix of minerals, and a collection of species that have adapted to its conditions descending from different epochs in our planet’s history.

And yet, for all the exotic species that we know must dwell beneath the Earth, the species closest to the underworld, both physically and spiritually, may be us.

Researchers excavating a South African cave recently discovered evidence that our “caveman” heritage stretches back at least two million years. Caves were, indeed, the cradle of mankind.

Stone Age Europeans and ancient peoples in the Americas frequented caves that stretch for miles, as modern-day spelunkers have discovered to their astonishment. Such dangerous journeys were undertaken for mysterious purposes, and certainly not practical ones, suggesting a fearless fascination with the infernal regions that may run deep in our psychological heritage.

During their long Stone Age, humans accumulated an intimate knowledge of Earth and its layers that would lay the foundations of our future progress. Along the way, the fossils borne up by the earth were like bas-relief friezes of gods and monsters. The odd shapes they saw in the stones, spiraling symbols and complex forms, leaped out of the rock like words into the brains of primitive hominids. The fossil record of the Earth was a premonition of art, mythology, and geometry. We now know that Neanderthals were the first to paint symbolic animals on a cave wall, and we know that they collected fossils. These first paleontologists actually sorted them by species like religious relics. The pages of Earth’s own history book thus instructed our ancestors’ intellectual evolution.

As far back as 15,000 B.C., in Turkey, humans began to modify caves. And it is there that centuries later cave dwelling reached its apex in the underground cities of Cappadocia.

Over the course of the Stone Age, accident and insight fused fire with rock. And at the end of that long precursor to human history, the principles of metallurgy emerged. The smelting of ore produced copper, equipping humans with tools that could cut limestone and construct the pyramids that mimicked mountains riddled with tunnels and caves. Bronze forged from the earth enabled men to chisel marble into cavernlike temples supported by stalagmite pillars of marble built of disks resembling the fossilized vertebrae of crinoids.

We left our caves behind for freestanding dwellings aboveground, and yet we humans have continued to return to the underworld long after to mine its mysteries and treasures. With new technology, our species has drilled and blasted vast subways for us to travel beneath Moscow, New York, London, San Francisco, Paris, and Hong Kong. Whole underground cities have been carved under Seattle, Montreal, Sydney, Buenos Aires, Santiago, Beijing, Kish, Osaka, Tokyo, Kawasaki, and Nagoya, and they are currently occupied by millions of people every day. Yet even these titanic excavations shrink before the future engineering projects already grinding their way into our planet’s crust.

Particle accelerators that spare the surface from the consequences of quantum physics, sensors buried deep under mountains to detect cosmic rays, earthquake sensors miles beneath the ocean floor, and even more ambitious underground engineering projects to divert surface floods, span channels, cross mountain ranges, or hide secret military operations are under way around the globe every day. Deep oil-drilling techniques will soon bore five miles into the Earth’s crust and, as oil grows ever more scarce, drill ever deeper.

We know we are not the only exotic creatures expanding their niche in the vast inner space beneath us. Whatever the earth yields up, whatever its shape, story, and strategy, it will certainly prove more incredible, perhaps more infernal and diabolical, than all the myths our ignorance has conjured.

—from the afterword of The Underground History of Planet Earth by Anastasia Kurolesova, Moscow Geological Institute Press

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