Wonders of the Universe

FIRST SIGHT

Hidden in the high Rocky Mountains in British Columbia, Canada, is one of the most important and evocative scientific sites on Earth, and it’s where the story of light and our lives begins. Around 505 million years ago, when this whole area lay deep beneath the surface of a primordial ocean, it was hit by a huge mudflow. The mud buried everything in its path and created a snapshot of a remarkable time in the evolution of life on Earth. A whole ancient ecosystem was frozen and preserved intact in the mud; the lives of the primitive creatures documented by a chance geological event with the care and precision with which the Egyptians created their glorious tombs half a billion years later. For hundreds of millions of years, this ancient treasure trove was locked away, but in 1909 it was uncovered high on a mountainside. This is the Burgess Shale.

The Burgess Shale is one of the most important fossil sites in the world. It is not just the number and diversity of the animals found here, it’s their immense age. Before around 540 million years ago, there are no fossils of complex life forms found anywhere on the surface of Earth. We know that there was life before this period, but the animals were very simple creatures that didn’t possess skeletons of any kind. This means that they don’t show up on the fossil record. In the geological blink of an eye in the period of time immortalised in the Burgess Shale, known as the Cambrian Era, it appears that a vast range of complex multi-cellular life emerged on the planet. Biologists call it the Evolutionary Big Bang, or the Cambrian Explosion.

One current theory for the origin of the Evolutionary Big Bang is that the emergence of the eye in animals such as the trilobite triggered the Cambrian Explosion. Once one predatory species develops eyes, there is a powerful selection mechanism in favour of others developing and refining eyes too.

Numerous genera of trilobites have been found in the Burgess Shale. These fossils are so detailed and well preserved that they have enabled scientists to make important observations about the structure and behaviour of these now-extinct organisms.

So what triggered the evolution of complex life? There is a clue in these fossil beds that lie high in the Canadian Rocky Mountains. The picture left shows one of the ancient animals found here; a complex organism called a trilobite. Trilobites, now long extinct, had external skeletons and jointed limbs, but most strikingly they had complex, compound eyes. These prehistoric predators could see shapes, detect movement and use their eyes very effectively to chase their prey. The ability to see made these trilobites very successful animals indeed; in fact they survived for a quarter of a billion years, only vanishing from Earth in the Permian mass extinction 250 million years ago.

One current theory for the origin of the Evolutionary Big Bang is that the emergence of the eye in animals such as the trilobite triggered the Cambrian Explosion. Once a predator possesses eyes which will help it chase its prey, a new force in natural selection is immediately introduced. The animals that survive this selection are those that are best adapted to this new threat; they may camouflage themselves, leading to an increasingly sophisticated visual appearance, or dodge the predators with enhanced sense organs. In other words, once one predatory species develops eyes, there is a powerful selection mechanism in favour of others developing and refining eyes too. In turn, this selects far more sophisticated predators, and so on. This is in a sense an evolutionary arms race, as the pressure of natural selection leads more and more complex life forms to develop.

The Carina Nebula is a large bright nebula that surrounds several clusters of stars. It contains two of the most massive and luminous stars in our Milky Way galaxy, Eta Carinae and HD 93129A. Located 7500 light years away, the nebula itself spans some 260 light years across, about seven times the size of the Orion Nebula, and is shown in all its glory in this mosaic. It is based on images collected with the 1.5-metre Danish telescope at ESO’s La Silla Observatory.

NASA

These early creatures, immortalised in the Burgess Shale, were among the very first to harness the light that filled the Universe. Before they emerged, the rise and fall of the Sun and the stars in the night sky went unnoticed. These creatures are our ancestors, and in fact there is also evidence at Burgess that we humans may only exist because of one particular adaptation in a strange, worm-like creature called a Pikaia. Although the Pikaia looks unimpressive, it may be one of the most important animals ever discovered. It is thought by some, although not all, evolutionary biologists that the Pikaia is the earliest known ancestor of modern vertebrates – the branch of life that we are categorised in – so it could be that this little worm-like creature is our earliest known ancestor. What is also fascinating about Pikaia is that it may have had light-sensitive cells that allowed it to evade predators and survive in the Cambrian seas – cells that may have evolved over many hundreds of millions of years into our eyes. This is all speculative, but it is possible that without Pikaia’s primitive yet remarkable ability to detect the light from the Sun, we humans may never have appeared on planet Earth. Perhaps there would never have been a life form here with the ability to do the one thing that has allowed us to understand our universe more than anything else: to look up.

We have even been able to capture the light from the beginning of time and we have glimpsed within it the seeds of our own origins.

Understanding the Universe is like reading a detective story, and the essential evidence we need to solve it has been carried to us across the vast expanses of space and time by light. We have even been able to capture the light from the beginning of time and we have glimpsed within it the seeds of our own origins. We’ve seen things our ancestors wouldn’t believe: stars being born in distant realms, and galaxies lost in time at the very edge of the visible Universe and our cosmos just moments after it all began.

It’s a wonderful thought that these primitive biological light detectors that emerged on Earth half a billion years ago in the Cambrian Explosion have evolved into those most human of things; our green, blue and brown eyes that are able to gaze up into the night sky, capture the light from distant stars and tell the story of the Universe