Wonders of the Universe - Brian Cox [31]
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.
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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.
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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