Bill Bryson Chapter 21- Life Goes On - Josh Smithson

Fossilisation is an extremely rare occurrence, less than 0.1 percent of all living organisms become fossilised, and Only about one bone in a billion ever becoming fossilised. About 95 percent of all fossils are from animals that once lived in the water, so it is very unlikely for a land animal to become fossilised.

Richard Fortey studies trilobites, an organism with three main body parts - head, tail and thorax. Trilobites first appeared about 540 million years ago in what is known as the Cambrian explosion, a great outburst of complex life. Trilobites were around for 300 million years before dying out.

A paleontologist named Charles Walcott was the first person to discover that trilobites are anthropods, a group that includes insects and crustaceans. Walcott also discovered the Burgess shale, a large array of unturned fossils that no one had seen before containing over 140 species, making it one of the greatest finds in paleontology history.

One of the fossils found in the Burgess Shale was a worm like creature called pikaia gracilens. It had a spinal column making it the earliest known ancestor of all vertebrates, including humans.

Over the years there have been many scientists such as Stephen jay Gould and Reginald Sprigg have been able to overturn the idea of the Cambrian explosion with findings of complex creatures from millions of years before the so called Cambrian explosion. The explosion wasn't an appearance of complex life, but rather a growth in the creatures found.