The discovery of fossils from the Cambrian period almost 545 million years ago, prompted scientists to think the idea that this period may have been a genetic or environmental catalyst of early animal evolution.

The Cambrian Period marked an important point in the history of life on earth; it was the time when most of the major groups of animals first appeared in the fossil records. This event is sometimes called the "Cambrian Explosion", because of the relatively short time over which a diversity of forms appeared.

During the Cambrian, the land was probably just about lifeless. Even fishes didn't exist yet. But there were many marine invertebrates that would look familiar today, including sponges and bivalves. But the best known Cambrian animals are probably a group of armored creatures that no longer exist—trilobites.

These early fossil record suggests that exceptional evolutionary activity took place over 10 million years at the time of the Cambrian period and generated the ancestors of nearly all the animal groups living on Earth today, as well as others that failed to see modern times like the dinosaurs.

In the geological time, the first known multi-cellular life shows up in the fossil record around 570 million years ago, in the Precambrian period before the Cambrian period. All living things on earth at this time lived in the sea, as we might expect, because life originated in the sea and it took it a long time to work out ways of moving onto the land.

Most organisms back then were single-celled, just as most organisms are today and consisted of bacteria, algae, and soft-bodied animals like jellyfish and worms. But the multi-cellular life of the Precambrian doesn't look much like anything we find in our modern oceans. Most of the large Precambrian organisms were built on a body plan unlike anything alive today. They were flattened mats of pasted-together tubes, spreading outward from a central core or axis, and in cross-section, they looked like an inflatable air-mattress.