Life 'explodes'

Trilobite fossils

Life became more diverse and abundant in the seas during the Cambrian time period, which started about 545 million years ago. Fossils in Pre-Cambrian rocks are of simple life forms such as bacteria, with more complex soft-bodied creatures appearing towards the beginning of the Cambrian. Cambrian rocks show large numbers of many different types animals, many with hard shells.

This important shift is often described as an "explosion", but new evidence suggests that it may have been a more gradual change. Part of the difficulty is that the fossil record is not complete - some life forms were more likely to be fossilised than others, and the conditions that allow fossilisation to occur were also not constant.

Image: Trilobite fossils. Trilobites appeared on Earth during the Cambrian period. (credit: Sinclair Stammers/SPL)

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Trilobite fossils Life 'explodes'

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Life 'explodes'

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