EASY READ Prehistoric life
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What were the first living things?
The first living things probably appeared in the oceans about 3.8 billion years ago. They were tiny life-forms called bacteria. It took another 2.5 billion years before more advanced life-forms, types of seaweed, started to appear. Living things that we might describe as animals, soft-bodied sea creatures such as jellyfish, appeared around 680 million years ago. Worm-like creatures appeared about 600 million years ago.
Cambrian explosion
The first animals with hard parts—shells or bony skeletons—first appeared about 539 million years ago. This was at the beginning of a time in the Earth’s history that scientists call the Cambrian Period. A wide variety of living things appeared. It was like an “explosion” of life.
These animals lived in warm, shallow seas. They included shellfish, corals, starfish, molluscs and sponges. Some very strange-looking animals swum in the Cambrian seas. One, Opabinia, had five mushroom-shaped eyes. The largest and fiercest of all Cambrian creatures was the 60-centimetre (24-inch) Anomalocaris. Its name means “odd shrimp”. It had two large eyes set on stalks and a pair of pincer-like arms.
Our ancestor?
One of the creatures swimming in the Cambrian seas, called Pikaia, appeared to be half-worm, half-fish. It had short tentacles on its head and swam perhaps like an eel. Scientists think it could have been an ancestor of all backboned animals (vertebrates), including fish, reptiles, birds and mammals.
Consultant: Chris Jarvis
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Precambrian and Cambrian
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