When did the first animal appear on earth?

During the Silurian era the first simple animals began to appear on land. It is thought that this is due to the development of the Ozone layer protecting non-aquatic life for UV radiation. (This refers to the appearance of animals on dry land. Animals in the sea existed long before.)

In the late pre-cambrian multi-cellular life appear in the sea due to the presence of high oxygen level in the atmosphere.

Here is another:

A small micro organism, having single cell born in sea, it had characteristics of both plant and animal. Hence it is the first plant as well as first animal. Some millions of year back.

The first known fossils of what is possibly animal life appear in the Ediacara biota just prior to the Cambrian era. ca. 635-542 Ma

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