Researchers find earliest evidence of animal life

Chemical traces found in sedimentary rocks more than 635 million years old are the oldest evidence in the fossil record of the appearance of animal life, scientists said Wednesday.

The evidence, found in the shallow coastal waters of what is now Oman, were fossilized remains of compounds, called steranes, which are produced by marine demosponges.

Demosponges are one of the simplest forms of multicellular animals, and live in both coastal waters and in the deep sea today.

The chemical traces discovered are the hydrocarbon remains left over from the cell membranes of the sponges, and helped provide the membranes with structural support when the sponges were alive. The sponges themselves were just a few millimetres in size, immobile and fed on dissolved and particulate organic debris.

Scientist Gordon Love of the University of California at Riverside and colleagues from MIT published their findings this week in the journal Nature.

Love said the discovery not only pushes back the date of the first known appearance of animal life, it also adds further detail on how that life may have started in shallow waters and later spread to the seafloor.

Scientists have ample evidence of the diversification of life around 530 million years ago, during a period known as the Cambrian explosion, but have far fewer details on the different forms of life before then.

"We believe we are converging on the correct date for the divergence of complex multicellular animal life, on the shallow ocean floor between 635 and 750 million years ago," said Love in a statement.