Animals older than we thought

Go back around five hundred and forty million years ago, and you'll get to the end of the Neoproterozoic era, a time of climate extremes and phenomenal bursts of evolution that culminated in the emergence of the very first animals - our ancient ancestors.

Now new results from a collaborative team of researchers from the US, Australia and the UK pushes back the origin of animals to further than 635 million years ago, before the end of a major ice age called the Marinoan glaciation.

Writing in this week's edition of the journal Nature, the researchers looked for the presence of specific chemicals in rockas na doils deposited in the fossil record, known as C30 sterols. These are steroid chemicals produced by very primitive ancient sponges, called demosponges, that are thought to be one of the very earliest forms of animal.

They found high levels of these C30 sterols in an area called the South Oman Salt Basin, at the southeastern tip of Arabia, which contains fossil deposits from the Marinoan glaciation period, which ended around 635 million years ago.

These levels are comparable to those found in sites containing animal fossils from a much later period. So this suggests that animals, in the form of these little sponges - were around much earlier than we previously thought. There's already evidence of sponge fossils from around 540 million years ago, but this discovery marks the oldest known animal life.

The researchers pinpoint the development of animals to the Cryogenian period, which is roughly 850 to 635 million years ago. Their analysis showed that the oldest the sponges could possibly be were 750 million years old. So these new results put the evolution of animals somewhere between those two dates.