Oldest evidence for animal life found in rocks from India

Researchers found a steroid compound produced only by sponges

Researchers have found the oldest clue yet of animal life in ancient rocks and soils, including those from India, dating back at least 100 million years before the famous Cambrian explosion of animal fossils.

Researchers at the University of California, Riverside, United States, tracked molecular signs of animal life, called biomarkers, as far back as 660-635 million years ago during the Neoproterozoic Era.

In ancient rocks and oils from India, Oman and Siberia, they found a steroid compound produced only by sponges, which are among the earliest forms of animal life.

‘Thriving in ancient seas’

The ‘Cambrian Explosion’ refers to the sudden appearance in the fossil record of complex animals with mineralised skeletal remains 541 million years ago.

“We have been looking for distinctive and stable biomarkers that indicate the existence of sponges and other early animals, rather than single-celled organisms that dominated the Earth for billions of years before the dawn of complex, multicellular life,” said Alex Zumberge, a doctoral student at UCR.

The biomarker they identified, a steroid compound named 26-methylstigmastane (26mes), has a unique structure that is currently only known to be synthesised by certain species of modern sponges called demosponges.

“This steroid biomarker is the first evidence that demosponges, and hence multicellular animals, were thriving in ancient seas at least as far back as 635 million years ago,” Zumberge said.