Complex life evolved on Earth 100 million years later than previously thought, say scientists

The first signs of complex multicellular life evolved on Earth about 100 million years later than expected, according to scientists studying chemical biomarkers.

Researchers at the Australian National University (ANU), the Max Planck Institute and Caltech say this finding has big implications for our understanding of evolution.

A 2009 MIT study claimed that the first complex life evolved 635 million years ago – based on traces of chemicals found in rocks in Oman that date back to this period.

The chemicals found in the rocks – including steroids – were remarkably similar to chemicals produced by modern sponges and therefore were assumed to be biomarkers for complex life.

A team of chemists were able to recreate the same “biomarkers” in a laboratory using common algae, widely present on Earth during this period.

Animals quickly diversified and became ecologically dominant in the early Cambrian Period (541 to 485 million years ago) – yet scientists believe the first animals must have arisen much earlier than that based on molecular data.

Many suspect they may have emerged during the Neoproterozoic Era (1,000 to 541 million years ago), although the exact timing remains controversial.

The oldest uncontroversial animals in the fossil record are found in deposits from 558 to 552 million years ago during the Ediacaran period and others, with “some degree of confidence”, date back to 571 million. years.

However, most molecular clocks place the appearance of animals between 900 and 635 million years ago – during Cryonian or Tonian periods.

The researchers used “biomarkers” to try to bridge the 340 million year gap between the molecular clock and actual fossil evidence.

That’s what the MIT team did in 2009 when they found “ evidence ” for a sponge biomarker in rocks dating back 635 million years – but new research has revealed that these biomarkers could be produced by other mechanisms – not just sponges.

“This brings the oldest animal evidence closer to 100 million years old today,” said Dr Lennart van Maldegem, co-author of one of two related studies on the potential origins of biomarkers in these. ancient rocks.

“We were able to demonstrate that some common algal molecules can be altered by geological processes – leading to molecules that cannot be distinguished from those produced by sponge-like animals.”

This brings the first “ confirmed ” date for the start of complex life on Earth to around 560 million years ago – for sponges living in Cambrian times.

The mystery of when our very first animal ancestors emerged and became abundant in the oceans has puzzled paleontologists for over a century.

“Ten years ago, scientists discovered the molecular fossils of an animal steroid in rocks that once lay at the bottom of an ancient Middle Eastern sea,” said Prof Jochen Brocks, co-author of study.

“The big question was, how could these sponges have been so abundant, covering much of the seabed across the world, leaving no bodily fossils behind?

Dr Ilya Bobrovskiy, lead author of the other study, said the researchers were able to “solve this mystery” by recreating the steroid markers in the lab.

“While it’s true that sponges are the only living organism that can produce these steroids, chemical processes can mimic biology and turn common and abundant algal sterols into ‘animal’ sterols,” he said. declared.

“These molecules can be generated in the laboratory when simulating geological weather and temperatures, but we have also shown that such processes occur in ancient rocks.

Both studies were published in Nature Ecology and Evolution.