Animals, not catastrophe, caused first mass extinction

The rise of early animals, not meteorite impacts or volcanic eruptions, led to the world's first known mass extinction, which took place about 540 million years ago, suggests new research.

While mass extinctions are generally associated with catastrophic events, like giant meteorite impacts and super volcanoes, the new study puts the blame on the emergence of complex animals that can change their environment.

"People have been slow to recognise that biological organisms can also drive mass extinction," said Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University in Tennessee, US.

"But our comparative study of several communities of Ediacarans, the world's first multicellular organisms, strongly supports the hypothesis that it was the appearance of complex animals capable of altering their environments, which we define as 'ecosystem engineers,' that resulted in the Ediacaran's disappearance," Darroch said.

Researchers believe that earliest life on Earth consisted of microbes - various types of single-celled micro-organisms. They ruled the Earth for more than three billion years.

Then multi-cellular organisms like Edicarans emerged and in their heyday,they spread throughout the planet. They were a largely immobile form of marine life shaped like discs and tubes, fronds and quilted mattresses.

After 60 million years, evolution gave birth to another major innovation: animals.

Animals burst onto the scene in a frenzy of diversification that palaeontologists have labelled the Cambrian explosion, a 25-million-year period when most of the modern animal families - vertebrates, molluscs, arthropods, annelids, sponges and jellyfish - came into being.

"These new species were 'ecological engineers' who changed the environment in ways that made it more and more difficult for the Ediacarans to survive," Darroch said.

The researchers performed an extensive palaeoecological and geochemical analysis of the youngest known Ediacaran community exposed in hillside strata in southern Namibia.

The site, called Farm Swartpunt, is believed to be 545 million years old.

Having ruled out any extraneous factors, Darroch and his collaborators concluded that "this study provides the first quantitative palaeoecological evidence to suggest that evolutionary innovation, ecosystem engineering and biological interactions may have ultimately caused the first mass extinction of complex life."

The researchers believe that as humans are the most powerful 'ecosystem engineers' ever known", an analogy between the Earth's first mass extinction and what is happening today can be drawn.

The study was published in the journal Proceedings of the Royal Society B.