A massive asteroid that struck South Australia during a glacial cold snap 590 million years ago may have triggered the evolution of Earth’s earliest complex organisms, Australian geologists reported. In 2010, researchers from the University of Adelaide argued that the Acraman asteroid impact coincided with an extensive glaciation period more than 500 million years ago and created ideal conditions for an explosion of complex organisms, known as the Ediacara biota.
“Release from the combined environmental stresses of a frigid, glacial climate near sea level and a major impact in low latitudes may have been a factor influencing subsequent Ediacaran biotic evolution,” geologist Victor Gostin and colleagues wrote in their paper in the Australian Journal of Earth Sciences.
Originating several million years after the asteroid impact, the Ediacarans are an enigmatic assemblage of multicellular organisms, many of which bare scant resemblance to anything alive today. The first Ediacaran fossils were discovered in the Flinders Ranges in South Australia, 300 km east of the Acraman Impact site.
The Acraman asteroid impact has been the subject of a vast body of research, but this latest study provides evidence that ice may have covered much of the planet - the snowball earth hypothesis - when the asteroid struck.
Gostin and colleagues discovered glacial debris - pebbles and gritty sediments left by floating ice - among the shattered rocks flung out more than 500 km from the impact site. It suggests that the impact occurred during a low-latitude glaciation period, rather than precipitated one as previously proposed.
The impact of the asteroid, which had the energy of 5.2 million tons of TNT, would have been cataclysmic in scale, causing widespread earthquakes, tsunamis and fires. It had a devastating effect on life on earth, which was already enduring the stresses of a severe cold snap.
According to Gostin, the evidence that important changes took place in the biosphere around the time of the Acraman impact event comes from fossil pollen, carbon isotopes and biomolecular data. “These involve the collapse in primary productivity and the subsequent appearance and diversification of large complex acritarchs (microfossils) and multicellular animals (the famous Ediacaran fossils),” Gostin said.
Astrobiologist Malcolm Walter, from the University of New South Wales in Sydney in an interview with Cosmos Magazine compares it to the rapid diversification of mammals that followed the demise of the dinosaurs, but raises his own question: “What went extinct [before the Ediacara biota]? What we seem to see is the other side of the coin, a recovery event, a flourishing of new life."