Asteroid influenced evolution of Ediacarans: Study

The evolution of Ediacarans could have been influenced by extreme cold and a giant asteroid impact.

Melbourne: The evolution of Ediacarans, some of the earliest complex life on Earth, could have been influenced by extreme cold and a giant asteroid impact which caused massive environmental stresses, says a new study.

The Ediacarans are a weird bunch of organisms that included the world`s first large-scale complex life. During the time they lived (635-542 million years ago) in southern
Australia, the Earth experienced at least one cold snap that may have covered much of the Earth in ice.

At that time, southern Australia lay near Equator and low latitudes were devastated by impact of a 4.7-km-diameter asteroid that left a 90-km crater in central South Australia.

Now, a team of Australian geologists shows that this massive impact -- which struck with an estimated energy of 5.2 million megatons of TNT - coincided with period of glaciation, the `Australian Journal of Earth Sciences` reported.

The effect of this double whammy -- extreme cold and killer asteroid -- could have been a major factor influencing the evolution of the Ediacarans, say the geologists.

"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," said team leader Victor Gostin of University of Adelaide.

The impact site is at Lake Acraman in the Gawler Ranges, and ejecta of shattered rocks flung out by the impact is found in mudstones about 580 million years old at several places in South Australia, including the Flinders Ranges and north-western South Australia, 250 to 550 km from impact site.

Coinciding with this ejecta is glacial debris as pebbles and gritty sediments left by floating ice. The observations suggest that the Acraman impact occurred during, but did not trigger, a cold interval marked by sea ice and glacial ice, according to the geologists.

"The Acraman impact took place at a low paleolatitude (12.5 degrees) and would have strongly affected mid-Ediacaran environment and adversely affected the global environment," said Gostin.

The Ediacarans, which first appeared several million years after the impact and whose type locality is in the South Australian Flinders Ranges, include range of unique organisms that resemble jellyfish, sponges, marine worms, but unrelated and bizarre forms whose lifestyle remains a mystery.