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Ice, an Asteroid Impact and the Rise of Complex Life


An iceberg carrying rock debris into the Antarctic Ocean near Casey Station. Photo: David Wakil

By Victor Gostin, David McKirdy and George Williams

An asteroid impact in southern Australia is redefining the conditions that preceded the explosion of multicellular life more than 500 million years ago.

Victor Gostin, David McKirdy and George Williams are with the School of Earth & Environmental Sciences at the University of Adelaide.

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Some of the major events during the Earth’s history have occurred simultaneously or in close succession. The consequences of these events have led scientists to conclude that the synchronicity of these global disasters has been a powerful driver of ecological and evolutionary change.

For example, the impact of a huge asteroid measuring ~12 km in diameter at the end of the Cretaceous Period 65 million years ago was the death-knell for the dinosaurs. The impact on Mexico’s Yucatan Peninsula coincided with extremely large and extensive basaltic eruptions in India known as the Deccan Traps. The combined effect of these two events on the Earth’s atmosphere and oceans evidently spelt the end not only of the dinosaurs but also of the marine ammonites and most other creatures in the upper few metres of all oceans and inland waters. This set the scene for the subsequent explosion of mammalian evolution.

Several geological eras earlier, before the dawn of multicellular animal life, a smaller but significant asteroid measuring ~4.7 km in diameter hit South Australia around 580 million years ago at Lake Acraman in the Gawler Ranges. The impact site in ancient volcanic rocks now bears the deeply eroded scar of the initial transient cavity, measuring ~40 km in diameter, that led to the formation of a larger collapsed crater ~90 km across.

Because of its equatorial...

The full text of this article can be purchased from Informit.