[ASC-media] media release: Asteroid impact, snowball Earth and Ediacarans

Heather Catchpole catchpoleheather at gmail.com
Tue Oct 19 03:44:20 CEST 2010


*Media release Australian Journal of Earth Sciences*

*Asteroid impact, snowball Earth and Ediacarans***

Extreme cold and a giant asteroid impact in South Australia may have
influenced the evolution of the Ediacarans, some of the earliest complex
life on Earth, says new Australian research.

The Ediacarans are a weird bunch of organisms that included the world’s
first large-scale complex life. During the time they lived (the Ediacaran
Period, 635–542 million years ago); the Earth experienced at least one cold
snap that may have covered much of the Earth in ice (the controversial
‘snowball Earth’ hypothesis). At that time, southern Australia lay near the
equator and low latitudes were devastated by the impact of a
~4.7-kilometre-diameter asteroid that left a 90-km crater in central South

Now, a paper to published in the current edition of the *Australian Journal
of Earth Sciences *(*www.ajes.com.au*)* *by Australian geologists shows that
this massive impact – which struck with an estimated energy of 5.2 million
megatons of TNT – coincided with a period of glaciation.

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

“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,” write Associate
Professor Victor Gostin and colleagues David McKirdy, Lynn Webster and
George Williams, all from the University of Adelaide, in their paper
‘Ediacaran ice-rafting and coeval asteroid impact, South Australia: Insights
into the terminal Proterozoic environment’ (AJES 57/7, 2010).

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 the
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, the team says.

“The Acraman impact took place at a low paleolatitude (~12.5°) and would
have strongly affected the mid-Ediacaran environment and adversely affected
the global environment,” says Gostin.

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

In a commentary on the paper to be published in the Geological Society of
Australia’s *The Australian Geologist* magazine, Professor Malcolm Walter,
Director of the Australian Centre for Astrobiology at the University of New
South Wales, says the evidence from Gostin *et al* resolves issues around
the timing and record of the glaciation, the impact and the rise of the
Ediacaran biota.

“What [they] are proposing is an asteroid impact during a time of frigid
climate, a double whammy to the biosphere,” says Walter, who was not
involved in the research.

Rather than an extinction event, what seems to follow the Acraman impact was
a “flourishing of exotic plankton and the first macroscopic animals”, Walter
continues, similar to the flourishing of mammals after the dinosaurs were
wiped out by a huge impact 65 million years ago.

“Did the Acraman impact and coincidentally coeval glaciation help trigger
one of the great biological revolutions in Earth history? Time will tell,”
says Walter.

Link to paper:


Ass Prof Victor Gostin

Honorary Visiting Research Fellow, University of Adelaide

*0423 14 3300/ *08 8303 4039

victor*.*gostin at adelaide*.*edu*.*au <victor.gostin at adelaide.edu.au>

Professor Malcolm Walter

Director, Australian centre for Astrobiology

University of New South Wales

*0428 111 251*/ 02 9385 3761

malcolm.walter at unsw.edu.au

Heather Catchpole

Assistant Editor, *Australian Journal of Earth Sciences*

0401068975/ 02 98091539

catchpoleheather at gmail.com

Heather Catchpole

Freelance science content
Deputy Editor, The Australian Geologist/ Assistant Editor, The Australian
Journal of Earth Science
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