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Palaeozoic World

Wilkes Land Permian Impact Crater

Edited from BBC News, 3 June 2006. Updated 18 December 2017

What appears to be a 480 kilometre-wide crater (300 miles) was detected under the East Antarctic Ice Sheet during a survey which concluded in 2006. The scientists behind the discovery said it could have been made by a massive meteorite strike 250 million years ago.

At that time, Antarctica formed part of the Pangean supercontinent (the name Pangea is Greek, meaning 'all earth', to describe the single, massive continent).

Pangea was the most recent of perhaps three supercontinents to have formed over the last billion years, beginning to break apart from around 175 million years ago into the continents seen today which eventually will drift so far apart that they reform on the other side of the planet to create a new supercontinent.

The feature at Wilkes Land was found by Nasa satellites which were mapping subtle differences in Earth's gravity. This Wilkes Land impact was much bigger than the impact that killed the dinosaurs, according to Professor Ralph von Frese, from Ohio State University, in the US.

If the crater really was formed at the time von Frese and colleagues believed, it would raise interest as a possible cause of the 'great dying' - the biggest of all of Earth's mass extinctions when ninety-five percent of all marine life and seventy percent of all land species disappeared. It was out of this extinction event that the first of the dinosaurs emerged to become dominant predator.

Some scientists have long suspected that the extinction at the boundary of the Permian and Triassic (PT) Periods could have occurred quite abruptly - the result of environmental changes brought on by the impact of a giant space rock.

It is a similar argument to the one put forward to explain the demise of the dinosaurs at the much later date of 65 million years ago, although that argument has a more firm footing after the impact crater in the Gulf of Mexico was identified.

A geological structure, known as the Bedout High, in the seabed off the northern coastal border of what is now Western Australia, has also been suggested as the possible crater remains from the PT impactor.

But the impact explanation for the great dying is an argument that has struggled to find favour.

The prevailing theory is that several factors - including supervolcanism (where magma rises from the earth's mantle and accumulates in the crust. The heat of the liquid rocks causes more of the solid crust to melt, forming a magma chamber which often causes the pressure to rise more and more and can lead to eruptions on such a massive scale that an ice age can be triggered as a result), and extensive climate warming - combined over thousands of years to strangle the planet's biodiversity.

Earth may well have been hit by extraterrestrial objects, but it is unlikely there was some killer punch from space, these other researchers contend. This prevailing, longer-term theory is covered in more detail in the accompanying feature, Molluscs Ruled the World before Dinosaurs (see sidebar links, right).

The Ohio-led team used gravity fluctuations measured by the US space agency's Grace satellites to peer beneath Antarctica's icy surface. Team members were drawn from the US, Russia, and Korea.

The crater information was first presented at the recent American Geophysical Union Joint Assembly in Baltimore.

Pangean supercontinent
Permo-Triassic extinction around the Pangean supercontinent
  • The greatest of all Earth's mass extinctions occurred about 250 million years ago
  • About 95% of marine species and three-quarters of all families on the Pangean landmass (above) perished
  • Rocks from the end of the Permian period can be seen today in places such as China, Italy and Pakistan
  • Chief suspects include sea-level fluctuations, volcanic activity, space impacts and melting methane-ice in sea sediments
 

 

     
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