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.