Geoscientists in Scotland say they have evidence to disprove the
controversial "Snowball Earth" theory - the idea that the planet was
completely encased in ice just over 600 million years ago.
The team, from the University of St Andrews, has published its
findings in the scientific journal Geology, after studying rocks in
the west of Scotland, Ireland, Namibia and California.
Drs Dan Condon, Tony Prave and Doug Benn say they have found
evidence of sedimentary material, which could only have been derived
from floating ice on open oceanic waters.
This, they believe, indicates that the Earth's oceans could not
have been frozen during the snowball years.
The controversial theory that for millions of years the Earth
was entirely smothered in ice, up to one kilometre thick, has been
kicked around for more than 50 years.
It rests on the apparently anomalous evidence of past glaciation
in places that should have been much too hot - very near the
equator. Even during the most severe ice age, many scientists
thought that the ice only reached as far down as Northern Europe and
the middle of the USA.
"Snowball Earth" supporters claim that the supposed freeze would
have caused severe environmental stresses upon early life.
This would have resulted in repeated mass extinctions followed
by an "explosion" of more complex (multi-cellular) lifeforms on
Earth once the thaw came.
But Drs Condon, Prave and Benn say their work casts severe doubt
on the Snowball Earth idea.
The team examined a suite of rocks called Port Askaig Tillite,
south west of Oban in Scotland and directly north of Jura, which is
supposed to record Snowball Earth glaciations.