More links: http://news.bbc.co.uk/1/hi/sci/tech/3520837.stm
The case of the missing dinosaurs is certainly getting curiouser and curiouser. Scientists now seem to have second thoughts on the long-held theory that a single, massive asteroid hit wiped out the dinosaurs some 65 million years ago. The Chicxulub crater off the Mexican peninsula — considered as the smoking gun for the catastrophe — has thrown up new evidence to suggest that the actual collision predated the departure of the dinos by some 300,000 years.
Researchers studied rock samples from the Chicxulub structure using indicators of age like fossil planktonic organisms and reversal patterns in the earth’s magnetic field to turn the original theory on its head. At several spots on Earth, a clay layer separates rocks laid down in the Cretaceous period from those deposited in the Tertiary: the so-called K-T boundary which marks the point when the great beasts died out. The impact transformed the earth’s climate and made it impossible for the dinos to exist so that mammals could take advantage and thrive, think, and, yes, editorialise on the episode.
The latest study, however, indicates that the dinos, already reeling
from the effects of the first asteroid impact, were about to sign
off at the K-T boundary when the second space rock did them in. Curiously,
this theory may receive a leg-up from another popular assumption
that volcanism in India bled the great beasts to death. A vast ‘flood’ of
lava and gas in India at about the same time could have played a
decisive role in poisoning the planet’s biosphere. This seems
to tie in neatly with the latest finding. But the problem with these
theories is that it’s so difficult to test them. For thanks
to the constant churning of the earth’s tectonic processes,
few rocks from the late Triassic are still around.