Dinosaur
doomsday was wetter than scientists have thought, according to new images of
the crater where the space rock that likely killed the jumbo reptiles landed.
Sixty-five
million years ago the asteroid struck the coast of the Yucatan Peninsula, and
most scientists think this event played a large role in causing the extinction
of 70 percent of life on Earth, including non-avian dinosaurs.
Geophysicists
now have created the most detailed 3-D seismic images yet of the mostly
submerged Chicxulub
impact crater. The data reveal that the asteroid landed in deeper water
than previously assumed and therefore released about 6.5 times more water vapor
into the atmosphere.
The
images also show the crater
contained sulfur-rich sediments that would have reacted with the water vapor to
create sulfate aerosols. These compounds in the atmosphere would have made the
impact deadlier by cooling the climate and producing acid rain.
"The
greater amount of water vapor and consequent potential increase in sulfate
aerosols needs to be taken into account for models of extinction
mechanisms," said Sean Gulick, a geophysicist at the University of Texas at Austin who led the study.
The
findings will be published in the February 2008 issue of the journal Nature
Geosciences.
The
asteroid impact alone was probably not responsible for the mass extinction,
Gulick said. More likely, a combination of environmental changes over different
time scales took their toll.
Many
large land animals, including the dinosaurs, might have baked to death within
hours or days of the impact as ejected material fell from the sky, heating
the atmosphere and setting off firestorms. More gradual changes in climate and
acidity might have had a larger impact in the oceans.
If
there was more acid rain than scientists had previously calculated, that could
help explain why many smaller marine creatures were affected, because the rain
could have turned the oceans more acidic.
There
is some evidence that marine organisms more resistant to a range of pH survived,
while more sensitive creatures did not.
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