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Cretaceous Extinction
About
65 million years ago, SOMETHING big happened on planet Earth
resulting in the mass extinction of 3/4 of all living species
- not just dinosaurs, but plants and marine life, too. Evidence
uncovered all over the world strongly suggests that a meteor
the size of Manhattan slammed into the planet, setting in
motion a cascade of events culminating in the great die-off.
In the late 1970's, father and son geologists Luis and Walter
Alvarez discovered a unique layer of clay dating back to this
period of major upheaval in Gubbio, Italy. Analysis of this
layer - known by geologist as the K-T boundary layer - revealed
that it contained a surprising amount of the element Iridium,
the presence of which in the Earth's crust signifies two possible
events. Iridium may be brought up via volcanic eruption from
deep within the Earth's core, or it can arrive here aboard
a meteor.
While
a catastrophic volcanic eruption could also account for the
extinction, other evidence favors the meteor hypothesis. Scientists
already had calculated that a meteor some six miles across
could explain the amounts of Iridium in the K-T layer, when
geophysicist Alan Hildebrand found evidence of an ancient
impact crater on Mexico's Yucatan Peninsula. The 125-mile-wide
ring sits under 3000 feet of rock, and, dramatically, dates
back to 65 million years ago.
Scientists
calculate that the impact would have exploded with 10,000
times the force of the world's total nuclear weapons arsenal.
The cataclysm caused a shock wave that physically altered
the rocks around the site, started a global wildfire, triggered
a tsunami tidal wave, caused earthquakes and prompted volcanic
eruptions. Together, all these events meant the entire planet
was likely covered in darkness for months and veiled in haze
for years. Global temperatures must have dipped to freezing
and the entire food chain probably collapsed.
It's
not the first time - nor probably the last time - a meteor
impact shook things up on planet Earth. But it was more than
likely this impact 65 million years ago that put an end to
the dinosaurs and gave smaller, warm-blooded mammals their
chance to find a niche in the world.
For
more information, see:
Dinosaur Extinction Page
http://web.ukonline.co.uk/a.buckley/dino.htm
How
Dinosaurs Became Extinct
http://www.auburn.edu/~kindat/chap2.htm
Click
on a thumbnail picture to learn about another
great moment in global climate change:
      
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