Impacts and their role in Extinction
Bad Joke
People have known about enormous craters, such as the famous
Meteor Crater,
in N. Arizona, for some time. Over 200 are known
on the surface of the Earth, and that does not include those
which must exist on the ocean floor. There are few really big
ones (100 km or more in diameter) and they are 10s to 100s of million
years old. What size object could cause such a crater and
what effect would such collisions have on life at that time?
Extinction of the Dinasours.
At the K-T (Cretaceous / Tertiary) Boundary 65 million years ago, a substantial fraction of life on earth (40%),
including the Dinasours, died out suddenly. When examining the
layers of rock from this time, geologists found
the iridium abundance 10 times
that seen in 'terrestrial' rocks. Dense quartz, typical of impact sites,
was also found. For a tour of the Iridium Hill region (seen left),
showing the K-T boundary,
go HERE.
Where was the crater to substantiate an extraterrestrial
cause for the extinction 65 million years ago? What if it
landed in the ocean? Based on the iridium abundance,
the impact object was predicted to be 10 km and
to have created a crater 100 km wide.
Chicxulub Crater in the Yucatan
Lying half on land, half in water, this 200 km crater was formed
by an object about 10-20 km in size.
This crater was found in 1980 only after specifically searching
for the K-T crater. It lies under 1 km of debris. More on
the crater HERE.