Impacts and their role in Extinction
Bad JokePeople 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. Most of the really big ones (100 km or more in diameter) are usually over a billion 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, 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.
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 200-300 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.
Objects up to about 1 km in diameter will cause extreme
local damage, but pose no global threat. However objects
greater than 1 km in diameter, resulting in 1 million megatons
of TNT, would be large enough to perturb the
Earth's climate on a global scale. About 25% of humanity
would be wiped out. How often do such events occur?
Every several ten million years.
Every 100 years, something 50 meters in size strikes Earth. Such an object, like that which hit Tunguska in 1908, has 1000x the energy of the bomb that fell on Hiroshima. It would destroy an area the size of Rhode Island.