Chicxulub

It is generally accepted now that a 10-kilometer diameter comet or asteroid slammed into the Earth 65 million years ago and caused the extinction of around 50% of the species on the planet at the time.

The extinction was caused by tidal waves and fires, but mostly by climatic changes that occurred following the impact:

  • The chemistry of the atmosphere likely changed through having an enormous amount of unusual elements in it. The most likely result was global acid rain which killed much of the plant life.

  • The amount of sunlight that reached the Earth probably diminished substantially from the cloud of dust that was thrown into the atmosphere.

    Both the acid rain and the dust cloud probably stayed in the atmosphere for years (or more?). The result is that many photosynthesizing organisms which are low on the food chain died out, and the effects rippled all the way to the top of the food chain.

    All of these conditions altered the climate of the time and stressed the plants and animals, and many of them did not survive. Remember from our evolution discussion though that a stressed condition often produces dramatic evolutionary changes. New organisms were able to succeed in the aftermath of the impact and its global effects. Some of those new organisms were the mammals.

    http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Regional_Effects.html

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