Originally Posted by Amphitrite
Funnily enough I had an interesting conversation about this with somebody last night.
If an asteroid were to pass close enough to the earth - apparently it could have devastating effects such as tidal waves. I don't really know much about it, but apparently asteroids have been the biggest cause for extinction of species on earth.
Second most, Amphitrite :) 250 Million years ago a massive upwelling of methane from the sea bed followed by catastrophic volcanic activity wiped out 99 percent of all life on Earth. The most successful marine creature of the time, trilobites, who numbered in the thousands of species, ceased to exist. It's like a knife cut in strata of that time; before, life, after, none.
The asteroid that doomed the dinosaurs 65 million years ago drove only 75 to 80 percent of animals to extinction, ushering in the age of mammals. Not terribly long ago they found the crater from that asteroid, etched into the sea floor bedrock near the Yucatan Peninsula.
If neither of those extinction level events had happened, who knows what the world would be like today. Perhaps the only creatures still with us from the asteroid 65 million years ago are the crocodilians, who haven't changed very much at all in the last 150 million years. Nature obviously got them right :)