Some people have now started to look for iridium spikes in the rock record at the locations of other mass extinctions.

Recall the impact probability plot: a 10-km body should impact the Earth every 100 million years.

Remember, mass extinctions have occured every maybe every 26 million years, with large extinctions happening five times in the past 500 million years.

http://www.carleton.ca/~tpatters/teaching/intro/extinction/extinction1.html

So far, there has been a little evidence that suggests that perhaps one or several other of the mass extinctions in the last 500 million years could have been caused by an impact, but no proof as good as the Cretaceous-Tertiary boundary event.

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