User blog comment:JMAC308/Mark of athena/@comment-4551739-20111104035919/@comment-4531192-20111106184221

You're right again. However in Wikipedia it says that "In the past 540 million years there have been five generally-accepted, major mass extinctions that on average extinguished half of all species. One of the largest mass extinction to have affected life on Earth was in the Permian-Triassic ... [that] killed off 90% of all species." So the probability of such event taking place is minimalistic, and even if it happened the humans would stand a chance of recovering from it (though it would probably take thousands of years).