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http://www.newsweek.com/five-mass-extinctions-earth-history-630314

13 AM Close Opinion mass extinctionThis article was originally published on The Conversation. Read the original article.Of all the species that have ever lived, more than 99 percentare now extinct. Most of them quietly disappeared during periods of background extinction,whereby a handful of species become extinct every 100,000 years or so.But there were also occasions when extinction rates increased rapidly in short periods of time and wiped out a significant proportion of all life on Earth. These are known as mass extinctions. They have profoundly influenced the history of lifeand many scientists now argue that we are in the midst...