Extinction is the process by which a group of taxa or species dies out, reducing biodiversity.[237] The moment of extinction is generally considered the death of the last individual of that species. Because a species’ potential range may be very large, determining this moment is difficult, and is usually done retrospectively after a period of apparent absence. Species become extinct when they are no longer able to survive in changing habitat or against superior competition. In Earth’s history, over 99% of all the species that have ever lived are extinct;[238][129][130][131] however, mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify