The extinction of a large number of species within a relatively short period of geological time, thought to be due to factors such as a catastrophic global event or widespread environmental change that occurs too rapidly for most species to adapt. At least five mass extinctions have been identified in the fossil record, coming at or toward the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous Periods. The Permian extinction, which took place 245 million years ago, is the largest known mass extinction in the Earth's history, resulting in the extinction of an estimated 90 percent of marine species. In the Cretaceous extinction, 65 million years ago, an estimated 75 percent of species, including the dinosaurs, became extinct, possibly as the result of an asteroid colliding with the Earth. Compare background extinction.
IT’S A WORD OF THE DAY QUIZ BONANZA!
This windfall of words will make you rich with knowledge. Mine your memory on the words from July 27 to August 2!
Question 1 of 7
What does "scattergood" mean?
a person who acts as though he or she knows everything and who dismisses the opinions, comments, or suggestions of others.
a person who spends possessions or money extravagantly or wastefully; spendthrift.
a well-intentioned but naive and often ineffectual social or political reformer.TAKE THE QUIZ TO FIND OUT
Words nearby mass extinction
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Cultural definitions for mass extinction
notes for mass extinction
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.