Running head: MASS EXTINCTION
History of Life - Mass Extinction
Susan Penick
Western Governor’s University
QXT2 ID Biological Science
March 13, 2015
History of Life - Mass Extinction
More than 99 percent of all species that have ever lived are now extinct. Usually, extinctions happen gradually, but several times in Earth’s history mass extinctions wiped out entire ecosystems. During these events, some biologists propose, “many species became extinct because their environment was collapsing…
Words 784 - Pages 4