Science, Tech, Math › Animals & Nature The Triassic-Jurassic Mass Extinction Share Flipboard Email Print DEA PICTURE LIBRARY/Getty Images Animals & Nature Evolution History Of Life On Earth Human Evolution Natural Selection Evolution Scientists The Evidence For Evolution Resources Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Dinosaurs View More By Heather Scoville Science Expert M.A., Technological Teaching and Learning, Ashford University B.A., Biochemistry and Molecular Biology, Cornell University Heather Scoville is a former medical researcher and current high school science teacher who writes science curriculum for online science courses. our editorial process Heather Scoville Updated July 17, 2019 Over the entire 4.6 billion year history of the Earth, there have been five major mass extinction events. These catastrophic events completely wiped out large percentages of all of the life around at the time of the mass extinction event. These mass extinction events shaped how the living things that did survive evolve and new species appear. Some scientists also believe we are currently in the middle of the sixth mass extinction event that could last for a million years or more. The Fourth Major Extinction The fourth major mass extinction event happened around 200 million years ago at the end of the Triassic Period of the Mesozoic Era to usher in the Jurassic Period. This mass extinction event was actually a combination of smaller mass extinction periods that happened over the final 18 million years or so of the Triassic Period. Over the course of this extinction event, it is estimated more than half of the known living species at the time completely died out. This allowed dinosaurs to thrive and take over some of the niches left open due to the extinction of species that had previously held those types of roles in the ecosystem. What Ended the Triassic Period? There are several different hypotheses on what caused this particular mass extinction at the end of the Triassic Period. Since the third major mass extinction actually is thought to have occurred in several small waves of extinctions, it is entirely possible that all of these hypotheses, along with others that may not be as popular or thought of as of yet, could have caused the overall mass extinction event. There is evidence for all of the causes proposed. Volcanic Activity: One possible explanation for this catastrophic mass extinction event is unusually high levels of volcanic activity. It is known that large numbers of flood basalts around the Central America region occurred around the time of the Triassic-Jurassic mass extinction event. These enormous volcano eruptions are thought to have expelled huge amounts of greenhouse gases like sulfur dioxide or carbon dioxide that would quickly and devastatingly increase the global climate. Other scientists believe it would have aerosols expelled from these volcanic eruptions that would actually do the opposite of the greenhouse gases and end up cooling the climate significantly. Climate Change: Other scientists believe it was more of a gradual climate change issue that spanned the majority of the 18 million year time span attributed to the end of the Triassic mass extinction. This would have led to changing sea levels and even possibly a change in the acidity within the oceans that would have affected species living there. Meteor Impact: A less likely cause of the Triassic-Jurassic mass extinction event may be attributed to asteroid or meteor impact, much like what is thought to have caused the Cretaceous-Tertiary mass extinction (also known as the K-T Mass Extinction) when the dinosaurs all went extinct. However, this is not a very likely reason for the third mass extinction event because there has been no crater found that would indicate it could create devastation of this magnitude. There was a meteor strike that dates to about this time period, but it was rather small and is not thought to have been able to cause a mass extinction event that is thought to have wiped out more than half of all living species on both land and in the oceans. However, the asteroid impact may have very well caused a local mass extinction that is now attributed to the overall major mass extinction that ended the Triassic Period and ushered in the beginning of the Jurassic Period.