Paleobiologists generally recognize the five most severe mass extinctions during the Phanerozoic Eon. Along with the other students in this class, determine when each of these “Big Five” mass extinctions occurred. Include in the discussion a brief list of which organisms went extinct during each of these events and which organisms radiated afterwards. You should use the information from this unit and from Internet searches to help you in this discussion. NO plagiarism will be permitted.

Extinction of the Ordovician: This extinction was responsible for the disappearance of about 60-70% of the species of oceanic life, This is because in that period most of the life on Earth was in the ocean. This extinction is believed to have been caused by an intense glacial period, although short that froze most of the planet's water. It is believed that the species most affected were sponges, algae, jawless fish, molluscs and cephalopods.

Devonian Extinction: Responsible for the disappearance of about 75% of marine species. This extinction was caused by the depletion of oxygen in the ocean, making life impossible for all aerobic marine organisms. This depletion of oxygen was caused mainly by the variation in the level of the ocean and climatic changes that may have been caused by asteroids.

Permian Extinction: Responsible for the death of 95% of life on earth. This extinction is known as the "mother of all extinctions" due to its destructive character, which devastated life on land and in the ocean. It is believed that this extinction was caused by volcanic activities triggered by the impact of asteroids. Almost all living species on earth were affected, such as insects, trilobites, sharks, boneless fish, reptiles, among others.

Extinction of the Triassic: It is not known exactly what caused this extinction, but it is estimated that it had the power to decimate 70-80% of terrestrial life, mainly arcosaurs and amphibians. The most accepted theory today is that the extinction was caused by recurrent volcanic activities that influenced huge volumes of carbon dioxide in the atmosphere, generating intense heating.

Cretaceous extinction: It was caused by the impact of an asteroid with the earth. The impact had the power to exterminate 75% of terrestrial life. This is the most well-known extinction, since it was responsible for decimating dinosaurs, however, some animals survived this impact, such as most marine species, frogs, birds, reptile and mammals.

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