Syllabus Edition
First teaching 2015
Last exams 2025
What Caused Mass Extinctions on Earth? (DP IB Environmental Systems & Societies (ESS))
Revision Note
Mass Extinctions
Mass extinctions of the past have been caused by various factors, such as:
Tectonic plate movements
Super-volcanic eruption
Climatic changes (including drought and ice ages)
Meteorite impact
All of these have resulted in new directions in evolution and therefore led to increased biodiversity
How many mass extinctions have there been?
Name | Time Period | Causes | Results for Biodiversity |
|---|---|---|---|
Ordovician-Silurian | 443-485 million yrs ago | A series of glaciations caused a global cooling event which led to a sea-level fall and the contraction of shallow water habitats. This, in turn, caused the widespread extinction of marine life. Additionally, the cooling of the ocean led to a reduction in oxygen levels, which caused widespread oceanic anoxia. | 85% of marine species were lost, including many brachiopods, bryozoans, and trilobites. The extinction of brachiopods paved the way for the evolution of the bivalves in the succeeding periods. |
Late Devonian | 364-375 million yrs ago | Climate change caused by the spread of land plants reduced the amount of CO2 in the atmosphere. This, in turn, led to global cooling and a decline in sea levels, which caused widespread marine extinction. | 70% of marine species were lost, including many brachiopods, corals, and trilobites. |
Permian-Triassic | 251 million yrs ago | Massive volcanic activity in Siberia, covering an area equivalent to the size of Western Europe, released huge amounts of greenhouse gases and other toxins into the atmosphere and ocean, causing global warming, oceanic anoxia, and ocean acidification. | 96% of marine species were lost, including almost all trilobites and corals. 70% of terrestrial vertebrate species were also lost, including many reptiles and amphibians. The event marked the end of the Paleozoic Era and the beginning of the Mesozoic Era. |
Triassic-Jurassic | 199-214 million yrs ago | Climate change caused by massive volcanic activity led to global warming and a decline in sea levels, which caused widespread marine extinction. The resulting loss of habitat, along with the changes in temperature and precipitation, also led to the extinction of many terrestrial species. | 50% of marine species were lost, including many corals, molluscs, and ammonites. Many terrestrial species were also lost, including many crocodile-like reptiles, mammal-like reptiles, and early dinosaurs. The extinction paved the way for the diversification of the dinosaurs in the succeeding periods. |
Cretaceous-Paleogene | 65 million yrs ago | An asteroid impact in the Yucatan Peninsula, combined with massive volcanic activity in India, caused global cooling, acid rain, and widespread wildfires. The impact also caused a global tsunami and triggered earthquakes, which caused widespread destruction. The resulting loss of habitat and changes in temperature and precipitation contributed to the extinction. | 75% of all species were lost, including all non-avian dinosaurs, pterosaurs, and ammonites. |
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