BIOC50H3 Lecture Notes - Lecture 11: Macroevolution, Ordovician, Cenozoic
22 Dec 2018
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Document Summary
It"s estimated that perhaps 98% of species that have ever evolved have gone extinct. Currently there are estimated to be between 7 and 100 million species on our planet if no species have ever gone extinct, we would have currently have 323 million to 4. 9 billion species on the planet! Therefore, in order for biodiversity to stay the same, speciation rate = extinction rate. Looking at mass extinction events: species naturally arise and go extinct. Graph: plots number of marine genera through time: green: genera with detailed fossil records, grey: genera with less detailed fossil records. There is a general trend in both: there is an increase in species diversity from about 200. Mya to the present this suggests that speciation rates are bigger than extinction rates at about times. When extinction rates greatly exceed speciation rates, we get a mass decline in biodiversity indicates a mass extinction event. There are the big five mass extinctions and other minor ones.
