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Anther occurred when the Cretaceous period became the Tertiary about 65 million years ago, when 75 percent of species disappeared. This article is about the first mass extinction at the end of the Ordovician geological period 440 million years ago, when about 86 percent of species were killed.
Many species vanished in five cataclysmic mass extinctions and today, 99.9 percent of all species that have existed on Earth are extinct. T he Ordovician-Silurian extinction occurred about 439 million years ago due to a drop in sea levels as glaciers formed followed by rising sea levels as glaciers melted.During this extinction 25 percent of marine families and 60 percent of marine genera (the classification above species) were lost.T he Late Devonian extinction took place somewhere around 364 million years ago. To this day its cause is unknown.uring this extinction 25 percent of marine families and 60 percent of marine genera (the classification above species) were lost. T he Late Devonian extinction took place somewhere around 364 million years ago.