The last and probably most well-known of the mass-extinction events happened during the Cretaceous period, when an estimated 76% of all species went extinct, including the non-avian dinosaurs. This was possibly caused by some colossal geological activity in what is today the Atlantic Ocean that would have elevated atmospheric CO₂ concentrations, increased global temperatures, and acidified oceans. Some other possible causes are still debated, such as massive volcanic activity in what is today Siberia, increasing ocean toxicity caused by an increase in atmospheric CO₂, or the spread of oxygen-poor water in the deep ocean.įifty million years after the great Permian extinction, about 80% of the world’s species again went extinct during the Triassic event. These could have blocked the sun and generated intense acid rains. Some of the suggested causes include an asteroid impact that filled the air with pulverised particle, creating unfavourable climate conditions for many species. This wiped out more than 95% of all species in existence at the time. from The third and most devastating of the Big Five occurred at the end of the Permian period around 250 million years ago. To establish a ‘mass extinction’, we first need to know what a normal rate of species loss is.
It was also the time when plants were starting to take over dry land, and there was a drop in global CO 2 concentration all this was accompanied by soil transformation and periods of low oxygen. This period in Earth’s past was characterised by high variation in sea levels, and rapidly alternating conditions of global cooling and warming. This affected around 75% of all species, most of which were bottom-dwelling invertebrates in tropical seas at that time. The second mass extinction occurred during the Late Devonian period around 374 million years ago. First, a planetary-scale period of glaciation (a global-scale “ice age”), then a rapid warming period. The Ordovician event seems to have been the result of two climate phenomena. The first mass extinction happened at the end of the Ordovician period about 443 million years ago and wiped out over 85% of all species. Each event itself lasted between 50 thousand and 2.76 million years. These five mass extinctions have happened on average every 100 million years or so since the Cambrian, although there is no detectable pattern in their particular timing. Corey Bradshaw, Author provided The Big Five The fossil record can help us estimate prehistoric extinction rates. An ammonite fossil found on the Jurassic Coast in Devon.
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