66 million years ago, at the end of the Cretaceous, a giant meteor hit the Earth, in the Yucatan in Mexico, the Shiva crater, offshore India, Silverpit crater in the North Sea, and the Boltysh crater in Ukraine, that caused a mass extinction of species. We have evidence of the craters, but also going on at this time, was the massive basalt volcanism in India. The climate changed and many species died out.
There was also and much earlier mass extinction 250 million years ago, but until now no crater had been found. There has been plenty of plate movements, volcanism, and time to remove the evidence.
But Eric Tohver thinks he may have discovered the crater and the mechanism. In Brazil there is a small crater, originally only 25 km across, compared to the Yucatan crater which is 180 km across. Seemingly too small to have a dramatic effect on the climate of Earth, but exactly in strata of the right age.
Eric Tohver has discover the rock that the meteor impacted was rich in hydrocarbons, and the impact was sufficient to release a huge volume of oil and gas, mostly methane, a very efficient greenhouse gas. This was the Permian Extinction. 90% of marine species died and 70% of land species.
The 2012 Chelyabinsk meteor over Russia was just a little one.