250 million years ago, this planet suffered the greatest mass extinction of multicellular life in the long history of the planet. The ocean conveyor current stopped. The ocean became anoxic, meaning it had little or no oxygen. Fish died; sulfur producing bacteria thrived. As the anoxic layer of the ocean reached the surface, hydrogen sulfide gas was released into the atmosphere in toxic quantities. The sky turned green. The mass extinction was brought onto land.
95% of all species on the planet died. This was due to global warming.*