The Five Worst Extinctions in Earth's History Thurs. Here are details of the five worst mass extinctions in Earth s history and their possible causes, according to paleobiologist Doug Erwin of the Smithsonian Institution s National Museum of Natural History. Some argue for other causes, including gradual climate change or flood-like volcanic eruptions of basalt lava from India s Deccan Traps. The volcanism may have led to deadly global warming. Rocks from the eruptions now are found in the eastern United States, eastern Brazil, North Africa and Spain.
Vertebrate deaths are unclear.
Permian-Triassic extinction , about 251 million years ago. Many scientists suspect a comet or asteroid impact, although direct evidence has not been found. Others believe the cause was flood volcanism from the Siberian Traps and related loss of oxygen in the seas. Still others believe the impact triggered the volcanism and also may have done so during the Cretaceous-Tertiary extinction. Late Devonian extinction , about 364 million years ago, cause unknown.