The gigantic lava flow in Siberia lasted upward of a million years and flooded an area about the size of the lower 48 United States with layer upon layer of dark basalt lava — thousands of feet thick.

Some geologists suspect the eruption was caused by an extra-large plume of hot material welling up from the edge of the Earth's core. But what makes it especially important is that the Siberian Traps is the prime suspect in wiping out 90 percent of all living species 251 million years ago — the most severe extinction event in Earth's history.

"This is the numero uno candidate for a mass extinction caused by volcanism," said paleontologist Spencer Lucas, a curator at the New Mexico Museum of Natural History. "There's good reason to believe it had something to do with that extinction."

Not all scientists agree that the Siberian Traps were the main reason for the mass extinctions. But the timing of the Siberian eruption is perfect, for those looking for a culprit: It crosses a boundary in geologic time that marks the great die-off at the end of the Permian period and the beginning of the Triassic period (the P-T extinction).

And unlike the more famous dinosaur-killing Cretaceous-Tertiary mass extinction (aka the K-T extinction) 65 million years ago, the Permo-Triassic extinctions have not been linked to giant asteroids.

Since the Siberian flood basalts, as they are called, poured out during the time of the mass extinction, it's reasonable to think they might have played a role, said paleontologist Gerta Keller of Princeton University.

There are recent examples, after all, of the global impact of even relatively minor volcanic eruptions. The 1991 eruption of Mount Pinatubo in the Philippines, for example, sent millions of tons of sulfur dioxide into the atmosphere. One of the largest volcanic eruptions of the 20th century, it caused a recordable drop in global temperatures (a few tenths of a degree) for several years. And it was at least thousands of times smaller than the Siberian Traps eruption.

There is even reason to believe that an eruption of the largest super volcano in the recent history of the Earth — the Toba caldera on Sumatra, Indonesia — caused enough climate change to almost wipe out humanity 74,000 years ago.

As for exactly how the Siberian eruption could wipe out most life worldwide, it's probably not simply by burying the Earth in lava or ash, says Lucas. Instead, it was likely a complicated series of events, involving dust, volcanic gases and how they conspired to wreak havoc on the global climate — perhaps even causing the oceans to become oxygen deprived ("anoxic").

"I still think that right now greenhouse warming and anoxia is the strongest interpretation" for why most plant and animal species died across the globe, said Keller.