The largest volcanic event of the last 300 million years may not have been triggered by a meteor, researchers now say.

About 120 million years ago, as much as 1 percent of the Earth's surface may have been covered with volcanic eruptions. The origin of these massive 7-million-year-long eruptions in the Pacific Ocean, known as the Greater Ontong Java Event, has long been unclear, but some have suggested a cosmic impact as the trigger, smashing into the crust and causing lava to burst forth.

To see whether or not a meteor might have caused the Greater Ontong Java Event, scientists analyzed rocks from Gorgo a Cerbara in central Italy. This area was connected to the Pacific Ocean during the eruptions....