Their presence suggests that a massive comet or asteroid collided with the Earth, triggering the catastrophic collapse of life. The study, which also involved researchers from New York University and NASA, is featured in the February 23 issue of the journal Science. We can say with a good degree of certainty that there's a coupling of the two events. Where exactly the comet or asteroid hit is unknown. The impact 250 million years ago occurred during a time of extreme volcanism on Earth.
Volcanic eruptions can change climates in several ways.
Massive amounts of sediment and ash expelled during an explosion can block sunlight from reaching the Earth, causing a significant drop in temperature, inhibiting the photosynthesis that allows plants to grow, and causing food chains to collapse. Alternatively, carbon dioxide and other greenhouse gases ejected into the Earth's atmosphere by eruptions trap the sun's heat, sending temperatures soaring, and causing glaciers to melt and sea levels to rise. When these changes in temperature or sea level occur faster than a species can adjust to them, extinction results. If the species cannot adjust, they perish. But volcanism alone couldn't explain the rapid rate of extinction.