"Mass Extinction Before Dinosaurs--250 million years ago--Comet/Asteroid?

Becky, this extinction has been known about for a long time. It was more devastating than the one 65 million years ago that wiped out the dinosaurs. This one left only minimal life. The theory that is being proposed now is that a crater found (can't remember where) was on the opposite side of the planet from a super plume of magma (sorta the precursor to a massive volcano). The shock waves from the impact traveled around the world, re-converging on the opposite side, right near the super plume. This triggered massive eruptions, as all the violent power was released at once. I think it was the latest Scientific American that had an article about this, or maybe National Geographic. I'll check when I get home.

I think (if I'm not getting it confused with another extinction) that there is a layer with some advanced fossils. Directly above is a layer with an unusual chemical makeup, consistent with volcanic debris, but also containing traces of rare elements. Above this line, there are many fewer advance fossils.

David