Conversation

214 million years ago an asteroid hit what is now Canada. Now the crater has become a ring-shaped lake 70 kilometers in diameter: Lake Manicouagan.

Did this impact cause a mass extinction? The asteroid was 5 kilometers across, while the one that killed the dinosaurs much later was 10 kilometers across. But that's still huge!

For a while people thought this impact may have caused the Triassic-Jurassic mass extinction event. But now that the crater has been carefully dated, they don't think that anymore. The extinction happened 12 million years later!

In the Triassic-Jurassic mass extinction, all the really huge amphibians died out – like Mastodonsaurus, which was 6 meters long! So did lots of large reptiles. This let another kind of reptile – dinosaurs – become the dominant land animals for the next 135 million years.

So what caused this mass extinction? A mass extinction event is like a crime scene: you see the dead body, or more precisely the *absence* of fossils after the event, and you see other clues, but it's quite hard to figure out the killer.

One big clue is that there was an enormous amount of volcanic activity near the end of the Triassic and start of the Jurassic, as the supercontinent Pangaea split apart. It lasted for about 600,000 years. In fact, there's about 11 million square kilometers of basalt left over from this event, spread over the eastern Americas, western Africa, Spain, and northwestern France! So, this event could have put huge amounts of carbon dioxide into the air, causing an intense bout of global warming.

For more try these:

https://en.wikipedia.org/wiki/Triassic%E2%80%93Jurassic_extinction_event
https://en.wikipedia.org/wiki/Central_Atlantic_magmatic_province

(Soon I'll be giving a talk on mass extinctions.)