214 million years ago an asteroid hit what is now Canada. Now the crater is a ring-shaped reservoir 70 kilometers in diameter: Manicouagan Reservoir.
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 this is 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, shown above. 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! It’s called the Central Atlantic magmatic province or CAMP.
So, this event could have put huge amounts of carbon dioxide into the air, causing an intense bout of global warming.
(I’m giving a public lecture on mass extinctions, so I’m boning up on them now.)
Azimuth 
The ‘public lecture’ link in the last sentence takes me to a much older post, probably not the one you intended.
Whoops! Fixed. Thanks.
I just read on an astronomy site a comment about how the Earth was, of course, bombarded as much as the Moon. We’re just as cratered as the Moon, but we’ve covered up the evidence over the millions of years since.
On a vaguely related note, congrats to the OSIRIS-REx team for retrieving bits of an asteroid. I’m looking forward to what they have to say about the sample.
It’s interesting to read about the Late Heavy Bombardment, a hypothetical period of increased asteroid impacts a hypothesized event thought to have occurred from approximately 4.1 to 3.8 billion years ago. But now Wikipedia says this theory is falling out of favor.