MONDAY DECEMBER 23 - IMPACT CRATERS, PART 1
In a way, Chicken Little was right - the sky is falling, at least a little bit.
In its orbit around the sun, the Earth encounters tons of extraterrestrial material
each day. Most of this space debris burns up in the atmosphere, treating us to the
shooting stars and
Every so often, though, some of this extraterrestrial material survives the forces
and temperatures during the trip through earth's atmosphere, and reaches the surface.
Then we'd officially call it a
In very rare cases, these can get pretty
big - a few miles across, qualifying them as
asteroids - and upon impact, they
disintegrate but leave a
huge crater. Maybe you've even heard of the theory
that the dinosaurs were wiped when earth collided with an asteroid.
The earth is certainly not as cratered as the
but appearances are a bit
deceiving. Because the earth is bigger, it's actually been hit by about ten
times more objects than the Moon. Tomorrow night, I'll focus on some of these
encounters, and explain why there's not much evidence of them left on earth.