Is this "idea" of an asteroid colliding with earth really true?

Question

Is this "idea" of an asteroid colliding with earth really true?

Answer 1

We think an asteroid collided near Cancun 20 million years ago and killed all the dinosaurs.  An asteroid hit Siberia in about 1910 with the power of several atomic bombs.  The idea is certainly plausible.

Answer 2

It's not just an "Idea", it has happened many, many times.  

Scientists have discovered well over 200 impact craters of different ages around the Earth.  Most of them have been heavily weathered away or buried over time.  However, some are fairly obvious.  Here are pictures of a few:

The 200 million year old Manicougan Impact crater in Quebec:

http://www.lpi.usra.edu/publications/sli...

The "Wolfe Creek" impact crater in Australia:

http://www.unb.ca/passc/ImpactDatabase/i...

and, the most famous, Meteor Crater in Arizona (roughly 25,000 to 50,000 years old)

http://www.meteorcrater.com/index.php

So, the Earth has been hit in the past.  Indeed, it has been hit many many times.  

It is sobering to look at a photo of the moon...

http://www.astrosurf.com/cidadao/moon_99...

... and realize that each one of those giant holes (the most of the distinct ones in this photo are 10s of miles across) was formed by the impact of an asteroid on the moon.  The Earth, being larger, has been hit as many, if not more, times than that.  

It is not a matter of IF the Earth will be hit again by a large object from space, but WHEN.   Currently, as best we can tell, the odds that a dangerously large rock from space will hit is very low.   No current asteroid known is thought to have more than a microscopic chance of hitting us any time within any of our lifetimes.  

However, given enough time, and given the amount of stuff out there, it WILL happen again someday.

Answer 3

There's plenty of evidence that asteroids have hit the Earth in the past. They didn't happen all at once, and there's every reason to believe that it will continue happening in the future.

You've got the word "idea" in quotes, as if you don't believe it.  In science, you don't believe or disbelieve anything.  You look at the evidence, and it either suggests an idea is right, or it suggests an idea is wrong. And in science, most of these ideas turn out to be wrong.  But when there is enough evidence, and an idea still isn't wrong, it's customary to call it a theory, and treat it as fact.  But let's use another example.

Suppose that you go outside and happen to notice that the horizon is pretty straight.  You think "That's just what it would look like if the world was flat."  It's a guess, but there's some evidence that it's correct.  And that's how scientists form an hypothesis. So, you go home, and you tell your parents of your discovery.  They say, "You didn't have to look.  Everyone knows the world is flat."  And you gain confidence in your hypothesis, having checked with the experts.  But a couple months later, you've climbed a mountain, and from the top, the horizon doesn't look quite so straight anymore.  But looking carefully, you notice some small color anomalies, and you think, "Oh, yeah.  The atmosphere is acting like a lens - and this is just chromatic aberration. Oh, and we know that a lens can distort things, and besides, we already know the horizon is straight."  Your faith in your hypothesis is strengthened, mostly by the big words you used.  Laugh if you want, but this is how science is done.

A few months go by, and you hook up with a girl in India in an internet chat.  At one point she mentions that it's really late at night, and has to go.  But for you it's day time. You trust her, but you imagine that she's on the other side of the world.  The world is flat, and one side is night. Well, things develop, and you book a flight to India to meet this girl in person.  On the way, you carefully watch out the window for the edge of the world, but you never see it. Your faith in this flat Earth model is shaken, not stirred.

You've been back home for months, and you see a total eclipse of the Moon.  These events are quite common, and you've seen three of them before.  You see the round shadow of the Earth cross the face of the Moon. It was round each time you saw it. You conclude that the Earth must be a sphere to always cast a round shadow on the Moon.  You tell your parents this, but they spank you.  You decide to elope with that nice girl in India.  But by the time you get there, her parents have married her off.  And that's when you start to develop your first truly scientific theory of the world.  The world isn't flat after all.  The world is really messed up.

Answer 4

of course, it happens all the time exept most just burn up in the atmosphere

Answer 5

Well, the "idea" that nothing bad is ever going to happen again starting from now on is nice, but not reality. Asteroids seem to be tracked fairly well in their clusters between Mars and Jupiter. Others, near Saturn and out towards Neptune seem to have stable orbits as well. But it is the Comets we can't see that are the problem. They reside out beyond Pluto where it's too dark to see, the Oort cloud for instance. Some Comets have a regular period which sends them streaking at the Sun and bits of debris could fly off and produce meteorites here on Earth. Others, have irregular periods and could conceivably head near enough to the Earth on their way to the Sun that would cause catastrophic damage, not to mention a direct strike on the planet. Ancient manuscripts describing the myths and legends of gods and goddesses doing battle in the air causing cataclysmic damage on Earth could be evidence that Earth has been hit before.

But I'm with you, I don't think about what horrible things might happen to the world when I wake up in the morning. I'm just glad I made it through the night and get ready to face another day.

Answer 6

Look at the moon if you think impacts don't happen.  It's loaded with craters from asteroid and comet collisions.  On Earth there are over 200 craters that haven't been wiped out due to erosion and weather.