Why asteroids collided with earth when humans didn't exist, why don't  they fall on earth now?
494590
well, billions of years ago, when stars and planets were forming, there were millions of rocks floating around. So space was pretty crowded back then. Now they are all space out, it's very rare we will get hit.
363001
Some people think its because of the moon. The theory is that a huge asteroid hit the earth and then bounced of into orbit around the earth. This supposedly caused the earth to have a tilt to its axis.
382749
are they sure that it will hit earth in that year? Maybe it will hit earth much later, or maybe they'll find a way to stop it. I don't know, the size, but asteroids sure are large, but maybe it'll be just a small collision that the earth will not split up and humankind will not be...destroyed.
139768
By the time that happens the Earth will have already been destroyed by the sun. But if the Earth was still around, it is highly unlikely that we would collide with any matter at all, since space is mostly just dust and emptiness, believe it or not. We would likely have a higher-than-usual amount of dust moving about the solar system, however.
646581
Undoubtedly our moon has been impacted by asteroids and other objects that otherwise would have struck Earth. If the moon wasn't there, then it follows that we might be struck more frequently.
970160
Yes, I do because Earth is not a closed system. If it were, meteorites would never hit.  I have an interesting comparison (to me at least)  about comets "seeding" the earth....... have you ever noticed that earth resembles an "egg" and comets resemble sperm?  they have heads & tails like sperm...... and the term panspermia......... just a thought.......
891496
the first 2 answers are sadly wrong, were you around in 1995 when shoemaker-levy 9 hit jupiter,  the asteroid was what is called a "rubble pile".  a collection a rocks all held together by there mutual gravity till the stronger pull of jupiter pulled it apart into a dozen pieces. when SL9 hit the gas giant astronomers on earth thought nothing would happen.  that the rocks would just slip into the clouds and be gone,  but thats not what happend.\n\nmassive plooms of material were ejected hundreds of miles up into space leaving behind large dark spot on the surface clouds of jupiter that were still there for several years.  check out the link for pics of the aftermath.  each dark spot is the size of the earth
1023987
They don't have to. Yes, there are thousands of asteroids, but space is really, really big! The asteroids are so far apart that you could just randomly fly any path through the belt and never see one. They actually have to carefully plot a course to rendezvous with one if that is the goal of the mission, like NEAR or Hayabusa.
209347
"...Small stones to a few millimeters in size are slowed down so much by the atmosphere that they end up drifting slowly to the ground. \n\nPieces of space rock of a few millimeters to a few centimeters burn up completely in the atmosphere of the Earth before they can reach the ground, and can be seen at night as falling stars. If it is sufficiently dark and clear outside, then you can see a few falling stars every night. \n\nIf the rock is bigger, then part of it can survive the trip through the atmosphere and reach the ground as a meteorite. If the stone weighs less than a few tons, then it doesn't fall very fast anymore in the end, and it makes a small dent in the ground.   "\n\nhttp://www.phys.uu.nl/~strous/AA/en/antwoorden/meteorieten.html
796556
The earth and human race can be eliminated by various things, both internally and externally. Internaly our earth could lose heat and use up valuable resources due to pollution and over production. Externally comets and meteors could crash into earth. The sun wont blow up for a few more million years so you dont have to worry about that.
792195
Interesting question.  You can extend it - why does the Earth continue to turn on its axis?  And circle the sun?  Why does the sun circle the center of the galaxy?  Why do things keep going, year after year for billions and billions of years?\n\nNewton thought about this and came up with one of his famous laws:  Without an external force, a body in motion stays in motion, a body at rest stays at rest.\n\nThe second half is easy.  Put a rock on the floor and it will stay there forever until you pick it up.  It won't move without an external force.  So what if you shoot a bullet into the air.  We all know it falls back, but why?  Because the force of gravity acts on it.  Take away gravity and it will still stop.  Why?  Because the friction of air on the bullet's surface will slow it down and finally stop it.  Take away air, take away gravity, and the bullet will go on forever.\n\nSo to answer your question:  Simply put, the asteroids have no forces to stop them.  Gravity keeps them trapped around the sun, but they outside of the range where they fall in, so they simply continue to go around, just like the planets such as Earth.  The asteroids started in motion at the formation of the solar system 4.5 billion years ago, and except for random collisions that altered courses and accelerated (or decelerated) the rocks, no force has acted on them to slow them down.  A perfect example of Newton's law, even more amazing because Newton did not know of the existence of asteroids.
962669
Space debris has become a growing concern in recent years, since collisions at orbital velocities can be highly damaging to functioning satellites and can also produce even more space debris in the process, called Kessler Syndrome. Some spacecraft, like the International Space Station, are now armored to deal with this hazard. Also astronauts on EVA are vulnerable; see Extra-vehicular activity.\n\nThe first verified collision with catalogued space debris occurred in 1996, tearing off a boom from the French satellite Cerise.\n\nClouds of very small particles are not as serious but cause erosive damage, like sandblasting.
651683
its the most disastrous formula humans have ever concocted. gods are fake & politics are inherantly corrupt. we concentrate so much on these two silly notions that we failed to progress as a spiecies. theres an asteroid that will solve all our problems some day. had we focused on right than wrong, we could have stepped out of harms way.
919998
Momentum, p=mv and the asteroid itself is the example.  Its momentum was too great to stop with the nuclear weapons, which is the reason it was broken up instead.  This gave the fragments new vectors for v, such that they passed the earth.\n\nFluid friction was exhibited in the oil flow shown earlier in the movie.\nWithout friction, the geyser would have been much higher above the pipe and a much smaller diameter pipe would have been sufficient.
21269
It would take a very large asteroid to hit or pass near the Earth to shift the Earth's orbit suddenly.\n\nIf it passed near the Earth, that asteroid's gravity could pull the Earth and alter its orbit around ths sun, but it would have to be enormous to have a significant impact on the orbit in such a brief encounter - perhaps as big as some of the smallest planets.\n\nBut after billions of years, most of the large objects around the sun have settled into stable orbits.\n\nAnd small asteroids and comets pass by the Earth all the time without much change.
1164830
Oh Boy! got it right. The larger asteroids are also basically spherical. This is ultimately due to the fact that they have enough mass for the gravity to force them into this shape. Of course, there are irregularities, but they are fairly small except for the bulges caused by rotation. The smaller asteroids don't have enough mass for the gravity to have much effect.
509642
Earth isn't in a strong enough gravitational pull of another planet. There is no "up" or "down" in space. Earth is constantly moving, the solar system moves, the galaxy moves. \n\nI have a question for you...\nHow would you define which direction we would fall in space? Gravity is the reason we fall on Earth.