Asteroids have been hitting the Earth for its whole existence, particularly during the “Late Heavy Bombardment” period around 4 billion years ago; this would have made it difficult for life to get started at all.
There are more smaller rocks than there are larger ones heading towards the Earth.
We are always being struck, with over 100 metric tons of matter entering the atmosphere every day, most of which is in the form of dust or sand grain-size meteors, which are the ones we see as shooting stars.
This simulation by the Discovery Channel has provided a visual scenario of what would happen if a larger asteroid collided with Earth:
The Spaceguard Center was started so it could find and follow as many near-Earth objects (NEOs) as possible. Each time an asteroid is found that’s not going to hit the Earth, the calculated odds of the Earth having an impact goes down.
By the time the survey is completed, the odds of dying in an asteroid impact will decrease by a factor of 10, from 1 in 70,000 to 1 in 700,000. This is assuming that they don’t find one that is going to hit.
Here is a short video from NASA’s Jet Propulsion Laboratory showing all their asteroid/comet observations; it’s a little scary to know.
When we talk about an extinction level asteroid, we imagine some huge rock comparable to Earth, but in fact, it only has to be approximately 3 to 10 miles across. If you think that’s bad just think, an asteroid just needs to be big enough and it could send large amounts of dust into the atmosphere, and that would lead to an abrupt change in the climate that would cause a global catastrophe.
Dr. Carol Raymond from JPL talks about iur current understanding of NEOs:
There is an asteroid called Apophis that is 886 feet across that will miss that Earth, but will be within the orbit of our communication satellites, and that’s close.
There were 556 bolide events between 1994 and 2013, according to NASA’s Jet Propulsion Laboratory. The Chelyabinsk meteorite hit the Earth with considerable force. Lucky for us, most don’t make it through the atmosphere.
I’m sure NASA and the powers that be are working out all kinds of ways to “shoot” an asteroid to save us all, and I’d be really interested in what they come up with.