Space rocks will have colided with the earth before Homo-Sapians exsisted so it is, unfortunatly, impossible to calculate.
But it's happening all the time ... small ones, that is.
meteorites are rocks that hit the earth meteors have not
Comets are the rocks that hit the earth during formation of oceans...
Rocks that hit the Earth's surface are called meteorites. When a meteoroid (a rock in space) survives its journey through the atmosphere and lands on the Earth's surface, it is referred to as a meteorite.
There's nothing special about it; they are just falling rocks. Of course, they are rocks that fall FROM SPACE, and the Earth is just sort of "in the way" as the rocks are falling around the Sun.
Rocks from space, known as meteoroids, do strike Earth, but most burn up in our atmosphere, becoming meteors or shooting stars. Larger meteoroids can survive the journey and impact Earth, but the chances of a direct hit on a populated area are extremely low due to Earth's vast surface area and sparse population density.
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Meteoroids are small chunks of rocks and debris in space that travel through Earth's atmosphere and hit its surface.
A "meteor shower". (The individual space rocks pulverize or vaporize when they hit Earth's atmosphere.)
Meteoroids. Meteorites are stones that hit the surface and meteors are just rocks in space.
Earth is hit by rocks (meteorites) every day.
In the beginning of the history of the solar system the Earth was bombarded frequently by asteroids. Now the frequency has diminished significantly but still many tons of "space rocks" fall into the Earth's atmosphere each year some of these hit the ground.
Gravity. Meteors are nothing more than "falling rocks". There are probably BILLIONS of stray rocks floating around in space. Many of them are in the vague region between Mars and Jupiter known as the "Asteroid Belt", but that still leaves plenty of things floating around in space between the planets. Some of them get close to the Earth, and some of them hit us. Most are small, but a few times per year, larger things hit; and every few centuries or so, something large enough to cause significant damage hits the Earth.