It’s thought that asteroids were forged in the same high energy crucible that gave birth to our solar system. These rocky bodies range in size from small pebbles to enormous hunks of stone measuring hundreds of miles across. Along with the Sun, planets and moons, their creation came about approximately 4.6 billion years ago when an enormous molecular cloud containing dust and gas collapsed in on itself.
As such, small pieces of asteroids and other space rocks occasionally fall to Earth. Although most burn up in the atmosphere as “shooting stars,” occasionally – around ten times a year – a small piece known as a meteorite makes it to the surface. As a result, meteorites often leave a small impact crater. Unless you have the cosmic misfortune of being hit by one, however, they pose no serious threat to human life.
An asteroid the size of Bennu is another matter, however. The impact of such a large space rock would unleash kinetic energy equivalent to tens of thousands of atomic bombs. The shock waves would cause earthquakes and tsunamis. And the dust cloud would probably cool the planet for hundreds of years, devastating its ecology.