How long does a meteorite travel before it reaches Earth?
Many stony meteorites travelled through space as small rocks for a few million to tens of millions of years. Some iron ones travelled for hundreds of millions of years.
Before it fell, every meteorite was part of a bigger body, usually an asteroid. Then, one day, a collision knocked off a chunk, and that chunk began its long journey through space.
Scientists can measure how long that journey lasted. While a rock travels through space, it is hit by cosmic rays, tiny particles zooming through the galaxy. These rays change a few atoms inside the rock into special kinds of atoms. The longer the journey, the more of these atoms build up, a bit like how a clock's hands move as time passes. By counting them, scientists can tell how long the rock was flying alone.
The answers are amazing. Many stony meteorites spent a few million to tens of millions of years in space. Many iron meteorites, which are tougher and survive longer, travelled for hundreds of millions of years. Meteorites from the Moon often travelled for much shorter times, sometimes less than a million years, because the Moon is so close.
All this time, the rock was circling the Sun, slowly having its path nudged by planets, until finally it crossed Earth's orbit at just the wrong, or right, moment. Then, in a few seconds of fire, its journey ended.