How long has Earth been hit by space rocks?
Ever since it formed, about 4.5 billion years ago. Impacts were much more common in Earth's early days and are rare today.
Earth has been hit by space rocks for its whole life, about 4.5 billion years.
Being born. Earth was actually made by collisions. Rocks, dust and small worlds kept crashing together until they built our planet. One of the biggest crashes, with a Mars-sized planet, probably made the Moon.
The busy early years. For hundreds of millions of years after Earth formed, there were many more asteroids and comets flying around the Solar System, and big impacts were much more common than today. The Moon's craters show this: most of them are more than 3 billion years old. Some scientists think a burst of impacts happened around 3.9 billion years ago, though this idea is debated.
Since then. Over time, many of the leftover rocks crashed into planets or were thrown out of the Solar System, so impacts became rarer. But they never stopped. About 66 million years ago, a huge asteroid hit what is now Mexico, linked to the end of the dinosaurs. About 50,000 years ago, an iron asteroid made Meteor Crater in Arizona.
Today. Small space rocks hit Earth every day as shooting stars, and meteorites land somewhere every day. Big, dangerous impacts are now very rare. Scientists watch the sky to find any large asteroids long before they could come close.