Earth's greatest hits
Ever since Earth formed more than 4 billion years ago, it's been pelted with rocks from outer space. Here are some of Earth's greatest hits:
212 million years ago
A comet that shattered into small pieces may have created five large impact craters on Earth, including one of the largest known on land, the 100-km- (62-mi-) wide Manicouagan crater in Quebec, Canada. The impact may have caused the extinction of about 80 percent of species on Earth.
65 million years ago
An asteroid about 10 to 20 km (6 to 12 mi) in diameter slammed into Mexico's Yucatan Peninsula and wiped out half of Earth's species, including dinosaurs.
3 million years ago
An underwater crater 89-km (55-mi) wide formed when a 1.6-km- (1-mi-) wide asteroid smashed off the coast of Virginia.
49,000 years ago
The famous Meteor Crater in Arizona may be all that's left of a 46-m (150-ft) meteorite that slammed into Earth.
90 years ago
An asteroid exploded above the Tunguska Valley in Siberia, flattening more than 2,000 sq. km (800 sq. mi) of forest and killing hundreds of reindeer.