Close Call Coming: Scientists are concerned that a large asteroid or comet could strike Earth, causing catastrophic damage. One 1,000-foot-wide object, the 2004 MN4, will miss Earth by just 25,000 miles in 2029.

Striking Earth

Each day...
• 25 tons of dust and sand-size particles burns up entering the atmosphere.

About once a year...
• A car-size asteroid hits Earth's atmosphere but typically burns up before reaching the surface.

Every thousand years or so...
• An object the size of a football field hits Earth and causes significant damage to the impact area.

Every few million years...
• If an object larger than 0.6 miles across struck Earth, it could cause mass extinction and threaten civilization.

Some Past Impacts

Meteor Crater
An 80-foot-diameter asteroid hit what is now Arizona 20,000 to 50,000 years ago to form a crater three-quarters of a mile wide. It was the first crater identified as being caused by an asteroid impact.

Manicougan Crater
A massive object struck what is now northern Canada about 210 million years ago to create a 60-mile-wide impact crater. The impact probably created a massive fireball and ejected material that reached around the world.

Chicxulub Crater
An enormous asteroid or comet struck what is now the Yucatan Peninsula in Mexico more than 65 million years ago. The event has been linked to an extinction of more than half of Earth's species. The 112- to-186-mile-wide crater is buried under thousands of feet of limestone.

SOURCE: NASA Jet Propulsion Laboratory | THE WASHINGTON POST


© 2005 The Washington Post Company