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.
From a graphic accompanying an article in The Washington Post on scientists keeping a lookout.