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What would happen if a comet hits Earth?
Answer 1:

Well, this depends first and foremost on the size (say diameter) of the bolide. There are two basic types of bolides: asteroids (rock plus metal) and comet ( ice plus rock).

Each DAY the earth gains about 200 metric tons of space debris. One ton is 1000 kilograms of mass. Hence, each day the Earth picks up about 200,000 kg of stuff. Most of it rains upon the surface as tiny particles called dust or spherules. Occasionally an object is bigger, the size of typical rocks (a few kilograms). Very occasionally the object is a meter or two. About once every 100 million years a 10 km diameter object impacts Earth.

The smaller objects are slowed by friction in the atmosphere and free fall to earth at a speed that depends on their shape and mass -typical rates are a few hundred meters per second; these leave tiny depressions. The bigger objects, of the order of football sized come through the atmosphere and do not experience too much deceleration, they impact the surface at the same speed that they encountered the earth -typically 15 to 25 kilometers per second. NOTE 20 km/s = 45,000 mph!

These space rocks are traveling at 40,000 miles per hour! That means a distance from Santa Barbara to Los Angeles California in a fraction of a second! Faster than the blink of an eye!

When a large object, bigger than 100's of meters hit the surface of the Earth at that speed (40,000 miles per hour), a planetary wide disaster unfolds. Rocks melt and turn into gas, a huge amount of dust; 'tidal waves’ can develop when impact occurs in the oceans.

65 million years ago a ten kilometer object hit the earth at the Yucatan peninsula in Mexico. This impact killed 90% of all life on the planet and created a thin layer of debris all over the planet. It was dark for six months and the oceans became somewhat toxic for a while. If this happened again today, civilization would be wiped out -probably no one would survive.

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