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 =
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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