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Re: Re: Severity Of Asteroid Impact

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Posted by Alexander on February 13, 2001 19:19:41 UTC

Gravitational energy of Earth (i.e., energy to tear the Earth apart) is E=(3/5)GM2/REarth = 3.8x1032 Joules, which is much more than, say small 1-km 6x1012 kg asteroud
moving with 30 km/sec : Easter = 5.4x1021 J = 1.35x106 megatons of TNT (about a million of small hydrogen bombs, or hundred thouthands of good ones), so Earth gravitational energy is about 7x1010 times more than the asteroid's kinetic energy.

So, nothing happens to Earth itself.

Now, because this energy is released NOT all over the Earth, but in only few cubic kilometers around the impact point, the DENSITY of this energy around there is very high: about 540 MegaJoules per liter, which is 55 electronvolt per atom, or about 0.6 MegaKelvin of temperature. This explains local effects: evaporation and ionization of the impact site and asteroid, then resulting fireball a few hundred miles in diameter, earthquake with 14+ magnitude, etc.

Now about global effects. Because the atmosphere acts as a wavegide, the shock wave energy of the fireball does not dissipate much and thus the shock wave circles the globe a few times, crushing all around (fragile life forms mainly). Same, by the way, is partly correct for a seismic shock wave in a litosphere - it travels around the globe (faster than airblast) shaking everything and cracking crust all over. Tsunami wave in ocean/lakes is a consequence of the seismic wave. And it also does not dissipate much intil it hits island or shoreline.

After much of vegetation and fauna in a thosand mile radius around impact site is burned out in a good firestorm, there is plenty of ash lifted with hot air high up in the stratosphere. Fast jets in upper atmosphere spread it over the globe in a few days. It becomes dark almost everywhere. Ash reflects sunlight back in space rather good, and not much of it penetrates to the surface of Earth. Temperature of surface and thus the air around drops quickly (in a matter of few days), and remains very low (well in sub-zero F range) for many months, till extremely fine ash dust particles settle around. So during this "induced winter" much of flora and fauna of the other side of the globe dies.

Ocean life as being better protected dies in less persentage, but still not too many species could survive in freezing waters (likely covered with ice).

So, you may see that it does not take much of energy to essentually damege or shift ecosystem. Earth will be still there in its round shape, orbiting Sun at the same distance, but some (if not most) species may not make it. Later, in a few tens to hundreed years when ash settles completely and everything returns to normal, vegetation will cover back damaged and dead areas and there will be plenty of food for certain survivers, and those multiply and may take over in the ecosystem (say, mammals instead of dinosaurs).

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