Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: OmnipotentOne on 05/06/2004 17:54:39
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I remember reading some where that ever 26 million years theres a mass extinction ........WHY?? I cant seem to remember but is it because we come between some planets orbit, and get effected by asteroids, or huge amounts of radiation? Could this possible be avoided? [xx(]
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I think its to do with either:
1. As you said, meteors and asteroids. This could be to do with the orientation of the planets - maybe that's when we are furthest/closest (i can't decide which!) to jupiter, meaning that we are far more likely to be hit by a foreign object. Or, its just down to probability, and on average, one large chunk of rock hits us every 26 million years
2. Ice ages. Maybe due to the Earth's orbit, we get a super severe ice age.
3. God (but we don't like to talk about that possibility).
"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
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Kind of off topic, but I just finished reading a cool book called Calculating God (by Robert Sawyer) that was about an alien race coming to earth to talk to a paleontologist about mass extinctions that happened both on earth and on their home planet at the exact same points in the universal timeline. (as well as on a 3rd race that was travelling with the aliens)
It was a fun read and an interesting way of looking at the universe's origins, albeit fictional.
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The mass extinctions that have been studied so far have been caused by large impact events, but I've never heard that there is a regular cycle to them. We are now in one of the largest mass extinctions the earth has ever endured.
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John - The Eternal Pessimist.
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Supposidly there have been 5 mass extinctions so far, and each one wiped out 2/3 of the earths population....Yeah i think it has to do with the earths unfortunate orbit into some large asteroid field. They tryed to prove this when they found high levels of Iridium(SP??) deep in the earth, an element not common to this planet but is found to be highly concentrated in asteroids. Im gonna go celebrate my new found knowledge with a bottle of coke! cheers [:D]
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quote:
Originally posted by OmnipotentOne
Supposidly there have been 5 mass extinctions so far, and each one wiped out 2/3 of the earths population....Yeah i think it has to do with the earths unfortunate orbit into some large asteroid field. They tryed to prove this when they found high levels of Iridium(SP??) deep in the earth, an element not common to this planet but is found to be highly concentrated in asteroids. Im gonna go celebrate my new found knowledge with a bottle of coke! cheers [:D]
I have to disagree slightly- the earth's orbit may not be circular, but it is not eccentric enough to reach the asteroid belt, which is between Mars and Jupiter! I think thats its just down to chance of being hit by a foriegn object - nothing happens "regularly" over very large periods of time- there are simply two many external factors for anything to have a period of 26 million years...
"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe
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I read somewhere about a gravitational resonance between Saturn Jupiter and Earth, that could tip the Earth's axis over about 75 degrees. The time period for this was ~20 million years. I haven't been able to recover that reference, but I did find this, a reference to an article published in "Nature", that discussed this phenomenon:
http://www.xs4all.nl/~carlkop/klimapla.html
As an aside, these same researchers claim that the earth's rotation about the galactic center causes gravitation tides in the mantle, which is the cause of supercontinent formation, with a time period of 400 million years. The orbital period of th galaxy is about 200 million years, so 2 periods is required to form, breakup, and reform the supercontinent.
I can'r say if it's true, but it does show that there are long term cyclic effects on the earth.
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quote:
Originally posted by OmnipotentOne
Iridium(SP??)
That is the correct spelling my friend! Impacts are associated with Iridium deposits (many found in Ice cores. Studies on the meteorite thought to have facilitated the demise of the dinosaurs also used spores from ferns as an indication. Ferns are the first plants to re populate and thus there is a spike in spores discovered. (Er, sorry this isn't really physics, i got carried away)