timothym@tekigm2.MEN.TEK.COM (Timothy D Margeson) (05/23/89)
Hi, The current issue of Scientific American has an excellant article on the extintion matter. There have been extinctions of small and large scale every 26 million years since fossil records began in the precambrian epoch. Sometimes the extinctions appear instantaneous, other times they occur over millions of years. There is a new hypothesis about the dinosaur extintion that the impact of a large body into Earth would spatter superheated matter over a vast area of the planet. This with the fireball would superheat the atomospheric gases and ignite fires over 90% of the planets surface. Soot has been found in the iridium layer in several sites around the world. The article also points out that the 26 million year periodicity meets roughly with the rate at which the solar system moves through the arm of our galaxy and some correlation is plausible. The current rate of extintions is remarkable. The exact numbers escape me but are on the order of 1 per hour in the Amazon region. We ARE in one of the largest extinctions in the planets history. The largest extinction was one in which 90% of the oceanic life died. That particular extinction was hypothesized as caused by environmental change. What the article points out (and the Shuttle photos of the Amazon I just received) is that the current burning of forests and coal are making species drop like flys. The effects are not reversible. PS: those photos of the Amazon fires have to be seen to be believed. The smoke covers the ENTIRE BASIN, from the Andes in Columbia and Peru to the ocean and isle of Marajo. Look at a map for these places to see how large an area we are talking about. In one of the photos is a detailed close up of one fire plume estimated to be the size of all the Yellowstone fires combined - but this Amazon burn is for clearing purposes! The smoke is so dense over the basin that the sky probably can't be seen from the ground. Perhaps in the outer regions one could see the ball of the sun, but I'd bet you wouldn't have to squint. -- Tim Margeson (206)253-5240 PO Box 3500 d/s C1-022 @@ 'Who said that?' Vancouver, WA. 98668 e-mail replies to: timothym@tekigm2.MEN.TEK.COM
phil@titan.rice.edu (William LeFebvre) (05/23/89)
In article <4792@tekigm2.MEN.TEK.COM> timothym@tekigm2.UUCP (Timothy D Margeson) writes: >The current issue of Scientific American has an excellant article on the >extintion matter. So why is this stuff still being cross-posted to sci.space.SHUTTLE? Is the shuttle going to become extinct because of an asteroid? William LeFebvre Department of Computer Science Rice University <phil@Rice.edu>
ecphssrw@bob.csun.edu (Stephen Walton) (05/30/89)
In article <4792@tekigm2.MEN.TEK.COM>, timothym@tekigm2 (Timothy D Margeson) writes: >The current issue of Scientific American has an excellant article on the >extintion matter. Which I admit that I've not read yet. However: >The article also points out that the 26 million year periodicity meets >roughly with the rate at which the solar system moves through the arm of our >galaxy and some correlation is plausible. As the social scientists say, "Correlation is not cause and effect." It is difficult to think of anything which would happen *every* time the solar system went through a spiral arm which could cause extinctions on Earth. Contrary to popular belief, the steller density (stars per cubic parsec) in spiral arms is the same as between the arms; it is just that most of the new, hot, and therefore bright stars are in the arms, causing them to stand out. Yes, they have a higher concentration of dust and gas too, but it is more like 1 atom/cc instead of 0.1 atom/cc in the solar neighborhood. Not enough to make a difference. A dense molecular cloud *might* cause enough absorption to make the earth colder for a long period, but such clouds fill a small proportion of the volume of even a spiral arm. -- Stephen Walton, Dept. of Physics & Astronomy, Cal State Univ. Northridge RCKG01M@CALSTATE.BITNET ecphssrw@afws.csun.edu swalton@solar.stanford.edu ...!csun!afws.csun.edu!ecphssrw