Xref: utzoo sci.astro:4074 sci.space:11455 sci.space.shuttle:3149 Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!apple!ames!xanth!aiko From: aiko@cs.odu.edu (John K Hayes) Newsgroups: sci.astro,sci.space,sci.space.shuttle Subject: Re: asteroid almost hits earth Keywords: By ice, smog, or fire? Check out Nat'l Geo Message-ID: <8914@xanth.cs.odu.edu> Date: 17 May 89 14:06:08 GMT References: <256@ringwood.Morgan.COM> <3200009@hpindda.HP.COM> <4566@tekigm2.MEN.TEK.COM> <2635@ssc-vax.UUCP> <103026@sun.Eng.Sun.COM> <6101@nfs4.rl.ac.uk> <1128@unm-la.UUCP> Reply-To: aiko@cs.odu.edu (John K Hayes) Followup-To: sci.astro Organization: Old Dominion University; Norfolk, Virginia USA Lines: 41 It just so happens there is an article in the current issue of Nat'l Geographic (June, I think) that deals with mass extinctions. It says that most scientists now believe that the extinction of the dinasaurs was caused by a single event as opposed to a gradual dying out. They define the time boundary of the Cretaceus (sp?) period (when there were dinasaurs) and the Tertiary (sp?) period (when there weren't) as the K-T boundary. There have been samples of quartz crystals found that date to around the K-T boundary that show signs of stress to a degree such as that caused by a nuclear explosion or an impact of a very large meteor. There has also been found a pencil thin layer in a chunk of rock of an element commonly found in meteors but rarely on earth. The layer in the rock where this occurs corresponds roughly to the K-T boundary. They estimate the meteor to have been about 6 miles across which would produce the equivilent of 10,000 times all the world's nuclear explosives. As for what happened after the impact, scientists differ. Some propose that 90 % of the earth's forests caught fire. Some say that if the impact were on land it would produce a thick smog that would cause extreme cold; but if it were at sea, it would send so much water vapor into the atmosphere that a greenhouse effect would produce extreme heat. One scientist who has been studying the Yellowstone fire proposes that even if the impact were at sea it would have produced an explosion so great that most of the world would have caught fire (I forget the specifics she detailed, but they were very interesting). Still others (but a minority now, I believe) maintain that the cataclysm can be explained by earthly causes such as ice ages, volcanic activity, shifting of the continents, etc. But, there seems to be evidence that suggests otherwise. -- ---{john hayes} Old Dominion University; Norfolk, Virginia USA internet: aiko@cs.odu.edu Home: (804) 622-8348 Work: (804) 460-2241 ext 134 <++++++++++++++++++++++++++++++++++> Are you a Have or a Have_Not? Because if you're a Have_Not, you've probably had it; whereas, if you're a Have, you've probably got it and are going to give it away at some point in the future! --- The Clash <++++++++++++++++++++++++++++++++++>