Hi Again: I found it!
It (the impact cross section) is (I should have realized) incoming velocity dependent. For objects going at 50 km/s the cross sectional area of the Earth is increased by 5%. However, for something approaching at 25 km/s, this increases to 20%! For something going really slowly relative to the Earth (catching up), the impact cross section can be more than double the actual cross section of the Earth Larry On Mon, December 17, 2007 10:34 am, E.P. Grondine wrote: > Hi Sterling, list - > > > Thanks for clarifying the impact crater situation, > though I am still sceptical about the models of Moon impact rates and Earth > impact rates. > > I know that the Moon absorbed some impactors that were > headed for the Earth - at least it did so within human recorded memory, and > if anyone wants proof of this, contact me off list and I'll you a copy of > the Trempeauleau petroglyph. > > > So at a minimum the Earth cross section needs to be > reduced in modeling the combined Earth-Moon system. My guess is that this > should reduce the impact rate/craters by about 10%, leaving say only 2.7 > million or so craters. (Imagine that, E.P. arguing for a lower Earth > impact rate!) > > Could you give us the quick math for this? I can't do > it myself anymore. > > I was also quite surprised by this cratering model you > pointed to: > > http://www.news.uiuc.edu/scitips/02/1025craters.html > > > given that the KT-fossil meteorite is carbonaceous chondrite, in other > words a comet, and that the Sudbury impact appears to have been iron, as > its remains are a source for our nickel steel. It seems likely to me that > this Illinois team's computer model is off. > > Re: the apparent 31,000 BCE impact, my hope is that > large irons may have survived in "defraction lenses" (is that the right > term?) in the blast, irons large enough to survive later weathering. > Trying to remember > the find spot for the mammoth tusks, I seem to remember it was reported > that they came from a shop in Calgary, further unknown. > > > good hunting all, E.P. Grondine > Man and Impact in the Americas > > > > > > _________________________________________________________________________ > ___________ > Looking for last minute shopping deals? > Find them fast with Yahoo! Search. > http://tools.search.yahoo.com/newsearch/category.php?category=shopping > ______________________________________________ > http://www.meteoritecentral.com > Meteorite-list mailing list > Meteorite-list@meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > > ______________________________________________ http://www.meteoritecentral.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
