[meteorite-list] Phil Bland Article
From: Sara Russell <sarr_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:13 2004 Message-ID: <E14Y92S-00025N-00_at_pat.nhm.ac.uk> >From Phil Bland >Here's the latest installment: > >Sterling, >I'm interested to see where the 500 per year number came from, as I've also >seen it bandied about but hadn't known its history. I also quite like the >idea of using impacts on dogs and humans! As you say, it's methodologically >sweet. However, I think that whichever method we choose we'll be doing very >well to get the errors below about a factor-of-two. That was Halliday's >estimate for MOPR, and our's is probably similar, so its worth keeping that >in mind when making a comparison - 23,930 and 20,000 are identical when this >error is taken into account. Although in one of his early papers he >calculates flux at the top of the atmosphere, later on most of Halliday's >estimates are given as a flux to the ground surface, so they're directly >comparable to ours and yours. It's worth also bearing in mind that when >looking at even the recent history of estimates of meteorite flux, >differences of several orders of magnitude were common. >I think the difference that you note between the flux of individual >fragments and the meteorite as an intact rock might well be the source of >some of the discrepancy. We worked quite hard to remove the fragmentation >problem from our study, just because it may be partly produced by local >weathering. But a look at your average meteorite fall gives you an idea of >just how many fragments can result. I think Buchwald does some review of >this in his book. > >Stream flow,a nd transport of meteorites, is something we thought about. In >the Sahara, it may be problem when considering older samples, although there >might be ways around this by restricting yourself to younger meteorites. In >the Nullarbor at least we can effectively discount it. There have not been >active streams there for >100,000 years, and in addition, many meteorites >(e.g. Billygoat Donga) are found with numerous weathered fragments clustered >together over only a few 10's square metres, suggesting that weathering >frgaments the meteorites, but the fragments aren't transported far. >You're right about the Esquimaux using irons, and in Australia there is >plenty of evidence that they use tektites as cutting tools, but no evidence >that they've ever used meteorites. Alex Bevan wrote a neat paper on this >actually, and he also has something to say on the problem of the small >number of recovered irons. We also have a small number of irons in the >Antarctic population, and there's no chance that any locals have made use of >them there, but interestingly the overall percentage of irons seems to be >similar between Antarctica, and the different hot desert populations. A >simpler explanation may be that the fall population is just slightly out - >falls are reported as falls when the meteorite is recovered, not if someone >only sees a fireball and fails to find the meteorite, and it's a lot easier >to recognise a lump of metal as something unusual. It's just a thought. > >If you have any problems getting hold of any papers - my stuff or anything >else - just let me know and I'll be happy to send you copies. > >best wishes, > >Phil > > Received on Wed 28 Feb 2001 11:01:16 AM PST |
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