In reply to Jones Beene's message of Tue, 28 Nov 2006 20:11:58 -0800 (PST): Hi, [snip] > >--- Robin van Spaandonk wrote: > >> Same explanation. The 16O is produced preferentially >> during photosynthesis ... it can >> more easily attain escape velocity > >Then the average ratio on earth should be the same as >what has escaped (0.18 %)
How can you read and understand what I wrote, then come to exactly the opposite conclusion, based on it? What I said was that 16O preferentially escapes from massive bodies, leaving a higher concentration of 18O behind. However if this were the case, then one might expect the O in rocks (particularly the quartzes) to be nearer the interstellar ratio as this O is less likely to take part in atmospheric exchange. The O taking part in atmospheric exchange would primarily be in the air and water of the Earth. IOW the "ratio on Earth" would depend on who measured it, and exactly where they got the O from that they measured. BTW Google revealed a few interesting things: http://presolar.wustl.edu/~fjs/publications/p062abs.html http://www.sciencemag.org/cgi/content/abstract/259/5102/1733 http://www.agu.org/pubs/crossref/1995/94JA02936.shtml http://astro.nmsu.edu/~bwebber/high.html http://isotope.web.psi.ch/back.htm etc. >but it is NOT and in fact is >far different - that is the whole point ! > >The 18O/16O ratio in the interstellar region is >presumably what should have been the ratio found 4.5 >billion years ago on earth, and that has been measured >as 0.18%, however the actual planetary ratio is nearly > twice that level (0.3 %) which indicates that >somehow, in the earth environment, probably in the >ionosphere, substantial 16O has been converted to 18O >AFTER it got here from the sun ! Regards, Robin van Spaandonk http://users.bigpond.net.au/rvanspaa/ Competition provides the motivation, Cooperation provides the means.
