--- 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 %) 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 !
