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What is especially interesting about these two L- and D-forms, at least for the purposes of this topic, is that the vast majority of living things only use the L-form.However, as soon as the creature dies, the L-amino acids start to spontaneously convert to the D-form through a process called “racemization”.What's more, racemization happens quite fast by geological standards, so, like the other methods of absolute dating we have discussed so far, dating by racemization cannot take us far back in geological time.
Also, the surface amino acids racemize much faster than the interior amino acids.This can only increase the potential range of error for age determinations.The local buffering effects of bone and shell matrixes are supposed to limit this effect, but it is still something to consider as potentially significant when acting over the course of tens of thousands to millions of years.So it would seem that if we want to know how long it was since an organism died, all we have to do is see how racemic its amino acids are. The process of racemization would have to go at a constant rate, and we'd have to know what it was. As a result, it isn't possible to say that racemization happens at such-and-such a rate. Suppose we examine a particular material (let us say tests of the foraminiferan Neogloboquadrina pachyderma) in a particular environment (let us say in mud in Arctic waters) and by comparing it with a dating method we know we can rely on, we establish that under these conditions racemization does happen at a reasonably steady rate.In that case we could use the foraminiferans to date sediment in places where we aren't able to use radiometric dating.