JonF writes:
There are lots of scenarios and variations, but the bottom line is that most fossils are dated by radiometric dating of associated igneous layers, the association being established by various means.
You can probably tell us something about this, Jon. Apparently, there's a new way of using U-Pb dating directly on fossils themselves, which sounds very interesting to me.
Dating very late dinosaurs
From the article.
quote:
A laser beam unseats minute particles of the fossil, which then undergo isotopic analysis. This new technique not only allows the age of fossil bone to be determined but potentially can distinguish the type of food a dinosaur eats. Living bone contains very low levels of uranium but during fossilization (typically less than 1000 years after death) bone is enriched in elements like uranium. The uranium atoms in bone decay spontaneously to lead over time and once fossilization is complete the uranium-lead clock starts ticking. The isotopic composition of lead determined in the hadrosaur's femur bone is therefore a measure of its absolute age.
Could this improve accuracy all round from 1 Mya right back to the oldest fossils?
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