How do we know how old things are? That's a straightforward and very scientific question, and exactly the kind of thing students ought to ask; it's also the kind of question that has been muddled up by lots of bad information (blame the creationists), and can be difficult for a teacher to answer. There are a great many dating methods, and you may need to be a specialist to understand many of them…and heck, I'm a biologist, not a geologist or physicist. I've sort of vaguely understood the principles of measuring isotope ratios, but try to pin me down on all the details and I'd have to scurry off and dig through a pile of books.
Continue reading "Bones, Rocks and Stars" (on Pharyngula)