Over at Pharyngula, PeeZee describe new kerfuffles involving tea partiers and creationists who weasel about the age of the Earth. He links to one of his earlier posts about Earth’s age, but I thought I’d add a useful link. It’s a nice short paper by geologist Robert Hazen, “How old is Earth, and how do we know?” published in Evolution, Education and Outreach (online access is free). All the dating methods are there: dendrochronology, varves, plate tectonics and—the method for determining Earth’s age—radiometric dating. There’s a good list of references, too.
If you’re a teacher, or someone who just wants a short precis on how we know that life has been around more than the Biblical few thousand years, bookmark Hazen’s piece. And, as I do, have a look at the journal from time to time.