h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Very interesting article. I have heard ( but I don't known anyhting about )mentioned dating techniques such as Potssium/argon and Thermoluminescence. While I accept these are outside the title of your piece it maybe worth mentioning them in passing for completeness.

Lost Rhino

hmmmm, I only know a bit about this.

Potassium Argon dating is used by geologists. A potassium isotope decays to argon, by measuring the amount of argon gas trapped in the rock (relative to the amount of potassium) you can determine the age of a rock.

Thermoluminescence is a bit different. It works like the tags nuclear industry workers wear to monitor their exposure to radiation. When some materials (such as salt crystals), are exposed to radiation, electrons are exicited to higher energy levels and become 'trapped'. They stay there until the sample is heated, then they can escape and lose their energy by emitting light.
Thus when you heat such a material the amount of light it gives out is a measure of amount the radiation it's been exposed to. You can use this to date pottery and bricks as they are exposed to background radiation over the centuries, and the 'clock' is reset when they were first fired.