BobDobbs Forager, Second Life asked:
How many dating systems like carbon dating are there and what age ranges are they suitable for?
Thereís quite a few, all of which are types of radioactive dating. They include potassium-argon dating, thatís useful for rocks over 100,000 years old. Thereís also uranium-lead dating, which has an age range of 1-4.5 million years old. It can be used for such long time spans because the half-life of uranium turning into lead is billions of years, in the order of the age of the Earth at 4.5 billion years.
Mike, from Cambridge, also called in to remind us about thermo-luminescence which can be used in pottery, also obsidian hydration and uranium trail dating when you observe the trails left behind by uranium decomposition.