Age determination
There are several ways to date things in nature; most of them use radioactive isotopes of one kind or another.
Isotopes of an element are atoms with the same atomic number (no. of protons), but with different atomic masses (protons and neutrons). Carbon (atomic number 6) for instance, is mostly made up of C-12, a tiny bit of C-13, and an itty-bitty bit of C-14.
Radioactive isotopes of an element are parent and daughter isotopes involved in radioactive decay processes. For instance, unstable K-40 turns into Ca-40 and Ar-40, while giving off gamma rays and electrons. The radioactive decay usually takes a loooong time. The time it takes for half the initial parents to break down is called the half-life. Different radioactive systems have different half-lives and are thus used for different age ranges.
| Isotopes | Half-life (Ga = billion years) | Age range (Ma = million years) | Minerals | ||||||||||||
| U-238/Pb-206 | 4.5 Ga | 10 Ma and up | Zircon, uraninite etc | ||||||||||||
| U-235/Pb-207 | 0.7 Ga | 10 Ma and up | Zircon, uraninite etc | ||||||||||||
| Rb-87/Sr-87 | 48.8 Ga | 10 Ma and up | Micas, whole rock | ||||||||||||
| K-40/Ar-40 | 1.2 Ga | 5,000yr and up | Micas, whole rock | ||||||||||||
| Sm-147/Nd-143 | 106 Ga | 0yr and up | Feldspars, pyroxenes etc | ||||||||||||
| C-14/N-14 | 5,730yr | 0yr-70,000yr | Organic matter |
So you can't really use carbon-dating for determining ages of Precambrian rocks... But if you look at the C-12/C-13 ratio of Precambrian rocks it might be possible to see where life began, since life very much prefers C-12.
Some radioactive systems, such as Rb-Sr and Sm-Nd, are not only used to determine the age of rocks but also their origin. Mantle rocks don't always like the same elements as crustal rocks and so the ratios between parents and daughters can be signatures of where the rock was formed.
But first you have to decide which rock to sample, and if you want to date the whole rock, mineral grains, or parts of mineral grains. After extracting the tiny amounts of isotopes from the sample, using one or several of the methods available, you have to engage mathematics and finally your own discretion and interpretative abilities to figure out how old this part of the Earth is.
Or maybe it's all just a hoax and the Creationists are right after all...