We have an activity in one of the PSI workshops "Exploring the Terrestrial Planets," that deals with this topic.
We have rocks from the Moon (brought back), meteorites, and rocks that we know came from Mars.We can then use radioactive age dating in order to date the ages of the surfaces (when the rocks first formed, i.e. We also have meteorites from asteroids and can date them, too.It is impossible to predict when a given atom will decay, but given a large number of similar atoms, the decay rate on average is predictable.This predictable decay is called the half-life of the parent atom, the time it takes for one half of all of the parent atoms to transform into the daughter.On the other hand, the number of neutrons that can be contained in the nucleus can vary.
When the number of neutrons is in balance with the number of protons (which does not necessarily means that the number of neutrons has to be exactly the same as the number of protons) then the atoms of a particular element is said to be stable.The amount of time it takes for an unstable isotope to decay is determined statistically by looking at how long it takes for a large number of the same radioactive isotopes to decay to half its original amount.This time is known as the half-life of the radioactive isotope.While not a chemical test, the presence of carbon in a sample (like a meteorite) can be found by vaporizing the sample and passing it through a mass spectrometer.This is also a way to get at the abundance of the various isotopes of carbon.These differing atoms are called isotopes and they are represented by the sum of protons and neutrons in the nucleus. Carbon has 6 protons in its nucleus, but the number of neutrons its nucleus can host range from 6 to 8.