Once the half life of an isotope and its decay path are known, it is possible to use the radioactive decay for dating the substance (rock) it belongs to, by measuring the amount of parent and daughter contained in the sample.An important point is that we must have an idea of how much of the daughter isotope was in the sample before the decay started.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.These are the surfaces that we can get absolute ages for.For the others, one can only use relative age dating (such as counting craters) in order to estimate the age of the surface and the history of the surface.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.
It does burn in oxygen, and if you can pass the combusted gas through limewater, the carbon dioxide will turn the limewater milky by producing calcium carbonate.
This decay, or loss of energy, results in an atom (element) of one type, called the parent nuclide transforming to an atom of a different type (another element or another isotope of the same element), named the daughter nuclide.
For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter").
We have an activity in one of the PSI workshops "Exploring the Terrestrial Planets," that deals with this topic.
So, you can use the radioactive elements to measure the age of rocks and minerals. Their useful range is from about 1/10 their half-life (the time it takes for half of the radioactive element/isotope-- the parent, to convert into a non-radioactive element/isotope-- the daughter) to 10 times their half-life. You can use this to measure the age of a rock from about 128 million years to more than 10 billion years (the Solar System is 4.56 billion years old).