Radiocarbon dating of fossils
The oldest uncontested fossils on earth are 2 billion year-old stromatolites in Minnesota, Wisconsin, and Ontario.
Composed of layers of sediments laid down by colonies of cyanobacteria, stromatolites still exist, but are quite rare today.
If you hear of a carbon dating up in the millions of years, you're hearing a confused report. Second, they rarely contain any of the original carbon.
We can't date oil paints, because their oil is "old" carbon from petroleum. And third, it is common to soak new-found fossils in a preservative, such as shellac.
Scientist Olivia Judson provides this good example of what happens to an adult male gorilla in the tropical rainforests of the Congo; "An adult male gorilla— all 330 pounds of him—will be reduced to a pile of bones and hair within 10 days of his death.
What scavengers like vultures and hyenas leave behind, flies, ants, worms, and bacteria quickly consume.
If you know how pure your block of radium originally was, it's relatively simple to calculate how old it is by measuring how much radium is left.
This is a very useful tool if you have solid blocks of radium that need dating, but if you don't know how much radium was there in the first place, the job is a lot harder.
Each isotope is identified with what is called a ‘mass number’.
It is produced in the upper atmosphere by radiation from the sun.
(Specifically, neutrons hit nitrogen-14 atoms and transmute them to carbon.) Land plants, such as trees, get their carbon from carbon dioxide in the air. The same is true of any creature that gets its carbon by eating such plants. Suppose such a creature dies, and the body is preserved.
The atoms of some chemical elements have different forms, called isotopes.
These break down over time in a process scientists call radioactive decay.