The radiocarbon half-life or decay rate has been determined at 5,730 years.Next comes the question of how scientists use this knowledge to date things.Since each beta particle represents one decayed carbon-14 atom, we know how many carbon-14 atoms decay during a month.
If we know what fraction of the carbon atoms are radioactive, we can also calculate how many radiocarbon atoms are in the lump.
Knowing the number of atoms that decayed in our sample over a month, we can calculate the radiocarbon decay rate.
If carbon-14 has formed at a constant rate for a very long time and continually mixed into the biosphere, then the level of carbon-14 in the atmosphere should remain constant.
If the level is constant, living plants and animals should also maintain a constant carbon-14 level in them.
And as far as we know, it has been forming in the earth’s upper atmosphere since the atmosphere was made back on Day Two of Creation Week (part of the expanse, or firmament, described in Genesis 1:6–8). Cosmic rays from outer space are continually bombarding the upper atmosphere of the earth, producing fast-moving neutrons (subatomic particles carrying no electric charge) (Figure 1a).1 These fast-moving neutrons collide with atoms of nitrogen-14, the most abundant element in the upper atmosphere, converting them into radiocarbon (carbon-14) atoms.
CARBON-14 IS CREATED (Figure 1a): When cosmic rays bombard the earth’s atmosphere, they produce neutrons.By comparing the surviving amount of carbon-14 to the original amount, scientists can calculate how long ago the animal died.Since the atmosphere is composed of about 78% nitrogen,2 a lot of radiocarbon atoms are produced—in total about 16.5 pounds (7.5 kg) per year.These rapidly combine with oxygen atoms (the second most abundant element in the atmosphere, at 21%) to form carbon dioxide (CO).This carbon dioxide, now radioactive with carbon-14, is otherwise chemically indistinguishable from the normal carbon dioxide in the atmosphere, which is slightly lighter because it contains normal carbon-12.The standard way of expressing the decay rate is called the half-life.5 It’s defined as the time it takes half a given quantity of a radioactive element to decay.