Which two substances do geologists use in radiocarbon dating
Next comes the question of how scientists use this knowledge to date things.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 we assume that the mammoth originally had the same number of carbon-14 atoms in its bones as living animals do today (estimated at one carbon-14 atom for every trillion carbon-12 atoms), then, because we also know the radiocarbon decay rate, we can calculate how long ago the mammoth died. This dating method is also similar to the principle behind an hourglass (figure 4).
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.
It’s assumed to be the same number of carbon-14 atoms as in elephants living today.
With time, those sand grains fell to the bottom bowl, so the new number represents the carbon-14 atoms left in the mammoth skull when we found it.
So if we started with 2 million atoms of carbon-14 in our measured quantity of carbon, then the half-life of radiocarbon will be the time it takes for half, or 1 million, of these atoms to decay.
The radiocarbon half-life or decay rate has been determined at 5,730 years.
Through photosynthesis carbon dioxide enters plants and algae, bringing radiocarbon into the food chain.