As soon as it dies, however, the C ration gets smaller.

Carbon 14 is continually being created in the Earth's atmosphere by the interaction of nitrogen and gamma rays from outer space.

Since atmospheric carbon 14 arises at about the same rate that the atom decays, the Earth's levels of carbon 14 have remained constant.

This is how carbon dating works: Carbon is a naturally abundant element found in the atmosphere, in the earth, in the oceans, and in every living creature.

C-12 is by far the most common isotope, while only about one in a trillion carbon atoms is C-14.

In living organisms, which are always taking in carbon, the levels of carbon 14 likewise stay constant.

But in a dead organism, no new carbon is coming in, and its carbon 14 gradually begins to decay.

It is naturally unstable and so it will spontaneously decay back into N-14 after a period of time.

It takes about 5,730 years for half of a sample of radiocarbon to decay back into nitrogen.

Back in the 1940s, the American chemist Willard Libby used this fact to determine the ages of organisms long dead.

Most carbon atoms have six protons and six neutrons in their nuclei and are called carbon 12. But a tiny percentage of carbon is made of carbon 14, or radiocarbon, which has six protons and eight neutrons and is not stable: half of any sample of it decays into other atoms after 5,700 years.

Before we come to the Carbon cycle, we have to understand why Carbon is so important in the first place. So, all of us have to depend on plants for our nutrition and survival, and plants, in turn, require Carbon-dioxide along with sunlight, to make their own nutrition.