Use of radioactive isotopes in carbon dating
And because there's a constant quantity of C14 in the atmosphere, there's a constant, corresponding quantity of it in the bodies of all living things, at least while they're still alive. That doesn't mean it's dangerous, only that it's unstable. See, when an organism dies, it stops taking in carbon.
And the C14 in the organism's tissues starts to decay at a precise speed, but the amount of carbon-12 stays the same, since it's not radioactive.
C14 is a radioactive isotope that's made when cosmic rays bombard nitrogen atoms at high altitudes, converting them to this excited form.
When some living things, like plants and algae, make their own food through photosynthesis, they take in carbon dioxide from the air.
And radioisotope dating may be one of the more sophisticated methods we use to know the age of fossils, but it's not the only one.
The Earth is 4.54 billion years old; 3.8 billion years ago, the very first life form came into existence; 225 million years ago, dinosaurs came on the scene; and man took his first steps in Africa 200,000 years ago. Carbon-14 and other radioisotopes are used to measure the age of fossils, rocks, and other materials that make up Earth's geologic history. But at any given time, there are trace amounts of carbon-14, or C14, in the atmosphere.
And they contribute to the hundreds of lines of evidence supporting Charles Darwin's theory of evolution, which continues to stand the test of time. See, all living things contain carbon, which has six protons and six neutrons, so in its typical form, we call it carbon-12.