C14, also known as carbon-14, is a radioactive isotope of carbon. It is formed in the atmosphere when cosmic rays interact with nitrogen-14. C14 is present in trace amounts in the environment and is absorbed by living organisms through processes like photosynthesis and respiration. When an organism dies, it stops taking in C14, and the isotope begins to decay at a known rate, called its half-life, which is about 5,730 years. This property makes C14 useful for dating ancient organic materials, a method known as radiocarbon dating. This technique helps archaeologists and scientists determine the age of artifacts and fossils.