Carbon-14 is created 10 miles above Earth when cosmic rays strike the atmosphere.

Carbon-14 (14C) is a radioactive isotope of carbon that is constantly produced in the Earth's upper atmosphere, specifically at altitudes of 9 to 15 kilometers (about 6 to 10 miles). This process occurs when high-energy cosmic rays from outer space collide with atmospheric atoms, releasing thermal neutrons. These neutrons then strike nitrogen-14 atoms, displacing a proton and turning the nitrogen into carbon-14.Once formed, carbon-14 combines with oxygen to create radioactive carbon dioxide, which is then absorbed by plants through photosynthesis. Animals and humans then consume these plants, ensuring that all living things maintain a concentration of carbon-14 that matches the atmospheric level. This cycle continues throughout the life of the organism, keeping the ratio of carbon-12 to carbon-14 stable.The breakthrough for using this phenomenon for dating was made by Willard Libby and his team at the University of Chicago in 1946. Libby discovered that carbon-14 has a specific half-life of approximately 5,730 years. This means that every 5,730 years, half of the carbon-14 in a dead specimen will have decayed back into nitrogen-14.By measuring the ratio of carbon isotopes in organic remains, researchers can calculate the time elapsed since death with high precision. This method, known as radiocarbon dating, revolutionized archaeology and geology. For his pioneering work, Willard Libby was awarded the Nobel Prize in Chemistry in 1960.