Wikipedia:Today's featured article/July 6, 2023
Radiocarbon dating is used to determine the age of carbon-bearing material by measuring its levels of radiocarbon, the radioactive isotope carbon-14. Invented by Willard Libby in the late 1940s, it soon became a standard tool for archaeologists. Radiocarbon is constantly created in the atmosphere, when cosmic rays create free neutrons that hit nitrogen. Plants take in radiocarbon through photosynthesis, and animals eat the plants. After death, they stop exchanging carbon with the environment. Half of the radiocarbon decays every 5,730 years; the oldest dates that can be reliably estimated are around 50,000 years ago. The amount of radiocarbon in the atmosphere was reduced starting from the late 19th century by fossil fuels, which contain little radiocarbon, but nuclear weapons testing almost doubled levels by around 1965. Accelerator mass spectrometry (apparatus pictured) is the standard method used, which allows minute samples. Libby received the Nobel Prize in Chemistry in 1960. (Full article...)