All living things ingest the element carbon in the form of its isotope carbon 14 (14C), which floats freely in the atmosphere and is present in all foods. When a life form stops ingesting 14C (when it, you know, dies), no new 14C enters the body, and the 14C in the body begins to radioactively decay into 14N (nitrogen isotope 14). Importantly, 14C decays into 14N at a known and pretty stable rate: After about 5,600 years, only half of the original 14C remains because the rest has decayed into 14N.According to the passage, scientists can observe radioactive decay to determine