it decomposes or fossilizes. Plants take in carbon dioxide through photosynthesis and the carbon-14 makes its way up the food chain and into all living organisms. This technique works well for materials up to around 50,000 years old. Libby thus reasoned that by measuring carbon 14 levels in the remains of an organism that died long ago, one could estimate the time of its death. For the record, a beta-particle is a specific type of nuclear decay. Select a subject to preview related courses: Atmospheric carbon-14 rapidly reacts with oxygen in air to form carbon dioxide and enters the carbon cycle.