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Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.
In contrast, methane made from petroleum products had no measurable radioactivity.
As the Earth's upper atmosphere is bombarded by cosmic radiation, atmospheric nitrogen is broken down into an unstable isotope of carbon - carbon 14 (C-14).
The unstable isotope is brought to Earth by atmospheric activity, such as storms, and becomes fixed in the biosphere.
This discovery meant that there are three naturally occurring isotopes of carbon: Whereas carbon-12 and carbon-13 are stable isotopes, carbon-14 is unstable or radioactive.
The C-14 within an organism is continually decaying into stable carbon isotopes, but since the organism is absorbing more C-14 during its life, the ratio of C-14 to C-12 remains about the same as the ratio in the atmosphere.
Recall that atoms are the basic building blocks of matter.
Atoms are made up of much smaller particles called protons, neutrons, and electrons.
Radiocarbon, or Carbon-14, dating is probably one of the most widely used and best known absolute dating methods. Radiocarbon dating relies on a simple natural phenomenon.
This allowed for the establishment of world-wide chronologies.
The ensuing atomic interactions create a steady supply of c14 that rapidly diffuses throughout the atmosphere.