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A stable isotope of carbon, having six protons and six neutrons in the nucleus. Carbon-12 makes up most naturally occurring carbon.
References in periodicals archive ?
There's lighter carbon-12 in the atmosphere because the increase in atmospheric carbon levels is due entirely to humans burning fossil fuels.
SIMS analyzes the ratio of carbon-13 to carbon-12 isotopes, comparing samples from the alleged fossils with those from empty sections of rock.
In sediment records, when you look at the ratio of carbon-12 to carbon-13 in a particular species, you see that it's stable and then it abruptly shifts, wiggles back and forth and slowly returns to pre-event values over hundreds of thousands of years," Schaller said.
But the researchers used methanol ice that contained a variety of carbon known as carbon-13; any contaminants would have carried the slightly lighter carbon-12.
Isotopes are variants of the same chemical element with different atomic weights due to having different numbers of neutrons, such as the most common carbon isotope, carbon-12, and a heavier stable isotope, carbon-13.
The technique compares the amount of carbon-14 (C-14), a less common form of atmospheric carbon, to carbon-12 (C-12), which is more stable and abundant.
Carbon-14 is a heavier isotope of carbon than the 'regular' carbon-12 and, moreover, it is radioactive.
By analyzing the proportions of CO2 molecules containing the different carbon isotopes, scientists have found that the percentage of CO2 containing the Carbon-12 isotope is increasing.
Atomic weight is (according to Wikipedia) "the ratio of the average mass of atoms of an element (from a given source) to 1/12 of the mass of an atom of carbon-12.
Carbon-14, for example, is carbon with 14 neutrons and is an isotope of carbon-12, which has 12 neutrons.
There is a different ratio of carbon-14 and carbon-12 in steroid hormones made from plant sources compared with animal sources.