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The latter can create significant variations in The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere.
Atmospheric nuclear weapon tests almost doubled the concentration of The above-ground nuclear tests that occurred in several countries between 19 (see nuclear test list) dramatically increased the amount of carbon-14 in the atmosphere and subsequently in the biosphere; after the tests ended, the atmospheric concentration of the isotope began to decrease.
Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples.
Either interbreeding with Neanderthals or other populations led to the unusual genetic makeup, he said, or humans evolved far earlier than the extant fossil record suggests.
The results are published in the American Journal of Human Genetics.
C, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.
These are relatively low energies; the maximum distance traveled is estimated to be 22 cm in air and 0.27 mm in body tissue.
The fraction of the radiation transmitted through the dead skin layer is estimated to be 0.11.