14c12c ratio carbon dating speed dating in manila philippines
Scientists now realize that production of carbon-14 has not been constant over the last 10,000 years, but has changed as the radiation from the sun has changed.
Carbon dates reported in the 1950s and 1960s should be questioned, because those studies were conducted before carbon dating was calibrated by comparision with other dating methods.
Both methods rely on the ongoing production of radiocarbon in the upper atmosphere.
However, the carbon-14 already in the organism's body continues to decay at a constant rate.
Therefore, the amount of carbon-14 in an artifact decreases at a predictable rate while the amount of carbon-12 remains constant.
Carbon-14 is created from nitrogen-14 in the upper atmosphere of the earth.
Radiation from the sun collides with atoms in the atmosphere.
This technique is not restricted to bones; it can also be used on cloth, wood and plant fibers. The short half-life of carbon-14 means its cannot be used to date extremely old fossils.