The dates in this feature are provided in calendar years,
but are based on radiocarbon dating technology. Radiocarbon dating
has revolutionized archeology, but discrepancies can occur when
calendar dates and radiocarbon dates are compared. The farther
we go back in time, the harder it is to say that a calendar date
is the same as a radiocarbon date.
Calendar time refers to measured years before the present
- one revolution of the earth around the sun equals one year.
Radiocarbon years are based on the rate at which the carbon 14
isotope decays. Living things, such as seeds, plants, and bone,
absorb carbon 14 from the atmosphere. When organisms die, absorption stops and the C14 begins to decay at a constant rate. Archeologists estimate when the living material died by measuring the amount of C14 remaining.
Radiocarbon dates are calibrated because there is progressively
less agreement between them and calendar dates as we
go back in time. A calendar date of 10,000 years before present
is just that. A radiocarbon date of 10,000 years before present
is actually about 11,450 calendar years ago.