A New Leap Forward for Radiocarbon Dating
Until 1949, when archaeologists dug up prehistoric bones, stone points, charcoal remnants or other artifacts from early human history, they had no way of knowing exactly how old these objects were. Chemist Willard Libby changed that, devising an ingenious method for dating ancient objects based on the types of carbon atoms contained within them.
Libby and his colleagues based their idea on the fact that living things incorporate tiny amounts of a certain isotope of carbon (C-14) from the atmosphere into their structure; when they die, they stop adding new C-14, and the quantity left inside slowly degrades into a different element, nitrogen-14. By figuring out that the half-life of C-14 (the amount of time it takes for half of a given quantity of C-14 to decay into N-14) is 5,730 years, they could chemically analyze the ratio of C-14 to N-14 inside a piece of wood or bone and determine just how long it had been dead.
This technique has revolutionized archaeology, anthropology and other fields, allowing us to determine the absolute age of objects up to around 60,000 years old. All along, though, the precision of this technique has been limited by the fact that the amount of C-14 in the atmosphere has varied over time—and there has never been a great record of just how much it has fluctuated over the years.
With this in mind, a team of scientists from the University of Oxford and elsewhere was particularly excited when they excavated fossilized leaves and cores of sediment layers from beneath Japan’s Lake Suigetsu. These samples might not look like much, but because of the sediment’s unique layering and pristine condition, the find constitutes an unprecedented comprehensive record of atmospheric C-14 from roughly 11,200 to 52,800 years ago. The samples of sediment from this one location on the earth’s surface, in other words, will make our ability to date ancient artifacts found anywhere on the planet significantly more precise.