How can organic remains be dated

It's wasn't so long ago that megafauna ruled the American continent. Sloths and wooly mammoths pushed their weight around; horses and camels had their day. But after the end of the last Ice Age those animals disappeared, so when scientists turn up traces of those animals on archaeological remains, those remains go way back.

Last year, the University of Colorado's Doug Bamforth analyzed a cache of plus tools that a Boulder, Colorado, man accidentally unearthed in his yard. Those tools showed protein residue from camels and horses, so Bamforth dated them to the Clovis people who lived around about 13, years ago.

Not all scientists accept the accuracy of these tests, but that's nothing new in archaeology. Medieval manuscripts have a lot more to say than simply the words on their pages; often they're written on parchment made from animal skins, and organic material keeps its secrets for a long time.

Literary historian Timothy Stinson developed a way to extract the DNA from parchment itself, and if you can tell what animal a parchment was derived from, you might be able to tell more about what time and place the document originated.

Moa, the giant flightless birds of New Zealand, may have been extinct for at least years, but their dung is surprisingly resilient. On cave floors and buried in shelters, researchers found dung from the moa, with some of the samples being 15 cm nearly six inches in length.

The contents of the droppings give more than a window into the giant bird's eating habits—they preserve a record of what the long-gone moa's ecosystem was like.

The arid conditions of New Zealand caves provide the perfect place for poo preservation. Australia should, too, the researchers say, but the droppings of ancient marsupials just haven't turned up. As professor Alan Cooper says, "A key question for us is 'where has all the Australian poo gone?

If you think your metal detector has uncovered some treasures, try finding vintage plutonium in the backyard. Jon Schwantes of the Pacific Northwest National Laboratory was called in to analyze a sample of plutonium accidentally discovered in a safe during the cleanup of the Hanford nuclear site in Washington.

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After it forms high up in the atmosphere, plants breathe it in and animals breathe it out, said Thomas Higham, an archaeologist and radiocarbon dating specialist at the University of Oxford in England. Related: What's the oldest living thing alive today? While the most common form of carbon has six neutrons, carbon has two extra. That makes the isotope heavier and much less stable than the most common carbon form. So after thousands of years, carbon eventually breaks down. One of its neutrons splits into a proton and an electron.

While the electron escapes, the proton remains part of the atom. With one less neutron and one more proton, the isotope decays into nitrogen. When living things die, they stop taking in carbon and the amount that's left in their body starts the slow process of radioactive decay. Scientists know how long it takes for half of a given quantity of carbon to decay — a length of time called a half-life.

Alone, or in concert, these factors can lead to inaccuracies and misinterpretations by archaeologists without proper investigation of the potential problems associated with sampling and dating. To help resolve these issues, radiocarbon laboratories have conducted inter-laboratory comparison exercises see for example, the August special issue of Radiocarbon , devised rigorous pretreatment procedures to remove any carbon-containing compounds unrelated to the actual sample being dated, and developed calibration methods for terrestrial and marine carbon.

Radiocarbon dating can be used on either organic or inorganic carbonate materials. However, the most common materials dated by archaeologists are wood charcoal, shell, and bone. In brief, radiocarbon dating measures the amount of radioactive carbon 14 14C in a sample. When a biological organism dies, the radioactive carbon in its body begins to break down or decay. This process of decay occurs at a regular rate and can be measured.