Archaeology Fieldwork

Can ancient artifacts be dated by isotopes besides carbon-14?
Answered by Curiosity
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  1. Yes, there are other isotopes used to date ancient objects. Carbon-14 has a half-life of 5,700 years, making it effective for dating artifacts only up to about 60,000 years old. But other radioactive isotopes -- potassium-40, uranium-235, uranium-238, thorium-232 and rubidium-87 -- also can be found in the human body. They're called radioactive isotopes because they are unstable parts of elements. All of the isotopes mentioned above have half-lives of at least 700 million years. None of the isotopes may work for dating of anything that dies after the 1940s; use of nuclear bombs, reactors and open-air tests are making dating less precise.

    In 2010, scientists also announced a new way to use carbon-14 without having to destroy the artifact in any way. One of the problems with using radiocarbon dating is that it works by removing and burning a small sample of material from the object to determine its carbon-14 content. This helps to estimate the age of objects back about 45,000 to 60,000 years [source: Science Daily]. The new radiocarbon dating method uses plasma, or a gas that has been electrically charged, to oxidize the artifact's surface instead of applying an acid that burns the sample. In the new method, the entire object is placed in a special chamber with the plasma. The process occurs slowly and without damging the surface of objects.

    Argon dating was used by scientists to date fossils of several animal and hominid remains found in Ethiopia in 1997. The finds were estimated to be between 154,000 and 160,000 years old -- too old for carbon-14 dating to work [source: Zielinski]. Argon isn't normally found in nature, but it's simple to measure and results from decayed potassium-40 in volcanic rock. Scientists have found that they can irradiate rock samples to speed up the potassium-to-argon conversion and more precisely date very old rock samples. They couldn't rely on argon to date the hominid skulls, but they could date the rock imbedded in the sandstone near the hominid fossils. This indirect dating led to confirming that the find included the oldest known Homo sapien skulls.

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