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How To Date A Dinosaur Fossil
When paleontologist Mary Schweitzer found soft tissue in a Tyrannosaurus rex fossil , her discovery raised an obvious question -- how the tissue could have survived so long? The bone was 68 million years old, and conventional wisdom about fossilization is that all soft tissue, from blood to brains , decomposes. Only hard parts, like bones and teeth, can become fossils. But for some people, the discovery raised a different question. How do scientists know the bones are really 68 million years old? Today's knowledge of fossil ages comes primarily from radiometric dating , also known as radioactive dating. Radiometric dating relies on the properties of isotopes. These are chemical elements, like carbon or uranium, that are identical except for one key feature -- the number of neutrons in their nucleus. Atoms may have an equal number of protons and neutrons. If, however, there are too many or too few neutrons, the atom is unstable, and it sheds particles until its nucleus reaches a stable state.
The most widely known form of radiometric dating is carbon dating. This is what archaeologists use to determine the age of human-made artifacts. But carbon dating won't work on dinosaur bones. The half-life of carbon is only 5, years, so carbon dating is only effective on samples that are less than 50, years old. Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old. To determine the ages of these specimens, scientists need an isotope with a very long half-life. Some of the isotopes used for this purpose are uranium, uranium and potassium , each of which has a half-life of more than a million years.
Creationists bring up Carbon 14 dating of dinosaur bones all the time. This shows a lack of basic understanding of how the method is used and what material it can be used to date. Carbon 14 is used to date things that were once living and in equilibrium with the atmosphere. This neutron bombardment produces the radioactive isotope carbon The radioactive carbon combines with oxygen to form carbon dioxide and is incorporated into the cycle of living things.