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?
All absolute isotopic ages are based on radioactive decay , a process whereby a specific atom or isotope is converted into another specific atom or isotope at a constant and known rate. Most elements exist in different atomic forms that are identical in their chemical properties but differ in the number of neutral particles—i. For a single element, these atoms are called isotopes. Because isotopes differ in mass , their relative abundance can be determined if the masses are separated in a mass spectrometer see below Use of mass spectrometers. Radioactive decay can be observed in the laboratory by either of two means: 1 a radiation counter e.
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The aging process in human beings is easy to see. As we age, our hair turns gray, our skin wrinkles etc. However, rocks and other objects in nature do not give off such obvious clues about how long they have been around. Radiometric dating is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes. Different methods of radiometric dating can be used to estimate the age of a variety of natural and even man-made materials.