Science social sciences archaeology methodology dating
The radioactive carbon-14 method of dating is used to determine the age of organic matter that is several hundred years to approximately 50,000 years old.
Carbon dating is possible because all organic matter, including bones and other hard parts, contains carbon and thus contains a scalable proportion of carbon-14 to its decay product, nitrogen-14.
In dendrochronology, the age of wood can be determined through the counting of the number of annual rings in its cross section.
Tree ring growth reflects the rainfall conditions that prevailed during the years of the tree's life.
Since the rate of radioactive decay of any particular isotope is known, the age of a specimen can be computed from the relative proportions of the remaining radioactive material and its decay products.
By this method the age of the earth is estimated to be about 4.5 billion years old.
Fission track dating is based on the fact that when uranium-238 atoms fission within a solid medium such as a mineral or a glass, they expel charged particles that leave a trail of damage (known as fission tracks) preserved in the medium.
The number of tracks per unit area is a function of time and the uranium concentration.
The conventional method of measuring the amount of radioactive carbon-14 in a sample involved the detection of individual carbon-14 decay events. This technique involves the direct counting of carbon-14 atoms through the use of the accelerator mass spectrometer and has the advantage of being able to use sample sizes up to 1,000 times smaller than those used by conventional radiocarbon dating.Some of the radioactive elements used in dating and their decay products (their stable daughter isotopes) are uranium-238 to lead-206, uranium-235 to lead-207, uranium-234 to thorium-230, thorium-232 to lead-208, samarium-147 to neodymium-143, rubidium-87 to strontium-87, and potassium-40 to argon-40.Each radioactive member of these series has a known, constant decay rate, measured by its half-life , that is unaffected by any physical or chemical changes.The accelerator mass spectrometer technique reduces the amount of statistical error involved in the process of counting carbon-14 ions and therefore produces dates that have smaller standard errors than the conventional method.Paleomagnetic dating is based on changes in the orientation and intensity of the earth's magnetic field that have occurred over time.