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* This method is used mainly to date rocks older than 100,000 years.
* Relies on the fact that when volcanic rocks are heated to extremely high temperatures, they release any argon trapped in them. Uranium-Lead Method * Uranium-238 is a radioactive isotope with a half-life of 4. Uranium-238 decays in a series of steps to lead-206.
a disadvantage to this technique is that in order to get accurate results, the sediment to be tested cannot be exposed to light, making sampling difficult.
Radiometric Dating Determining the absolute age of a sample, based on the ratio of parent material to daughter material.
* Living plants and animals contain a constant ratio of carbon-14 to carbon-12. Once a plant or animal dies, no new carbon is taken in. The amount of carbon-14 begins to decrease as the plant or animal decays. – Radiocarbon (14C) is a radioactive form of the element carbon. Fossils: evidence of past life Fossils are the preserved remains or traces of animals (also known aszoolites), plants, and other organisms from the remote past.An endocast or internal mold is formed when sediments or minerals fill the internal cavity of an organism. Authigenic mineralisation This is a special form of cast and mold formation.he organism (or fragment of organism) can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it. Replacement and recrystallization Replacement occurs when the shell, bone or other tissue is replaced with another mineral.* To determine the absolute ages of fossils and rocks, * scientists analyze isotopes of radioactive elements.Isotopes * atoms of the same element that have the same number of protons but different numbers of neutrons. Radioactive decay * Radioactive isotopes tend to break down into stable isotopes of the same or other elements.