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.A shell is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, as from aragonite to calcite. Adpression (compression-impression) Compression Fossils, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism’s tissues.Absolute Dating Methods Cation-Ratio Dating – used to date rock surfaces such as stone artifacts and cliff and ground drawings.
The more daughter material there is the older the rock is.*Thermoluminescence Dating – very useful for determining the age of pottery.Has the advantage of covering the time interval between radiocarbon and pottasium-argon dating or 40,000,000 years.If you know the rate of decay for a radioactive element in a rock you can figure out the absolute age of the rock.Half-life * the time needed for half of a sample of a radioactive substance to undergo radioactive decay.* 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.After every half-life, the amount of parent material decrease by one-half. Potassium-Argon Method * Potassium-40 has a half-life of 1.Types of Radiometric Dating Scientists use different radiometric-dating methods based on the estimated age of an object. 3 billion years, and it decays leaving a daughter material of argon.* 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.