Is a process of establishing the age of an object, such as a fossil or rock layer, by determining the number of years that is exsisted

 Radioactive isotopes tend to break down into stable isotopes of other elements in a process Radioactive Decay  Because radioactive decay occurs at a steady pace, scientists can use the relative amounts of stable and unstable isotopes present in an object to determine object’s age.

 Determining the absolute age of sample based on the ratio of parent material to daughter material  Half-Life is the time it takes for one-half of a radioactive sample to decay

 Uranium-Lead Method  Potassium-Argon Method  Carbon-14 Method

 Uranium-238 method is used for dating rocks back more than 10million years ago  Potassium -40 method is used to date rocks older than 100,000 year ago  Carbon-14 method is used mainly to date rocks that have lived within the last 50,000 years.

 A fossil is any naturally preserved evidence of life.

 In Rock  Mineral Replacement 1. Permineralization is a process in which minerals fill in pore spaces of an organism’s tissues. 2. Petrification of an of organisms, occurs when the oraganisms tissues are completely replaced by minerals Fossils in Amber(tree sap) Mummification When organisms die and dry out they are protected from bacteria because of the lack of water Frozen Fossils Fossils in Tar 1. One such place is the La Brea tar pits,in Los Angeles County, California. These tar pits were present 40,00o years ago

 Trace fossil are any naturally preserved evidence of an animal’s activity  Coprolites are preserved feces, or dung from, from animals  Mold is a cavity in the ground or orck ehere a plant or animal was buried.  Cast is an object created when sediment fills a mold and becomes rock

 Environmental Changes 1. Ex. By studying coral-reef fossils and applying the principle of uniformitarianism, they have determined that Iowa was once covered by a shallow sea.  Species existence on Earth 1. We know that fish existed before amphibians because fish were found in a lower layer of rock. In the same way, we know that amphibians existed before reptiles

 Index fossils are fossils of organisms that lived during a relatively short, well-defined time span.  Ex. Tropites, a genus of ammonites, existed for only about 2o million years, which makes it a good index fossils.  Where geologists find them in a rock layer, they know that the rock layer is between 208 million and 230 million years ago