Relative dating and absolute dating of fossils

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This method is based on the assumption (which nearly always holds true) that deeper layers of rock were deposited earlier in Earth's history, and thus are older than more shallow layers.The successive layers of rock represent successive intervals of time.Before the advent of absolute dating methods in the twentieth century, nearly all dating was relative.The main relative dating method is stratigraphy (pronounced stra-TI-gra-fee), which is the study of layers of rocks or the objects embedded within those layers.Narrow rings grow in cold or dry years, and wide rings grow in warm or wet years.The rings form a distinctive pattern, which is the same for all members in a given species and geographical area.By measuring the amount of carbon-14 remaining, scientists can pinpoint the exact date of the organism's death.The range of conventional radiocarbon dating is 30,000 to 40,000 years.

In the process of disintegration, the atom gives off radiation (energy emitted in the form of waves). Each element decays at its own rate, unaffected by external physical conditions.The age of the remains of plants, animals, and other organic material can be determined by measuring the amount of carbon-14 contained in that material.Carbon-14, a radioactive form of the element carbon, is created in the atmosphere by cosmic rays (invisible, high-energy particles that constantly bombard Earth from all directions in space).Relative dating methods are used to determine only if one sample is older or younger than another.Absolute dating methods are used to determine an actual date in years for the age of an object.

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