Wednesday, November 25, How do we determine numerical age of Earth? This situation changed with the discovery of radioactivity. In the s, geologists developed techniques for using measurements of radioactive elements to calculate the numerical ages of rocks. Geologists originally referred to these techniques as radiometric dating; more recently, this has come to be known as isotopic dating.
Geologic Age Dating Explained
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Introduction to Physical Geology Syllabus
The problem : By the mid 19th century it was obvious that Earth was much older than years, but how old? This problem attracted the attention of capable scholars but ultimately depended on serendipitous discoveries. Early attempts : Initially, three lines of evidence were pursued: Hutton attempted to estimate age based on the application of observed rates of sedimentation to the known thickness of the sedimentary rock column, achieving an approximation of 36 million years. This invoked three assumptions: Constant rates of sedimentation over time Thickness of newly deposited sediments similar to that of resulting sedimentary rocks There are no gaps or missing intervals in the rock record. In fact, each of these is a source of concern. The big problem is with the last assumption. The rock record preserves erosional surfaces that record intervals in which not only is deposition of sediment not occurring, but sediment that was already there who knows how much was removed.
Radiometric Age Dating
Radiometric dating calculates an age in years for geologic materials by measuring the presence of a short-life radioactive element, e. The term applies to all methods of age determination based on nuclear decay of naturally occurring radioactive isotopes. Bates and Jackson To determine the ages in years of Earth materials and the timing of geologic events such as exhumation and subduction, geologists utilize the process of radiometric decay. Geologists use these dates to further define the boundaries of the geologic periods shown on the geologic time scale.
Relative dating places rocks and events in sequence, i. The exact age of the object isn't known. With radiometric dating, an age of the object is calculated using the half-lives of radioactive elements to yield numerical dates.
