Radiometric Dating


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By Eugene Alvin Villar (seav) – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=4627839

Radiometric Dating (Campbell Biology)

Researchers measure radioactive decay in fossils to date these relics of past life. Fossils provide a large body of evidence for evolution, documenting differences between organisms from the past and those living at present and giving us insight into species that have disappeared over time. While the layering of fossil beds establishes that deeper fossils are older than more shallow ones, the actual age (in years) of the fossils in each layer cannot be determined by position alone. This is where radioactive isotopes come in. A “parent” isotope decays into its “daughter” isotope at a fixed rate, expressed as the half-life of the isotope—the time it takes for 50% of the parent isotope to decay. Each radioactive isotope has a characteristic half-life that is not affected by temperature, pressure, or any other environmental variable. Using a process called radiometric dating, scientists measure the ratio of different isotopes and calculate how many half-lives (in years) have passed since an organism was fossilized or a rock was formed. Half-life values range from very short for some isotopes, measured in seconds or days, to extremely long—uranium-238 has a half-life of 4.5 billion years! Each isotope can best “measure” a particular range of years: Uranium-238 was used to determine that moon rocks are approximately 4.5 billion years old, similar to the estimated age of Earth.

Source:

Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html

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