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Relative dating of rocks and events

Biostratigraphy: One of the first and most basic scientific dating methods is also one of the easiest to understand.Layers of rock build one atop another — find a fossil or artifact in one layer, and you can reasonably assume it’s older than anything above it.The uranium-thorium method is often helpful for dating finds in the 40,000- to 500,000-year-old range, too old for radiocarbon but too young for K-Ar or Ar-Ar.Over time, certain kinds of rocks and organic material, such as coral and teeth, are very good at trapping electrons from sunlight and cosmic rays pummeling Earth.Unlike observation-based relative dating, most absolute methods require some of the find to be destroyed by heat or other means.This family of dating methods, some more than a century old, takes advantage of the environment’s natural radioactivity.

The good dates are confirmed using at least two different methods, ideally involving multiple independent labs for each method to cross-check results.Both plants and animals exchange carbon with their environment until they die.Afterward, the amount of the radioactive isotope carbon-14 in their remains decreases.Sometimes only one method is possible, reducing the confidence researchers have in the results. “They’re based on ‘it’s that old because I say so,’ a popular approach by some of my older colleagues,” says Shea, laughing, “though I find I like it myself as I get more gray hair.” Kidding aside, dating a find is crucial for understanding its significance and relation to other fossils or artifacts.Methods fall into one of two categories: relative or absolute.Egyptologists, for example, created a relative chronology of pre-pharaonic Egypt based on increasing complexity in ceramics found at burial sites.Whenever possible, researchers use one or more absolute dating methods, which provide an age for the actual fossil or artifact.This includes factoring in many variables, such as the amount of radiation the object was exposed to each year.These techniques are accurate only for material ranging from a few thousand to 500,000 years old — some researchers argue the accuracy diminishes significantly after 100,000 years.Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.A submethod within biostratigraphy is faunal association: Sometimes researchers can determine a rough age for a fossil based on established ages of other fauna from the same layer — especially microfauna, which evolve faster, creating shorter spans in the fossil record for each species.

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  1. Creationists have long insisted that the main evidence for evolution — the fossil record — involves a serious case of circular reasoning. That is, the fossil evidence that life has evolved from simple to complex forms over the geological ages depends on the geological ages of the specific rocks in which these fossils are found.

  2. This dating scene is dead. Everything Worth Knowing About. Scientific Dating Methods This dating scene is dead.

  3. Learn how scientists determine the ages of rocks and fossils. We'll explore both relative and numerical dating on our quest to understand the.

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