Age of Rocks and Fossils (Part 2)

• Fossils are remains or traces of organisms that have been preserved.

• They are commonly found in sedimentary rocks.

• Index fossils can be used for dating.

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Using Fossils for Dating

• Fossils of organisms that lived during very specific times in history

• If a new fossil is found near an index fossil, it is probably from the same time period.

• They fossils can help date organisms and rock layers.

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Index Fossils

Relative dating, including the use of index fossils, is used in combination with other methods to provide a more complete picture of the history of an area.

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• Uses various techniques to determine the exact age of rocks and fossils

• It requires special equipment and expertise, but is the most accurate method.

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Absolute Dating

Radioactive (Radiometric) Dating

• Calculated based on the amounts of certain radioactive substances

• This method measures the amount of radioactive element present in the rock sample. It compares it to the rate the isotopes of that element decay.

• A half-life is the time it takes for half of the atoms in a sample to decay.

• Radioactive isotopes decay at predictable rates.

  • Carbon-14 (5,730 years)

  • Uranium-235 (704 million years)

• Measures the original isotopes to the decay products to calculate age.

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Radioactive Isotopes

• Involves counting rings on tree trunks

• Based on the fact that trees add one growth ring per year

• Characteristics and width of rings can shed light on environmental and climate conditions

• Used to date wood samples with high precision
  

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Dendrochronology

Some objects, such as petrified wood, need multiple dating methods. Scientists may use radiometric dating and dendrochronology to determine age.

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