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Relative age dating methods

The Wheeler Formation has been previously dated to approximately 507 million year old, so we know the trilobite is also about 507 million years old.But, how can we determine how old a rock formation is, if it hasn’t previously been dated?We define the rate of this radioactive decay in half-lives.

Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.

Index fossils are fossils that are known to only occur within a very specific age range.

Relative dating and radiometric dating are used to determine age of fossils and geologic features, but with different methods.

Relative dating uses observation of location within rock layers, while radiometric dating uses data from the decay of radioactive substances within an object.

Potassium-40 on the other hand has a half like of 1.25 billion years and is common in rocks and minerals.

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This makes it ideal for dating much older rocks and fossils.For example, carbon dating is used to determine the age of organic materials.Once something dies, it ceases taking in new carbon-14, and the existing carbon-14 within the organism decays into nitrogen at a fixed rate.Relative dating helps determine what came first and what followed, but doesn't help determine actual age.Radiometric dating, or numeric dating, determines an actual or approximate age of an object by studying the rate of decay of radioactive isotopes, such as uranium, potassium, rubidium and carbon-14 within that object. This rate provides scientists with an accurate measurement system to determine age.So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.The atoms in some chemical elements have different forms, called isotopes.These isotopes break down at a constant rate over time through radioactive decay.By measuring the ratio of the amount of the original (parent) isotope to the amount of the (daughter) isotopes that it breaks down into an age can be determined.Then after another 5,000 years half of the remaining parent isotope will have decayed.While people are most familiar with carbon dating, carbon dating is rarely applicable to fossils.

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