Absolute Age: Definition & Dating

Instructor: Josh Corbat

Josh has taught Earth Science and Physical Science at the High School level and holds a Master of Education degree from UNC-Chapel Hill.

Imagine braving the desert heat for days or even weeks as you dig for dinosaur bones. You find something extraordinary and want to know as much about it as you can. In this lesson, you'll learn how scientists determine the absolute age of materials.

What is Absolute Age?

Scientists who study the ancient Earth have been working for hundreds of years to build an accurate timeline of the formation of the planet and the evolution of all life. This is no simple task! In order to build and improve this timeline, scientists must have several types of accurate methods they can use to determine the ages of materials.

There are two main categories by which they do this: relative age dating and absolute age dating. In relative age dating, scientists study a material and compare it to other similar materials in order to establish a timeline. It is essentially a big sequence: This comes first, that comes next, this comes last. This method is a bit vague, which is why modern scientists have developed many methods by which to determine the absolute age of Earth materials.

The absolute age of an Earth material is a measure of how old it actually is in years. Some scientists prefer to call it calendar age, because the term suggests that the age can be plotted on a calendar. The absolute age of a material is much more desirable when constructing the timeline of our planet because it does not rely on comparisons to other materials. Instead of saying a material is older or younger than something else, scientists can simply report the age in years. Imagine it this way: If you have any siblings, using relative age dating would be like saying, 'I am older than my brother but younger than my sister,' but using absolute age dating would be like saying, 'I am 23 years old.'

Types of Absolute Age Dating

Since scientists work with many different types of Earth materials (rock, fossils, etc.), there are many types of absolute age dating. Some types are useful in certain situations and for certain materials, while others are perfect for other jobs. For example, while one type of absolute age dating may be perfect to figure out how old a dinosaur bone fossil is, another method of dating might be perfect to figure out the age of a rock sample. Let's look at a few prominent types of absolute age dating.

Radiocarbon dating: Radiocarbon dating (also simply called carbon dating) is one of the most widely used and famous types of absolute age dating. This method of dating is useful for materials that were once living, but has a significant limitation: Carbon dating is only reliable for materials that are up to about 75,000 years old. If scientists encountered anything older than that, they would have to use a different method.

Potassium-argon dating: This type of dating is very similar to radiocarbon dating, in that is uses essentially the same methods. The upside of potassium-argon dating, though, is that much older samples can be tested. With potassium-argon dating, scientists can figure out the age of samples that are billions of years old.

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