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.
Absolute Age
The absolute age of an Earth material is a measure of how old it actually is in years. With absolute age dating, you get a real age in actual years. Absolute age dating is like saying you are 13 years old and your grandfather is 77 years old. Since scientists work with many different types of Earth materials (rock, fossils, etc.), there are also many types of absolute age dating. Some types are useful in certain situations and for certain materials. 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.
Radiometric Dating
Radiometric dating (often called radioactive dating) is a way to find out how old something is. The method uses known decay rates. It is the most used method of to learn the age of rocks and other man-made or natural materials including the age of the Earth itself. Fossils may be dated by taking samples of rocks from above and below the fossil's original position.
It is essential to have as much information as possible about the material being dated and to check for possible signs of alteration. Measurements must be taken on samples from different parts of the rock. Different dating methods are also needed to confirm the age of a sample. For example, a study of the Amitsoq gneisses from western Greenland used five different radiometric dating methods to examine twelve samples and got agreement to within 30 million years on an age of 3,640 million years.
|
Radiometric dating methods are used to establish the geological time scale. Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead 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.
Video Guide:
|
|
Topic Tips
- Absolute age attempts to determine the exact age of something.
- There are many different techniques for determining the absolute age of rocks or fossils.