Last Updated on March 6, 2023 by admin
So, how exactly can we determine the age of a fossil? Absolute dating and relative dating are the two primary approaches that are used in the process of determining the age of a fossil. Using relative dating, one can estimate how old a fossil is by two truths and a lie for dating comparing it to rocks and fossils of the same type that have already been dated and having their dates determined. Absolute dating is a method that uses radiometric dating to determine the age of a fossil by measuring the rate of decay of isotopes. This can be done either within the fossil itself or, more commonly, within the rocks that are associated with it.
The Dating of Relatives
The relative dating methods are used to determine the ages of fossils the vast majority of the time. When using relative dating, the age of the fossil is determined by comparing it to something else whose age is previously established.
Take, for instance, the case where you possess a fossil trilobite and know that it was discovered in the Wheeler Formation. Since the age of the Wheeler Formation was determined to be close to 507 million years in the past, we can deduce that the age of the trilobite is also close to 507 million years. But if a rock formation has never been dated before, how can we know how long ago it was formed?
For the purpose of relative dating, also known as correlation, scientists can find particular kinds of fossils, which are referred to as index fossils. Index fossils are fossils that are known to only occur within a very particular age range. Index fossils can be used to determine the ages of other fossils. Index fossils are ideally suited to be made out of commonly found fossils that once inhabited a wide range of geographic areas. Some examples of such fossils include brachiopods, trilobites, and ammonites. If the fossil you are attempting to date is found in the same location as one of these index fossils, then the age of the fossil you are attempting to date must be within the age range of the index fossil.
There are situations when more than one index fossil is required. In this made-up scenario, a certain sort of brachiopod that is only known to have existed between 410 and 420 million years ago can be found fossilized within a rock formation. In addition, this rock formation holds an example of a species of trilobite that was thought to have been extinct between 415 and 425 million years ago. Because the rock formation contains both types of fossils, the age of the rock formation must fall within the range of dates that overlap, which is between 415 and 420 million years ago.
Researching the different layers of rock, often known as strata, can also be beneficial. Rock is formed by the deposition of successive layers. If the layer of rock that contains the fossil is higher up in the sequence than another layer, you can deduce that the older layers must be below the layer that contains the fossil. If it is located lower in the sequence, then it is of a more recent age. The fact that geological processes can create faulting and tilting of rocks can frequently make this situation more difficult to deal with.
Absolute dating is a process that utilizes radiometric dating techniques to establish the exact age of an object, such as a rock or fossil. This technique employs radioactive materials, which are naturally present in rocks and fossils, to create an almost exact replica of a geological clock. In many cases, dating fossils or the sedimentary rocks that the fossils are found in can be significantly more difficult than dating volcanic rocks. Therefore, in order to provide a date range for the rocks that contain fossils, it is often possible to date the layers of volcanic rock that are located above and below the layers that contain fossils.
Isotopes are the names given to the various configurations that certain chemical elements’ atoms can take. Through the process of radioactive decay, these isotopes degrade at a steady rate over the course of time. It is possible to determine the age of something by calculating the ratio of the amount of the original (parent) isotope to the amount of the daughter isotopes that it breaks down into.
The rate of this radioactive decay is measured in terms of its half-lives. If a radioactive isotope is said to have a half-life of 5,000 years, this indicates that after that amount of time, exactly half of the parent isotope will have decayed into the daughter isotopes. Then, after a further 5,000 years, fifty percent of the parent isotope that is still present will have decayed.
People are most familiar with carbon dating, but carbon dating is only occasionally useful for determining the age of fossils. The radioactive isotope of carbon known as carbon-14, which is used in carbon dating, has a half-life of 5730 years, which means that it degrades too quickly. It is only possible to use it to date fossils that are about 75,000 years old or less. The half-life of potassium-40, on the other hand, is approximately 1.25 billion years, and it is frequently found in rocks and minerals. As a result, it is an excellent method for determining the ages of fossils and rocks that are much older.
