In order to determine the arrangements or date of a series of events that occurred on the surface of the earth in the past. There are different methods are used to determine the date of different events that already occurred on the earth’s surface.
Types of Geological dating:
Generally, there are two types of geological dating.
- Relative dating
- Absolute dating
Relative geological dating:
In this type of dating, we can only determine the relative age of one rock formation or event with other. In other words, we can only determine that one rock formation or event is older or younger than the other. But we don’t know the exact age of that event or rock formation.
In relative dating there are different methods and tools are used, such as the law of superposition, index fossils, correlation of layers and rocks. Relative dating is all about putting the events and rock formations in a series and then comparing and determining which events occur before and after. But in the relative dating, we do not determine the actual age of rock formation and even we don’t have any clue of it.
But there are different methods used to make relative dating more accurate. Normally four different laws of stratigraphic are used for relative dating.
Nicholas steno proposed laws of stratigraphy, which are following:
- Law of superposition.
- Law of original horizontality.
- Law of original lateral continuity.
- Law of intrusion
- Law of cross-cutting.
Absolute dating:
Absolute geological dating is used to determine the exact time period of occurring of certain event or rock formation. Absolute geological dating is done by radioactive dating. Some rocks contain a certain amount of radioactive minerals. These radioactive minerals decay with the passage of time at a steady rate.
For radioactive dating, certain types of radioactive minerals have been used because not all types of elements are used for radioactive geological dating.
Here are some examples of radioactive elements that are used for absolute geological dating:
- Uranium (U-238)
- Potassium (K-40)
- Carbon (C-14)
- Samarium (sm-147)
- Rubidium (Rb-87)
- Thorium (Th-232)
- Uranium (U-235)
Among all above mentioned radioactive elements, Uranium (U-238) is an element that has a lot of importance for geological dating. For the absolute geological dating mostly the decaying scheme of U-238 is examined.
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