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Discuss the differences between relative methods of dating and absolute methods of dating. Provide two examples of the use of a relative dating technique and two examples of the use of an absolute dating technique for addressing research questions about human evolution?

• Geologists often need to know the age of material that they find. They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years. This is different to relative dating, which only puts geological events in time order.
• Relative age is the age of a rock layer (or the fossils it contains) compared to other layers. It can be determined by looking at the position of rock layers. Absolute age is the numeric age of a layer of rocks or fossils. Absolute age can be determined by using radiometric dating.
• Relative dating methods:-
• Law of superposition: This is one of the most basic techniques of relative dating geologists use. This principle says that the oldest rock layer is always on the bottom and layers above it get progressively younger. To understand this better, consider a four-layer cake.
• The oldest layer would be the bottom layer. It wouldn’t be possible for the other layers to be added without the bottom layer first. This same process applies with each layer to the cake added. You can’t start with the top layer and add the ones under it since there would be nothing to build on
• Principle of cross-cutting relations: The principle is another example of which came first. Instead of using layers, it involves features that cut through the rock, like a fault or a dike. In this case, the principle states that the item doing the cutting is younger than what is being cut. If we return to our example of the layered cake, the cake has to be there first before you can cut with a knife.
• The main relative dating method is stratigraphy, which is the study of layers of rocks or the objects embedded within those layers. This method is based on the assumption (which nearly always holds true) that deeper layers of rock were deposited earlier in Earth’s history, and thus are older than more shallow layers. The successive layers of rock represent successive intervals of time.
• Absolute Dating Examples:-
• i. Dendrochronology (used to date burials)
• ii. Radiocarbon dating (used to date the dead bodies)
• iii. Thermoluminescence (used to date ceramics)
• iv. Optically Stimulated Luminescence (used to date quartz)
• The most widely used and accepted form of absolute dating is radioactive decay dating
• Radioactive decay refers to the process in which a radioactive form of an element is converted into a nonradioactive product at a regular rate. The nucleus of every radioactive element (such as radium and uranium) spontaneously disintegrates over time, transforming itself into the nucleus of an atom of a different element. In the process of disintegration, the atom gives off radiation (energy emitted in the form of waves).
• Hence the term radioactive decay. Each element decays at its own rate, unaffected by external physical conditions. By measuring the amount of original and transformed atoms in an object, scientists can determine the age of that object.