how are relative dating and absolute dating different

http://sciencelearn.org.nz/Contexts/Dating-the-Past/Science-Ideas-and-Concepts/Absolute-dating

Relative dating and absolute dating are two methods used by geologists and archaeologists to determine the age of rocks, fossils, and artifacts. The main difference between these two methods lies in their approach to determining age.

Relative dating involves determining the age of an object or event by comparing it to other objects or events. It relies on the principles of stratigraphy, which involve studying the layers of rock or soil to establish a sequence of events. By examining the position of an object or fossil within the layers, researchers can infer its relative age. This method does not provide an exact age, but it can help establish a chronological order.

To determine relative age using stratigraphy, scientists follow these steps:

1. Law of Superposition: This principle states that the older layers of rock or soil are found beneath younger layers. By examining the layers and their content, scientists can determine the relative age of the objects within them.

2. Principle of Original Horizontality: This principle suggests that sediments are originally deposited in horizontal layers. Deviations from horizontal layers indicate changes in the environment or the occurrence of geological events.

3. Principle of Cross-Cutting Relationships: This principle states that any geological feature that cuts across another layer or object is younger than the layer or object it cuts through. This helps scientists determine the relative age of different features.

Absolute dating, on the other hand, provides a specific numerical age for an object or event. It relies on various scientific techniques that measure the amount of certain isotopes or minerals present in a sample. These techniques include radiometric dating, dendrochronology, and thermoluminescence.

Here's a brief overview of some common absolute dating methods:

1. Radiometric Dating: This method uses the decay of radioactive isotopes in minerals to calculate the age of rocks or fossils. By measuring the ratio of parent isotopes to their decay products, scientists can determine the age of the sample.

2. Dendrochronology: Also known as tree-ring dating, dendrochronology involves analyzing the patterns of tree rings to determine the age of a wooden artifact or a fossil. Each annual growth ring represents one year of growth.

3. Thermoluminescence: This method determines the last time a crystal was heated or exposed to sunlight by measuring the amount of trapped electrons in the crystal lattice. It is often used to date artifacts made of fired clay or burned objects.

In summary, relative dating provides an estimation of age based on the relationship between objects or events, while absolute dating uses scientific techniques to provide a precise numerical age.