Two Sides of Time: The Basics of Relative and Absolute Time
There are many ways that people can look at time, but the two major classifications that time tends to be grouped under are relative time and absolute time. The main difference between the two is numbers. When categorizing time as relative, there is no use for numbers: there are no dates or quantitative measurements for the passage of relative time. Relative time, also known as chronostratic time, is determined by looking at its relationship to other events. It is usually measured relative to other known events.
Absolute time on the other hand, is its mirror image since it is based entirely on numbers. Absolute time, also known as chronometric time, is usually measured in years, though it can be based on measurements using a combination of time units.
For instance, let's say you wanted to know the age of a fossil. If we knew the age of the rock the fossil was found in, we could determine the age of the fossil, relative to the age of the rock. This is one example of relative time. If we take this example a little bit further, you might qualify the age of the rock the fossil was discovered in based on where the rock was found, since sedimentary rocks are usually deposited in horizontal layers. Since each layer of sediment represents a period in time, you can date the rock relative to its sedimentary layer and classify its age relative to a period in time such as the Mesozoic or the Paleozoic eras. This is an example of relative time since its age is stated relative to some stratification layer or period in time rather than some definite numeric value or year.
On the other hand, you could carbon date the specimen and come up with an exact age, say 15,000 years old. This is an example of absolute time since you will quantify the age with some specific number.
Scientists use both forms of time measurement in their work today, choosing one over the other whenever it suits their purpose better. Einstein brought new ideas to the field of time physics when he began to categorize time as relative in his theory of relativity. Both are equally important parts of the geological time scale, and thus are important factors in geological dating.
Reference
- “Geological Time Scale.” 7 Jan. 2007.