Relative versus absolute dating
Unlike people, you can’t really guess the age of a rock from looking at it.Yet, you’ve heard the news: Earth is 4.6 billion years old. That corn cob found in an ancient Native American fire pit is 1,000 years old. Geologic age dating—assigning an age to materials—is an entire discipline of its own.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.In a way this field, called geochronology, is some of the purest detective work earth scientists do.There are two basic approaches: relative age dating, and absolute age dating.Before the advent of absolute dating methods in the twentieth century, nearly all dating was relative.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.
Free 5-day trial You may not associate geology with time, but the former greatly depends on the latter.
In this lesson we'll discuss both absolute and relative time, and how they work together to give us a detailed history of Earth.
Here is an easy-to understand analogy for your students: relative age dating is like saying that your grandfather is older than you.
Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.