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.
We can compare the amount of radioactive elements in a rock to the amount of specific non-radioactive elements in a rock, do some math and determine how old the rock is. So, if we find a rock that has uranium in it, we can compare it to the amount of lead in the rock to find out how old the rock is.
If you have the right kind of rocks, this method is very accurate.
The narrower a range of time that an animal lived, the better it is as an index of a specific time.
Are there repairs or cracks in the sidewalk that came after the sidewalk was built?Look for “absolute” ages such as cornerstones, dates carved into fresh concrete, or dates stamped on manhole covers.Absolute age dating: Have students work alone or in pairs to find an article or paper that uses radiometric age dating.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.