Explain how radioactive dating works

01 Feb

There are two basic approaches: relative age dating, and absolute age dating.

What’s more, if the whole rock is badly weathered, it will be hard to find an intact mineral grain containing radioactive isotopes.

You might have noticed that many of the oldest age dates come from a mineral called zircon.

Chart of a few different isotope half lifes: In reality, geologists tend to mix and match relative and absolute age dates to piece together a geologic history.

If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric (absolute) age dating as well.

It’s based either on fossils which are recognized to represent a particular interval of time, or on radioactive decay of specific isotopes. Based on the Rule of Superposition, certain organisms clearly lived before others, during certain geologic times.

After all, a dinosaur wouldn’t be caught dead next to a trilobite.

I also like this simple exercise, a spin-off from an activity described on the USGS site above.

Take students on a neighborhood walk and see what you can observe about age dates around you.

Like the other kind of dating, geologic dating isn’t always simple.

Activity: Further discussion: Good overview as relates to the Grand Canyon: age dating: Use with this cross section of the Grand Canyon from the USGS’s teaching page: Canyon Have students reconstruct a simple geologic history — which are the oldest rocks shown? Are there any that you can’t tell using the Rule of Superposition?

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.