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Geological strata dating

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.

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.

This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.

These use radioactive minerals in rocks as geological clocks.

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.

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.

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.

That’s because zircon is super tough – it resists weathering. Each radioactive isotope works best for particular applications.

The half-life of carbon 14, for example, is 5,730 years.

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