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Relative rock dating worksheet

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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.

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Take students on a neighborhood walk and see what you can observe about age dates around you.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.For example, which is older, the bricks in a building or the building itself?Are there repairs or cracks in the sidewalk that came after the sidewalk was built?If they are folded into a syncline (a U-shaped fold) the youngest rocks are in the core of the fold.

The opposite is true for an anticline (a big dome-shaped fold).

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.

Relative age dating also means paying attention to crosscutting relationships.

Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.

Sedimentary rocks that contain fragments of another rock are younger than the rocks that the fragments came from.