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August 29, 2016

It’s not just teens that like to rebel; sometimes it’s rock layers like this EarthWord!

EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

Image shows the Colorado River cutting through the Grand Canyon
A view of the Grand Canyon, with the Great Unconformity visible. Credit: Alex Demas, USGS.Alex Demas, USGSPublic domain

The EarthWord: Unconformity


  • A geologic unconformity isn’t when a rock layer doesn’t follow the latest fashion trends, it’s when an older rock formation has been deformed or partially eroded before a younger rock layer, usually sedimentary, is laid down. That results in mismatched rock layers.


  • Unconformity comes from the Latin conformis, which meant “similar in shape.”

Use/Significance in the Earth Science Community:

  • Understanding unconformities, how they formed, and where they occur is an important part of learning the geologic history of a region. That, in turn, helps us understand potential mineral resources, potential geologic hazards, and even potential health effects of certain minerals.


  • USGS studies unconformities as part of our research into mineral resources, geologic hazards, and groundwater.

  • Also, the best name for a rock layer: The Great Unconformity. It’s one of the lowest layers in the Grand Canyon. And it’s also a great Indie Band name. That one’s on the house.

Next EarthWord: It’s not a radar for liars, it’s this week’s Earthword...

Hungry for some science, but you don’t have time for a full-course research plate? Then check out USGS Science Snippets, our snack-sized science series that focuses on the fun, weird, and fascinating stories of USGS science.

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