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245

limestone

OLogy Series
geology
card
245

limestone

OLogy Series
geology

Limestone is made up of fossils. After small marine animals die, their shells and skeletons build up on the ocean floor. Over time, the layers of fragments press down on each other, squeeze out the water, and recrystallize into solid rock. Sometimes the original shells, which are now fossils, are still visible. These fossils give scientists important clues about ancient life.

Clues in the Limestone
What has limestone taught us about the Grand Canyon? More than you can imagine! The Grand Canyon has been formed by a river that exposed layers of sedimentary rock such as limestone, sandstone, and shale. These layers formed on top of each other over time, so they get older and older the lower they go. And since so many contain fossils and other clues of earlier times, the walls are like a history book that lets scientists look back in time. Limestone forms in the oceans. So how did it end up in the Grand Canyon? Because the location of the Grand Canyon was once covered by ocean. Scientists can determine when this happened by studying the different layers of limestone found in the lower, middle, and upper walls of the Grand Canyon.

Limestone forms in both freshwater and marine environments. The best way to determine the environment in which a limestone formed is by:

studying its fossils

tasting it to see if it tastes salty

holding it up to your ear to see if you hear the ocean

Are you right?

Correct!

Geologists can learn a lot about limestone by studying its fossils. If they know where and when the fossil animal lived, they can assume that the limestone formed in the same environment at about the same time.

Rondi Davies, Earth scientist

Limestone forms in warm, shallow oceans. So when we find limestone on a mountain or in a cold climate like Antarctica, we know that this part of the Earth has changed over time.

Limestone is only found in oceans.

Fact
or
Fiction
?

Fiction

Limestone is also found on land, giving geologists clues about where oceans once covered the Earth.

Most people have eaten limestone.

Fact
or
Fiction
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Fact

In fact, you may have eaten some today! Limestone is in the dust that covers chewing gum. It's also found in flour, tofu, and even toothpaste!

Definition: a rock that formed in shallow oceans from fragments of marine animals
Type: sedimentary
Appearance: typically light-colored or gray; may contain visible fossils
Primary mineral: calcite (the mineral found in shells)
Cool fact: Limestone is used to make toothpaste, cement, and even tofu.

Image credits: courtesy of AMNH; Rondi Davies: AMNH.