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034

sedimentary rocks

OLogy Series
geology
card
034

sedimentary rocks

OLogy Series
geology

The next time you're at a beach, grab a handful of sand. This material is sediment. Sediment carried by water and wind is deposited in layers. When sediment becomes cemented together it forms sedimentary rocks. These rocks are the best places to search for fossils.

The Geology-Paleontology Connection
Geologists use a special technique called radiometric dating to figure out the age of different rocks. Once paleontologists know the age of a rock, they know the age of the fossils that are inside it. This helps create a timeline of when different dinosaurs lived. Because Pisanosaurus remains were found in much older rocks than T. rex remains, we know that Pisanosaurus lived before T. rex. Geologists have divided Earth's history into four major
eras. The Mesozoic (Meh-zuh-ZOH-ik) Era lasted from 248 million years ago to 65 million years ago. Today, we live in the Cenozoic (sen-oh-ZOH-ik) Era.

James Hutton, the First Rock Star
Before the mid-1700s, most scientists believed that rocks formed as a result of a great flood. James Hutton, a Scottish scientist who lived from 1726-1797 didn't agree. Instead, Hutton proposed the theory that rocks are slowly worn down by water and wind over thousands of years. Then, this eroded material is washed into the oceans where it builds into layers of sedimentary rock. Hutton's theories caused much controversy during his time. However, today Hutton's "radical" ideas are so widely accepted that he is known as the "Father of Modern Geology."

On Earth's surface, sedimentary is the most common type of rock.

Fact
or
Fiction
?

Fact

Sedimentary rock is found in every country on Earth!

Name Origin: comes from the Latin sedimentum, which means "act of settling"
Description: When rocks weather, they break down into little bits. After a very long time, these tiny particles can get pressed together to form new rocks.
Significance: These rocks provide the most clues about the history of life on Earth.

Image credits: courtesy of AMNH.