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Where do fossils form?

Dinosaur fossils are found in rocks, but not all rocks. All rocks fall into one of three groups: sedimentary, igneous, or metamorphic.

Finding dinosaurs requires a lot of patience and good luck. Dinosaurs are not where the paleontologists want them to be, but where the dinosaur died many millions of years ago. They are usually found in sedimentary rock, but not in every sedimentary rock.
Sedimentary rocks are formed from particles of other rocks such as sand, limestone, and mud. The sedimentary rocks in which fossils are found were deposited in environments such as ancient rivers, swamps, lakes, and ocean bottoms. These particles pile up and form layers. The layers eventually harden into rock due to the weight of particles on top of them, water dissolving, and minerals from the dissolved water being left behind which become a part of the rock.

Igneous rocks were once melted material called magma, which forms deep underneath the surface of the earth. The temperature is very high where magma forms, which is why it is melted. When the magma cools underneath the surface of the earth it is called plutonic rock. Magma can also cool at the surface of the earth when pressure builds up inside the earth and it is forced through a volcano. This is called lava.

Metamorphic rocks are changed rocks. Any rock can become a metamorphic rock if a lot of heat and pressure is applied to it. This change occurs because minerals in the rock react with each other as a result of the added heat and pressure. This metamorphosis always takes place deep below the surface of the earth. Sometimes metamorphic rocks are exposed due to the erosion of the rock lying on top of them.

Go on a virtual dinosaur dig!

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