Q:

Why are fossils only found in sedimentary rocks?

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Quick Answer

Fossils are primarily found in sedimentary rocks because these rocks form at low temperatures and pressures. Igneous rocks form at temperatures and pressures that are high enough to destroy any organic remains. On rare occasions, fossils are found in metamorphic rocks, but they are deformed by the heat and pressure.

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Why are fossils only found in sedimentary rocks?
Credit: Laurence Ireland CC-BY 2.0

Full Answer

The majority of fossils are found in layers of sedimentary rock formed by silt or mud. When an organism dies in an area where its body is protected from scavengers and the elements, its remains are often buried by sediment. Over time, as the sediment is compressed into rock, the remains of the organism decay and dissolve. Minerals seep into the bones and change their chemical makeup. In other cases, the skeleton disintegrates entirely, leaving only a cast that is filled with minerals.

Igneous rocks form from magma at temperatures that are too high for any organic remains to survive. Any organism that is caught in magma is disintegrated and cannot fossilize. Metamorphic rocks are formed from sedimentary or igneous rocks that are heated and subjected to high pressure. If these sedimentary rocks contain fossils, these may survive the metamorphic process. However, the fossils are severely deformed and distorted by the pressure and heat.

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Related Questions

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    Where do sedimentary rocks come from?

    A:

    Sedimentary rocks come from the fragments of pre-existing rocks called sediments. There are three types of sedimentary rocks, each coming from different kinds of sediments. Clastic sedimentary rocks are created from the broken pieces of other rocks, while chemical sedimentary rocks form from mineral crystals like halite and gypsum.

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  • Q:

    What is sedimentary rock?

    A:

    Sedimentary rocks are formed by the deposition of mud, clay, sand and other small particles on the surface of the Earth. Sedimentation can occur in many different environments, including lakes, rivers, deserts and oceans. The sediment is deposited in layers that are compressed over time and turned into solid rock.

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    How long has sedimentary rock been around?

    A:

    As of August 2014, the oldest sedimentary rocks known are banded iron formations from Greenland and Quebec that have been dated to 3.8 or 3.9 billion years old. The material composing these rocks may have been extracted from the Earth's mantle as much as 4.28 billion years ago.

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  • Q:

    What are some resources that can help identify rocks?

    A:

    Identify rocks based on their characteristics or mineral constituents using online tools available at Minerals.net and MinSoCam.org. Confirm findings by matching a rock specimen with photos of known specimens at these websites and at HiddeniteGems.com.

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