The Fossil Record Smart.notebook April 11, 2018

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Fossils: The remains of animals or plants that lived in a previous geologic time.

Important for determining relative and absolute ages of rocks.

The study of fossils is called paleontology.

Almost all fossils are found in sedimentary rock. Sediments that cover the fossils slow or stop the process of decay.

In general, only the hard parts of organisms (wood, bones, shells and teeth), become fossils.

The Fossil Record Smart.notebook April 11, 2018

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Interpreting the Fossil Record

The fossil record can provide information about Earth’s geologic history.

Fossils show how organisms have changed over thousands of years; this can indicate environmental changes of the Earth’s past.

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How Fossils Form

Mummification: Found in dry places, because decomposing bacteria cannot survive there.

Amber: Insects sometimes become trapped in tree sap. When the tree sap hardens, the amber can protect the insect. DNA has been recovered from some amber specimens.

Tar Seeps: Tar seeps form when thick petroleum oozes to the surface. Often they are covered by water. Animals coming to drink the water sometimes become trapped and die. The petroleum covers the animals and preserves them.

The Fossil Record Smart.notebook April 11, 2018

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How Fossils Form continued

Freezing: Most bacteria cannot survive freezing temperatures.

Organisms that are buried in frozen soil or ice do not decay.

Petrification: Mineral solutions like groundwater replace the organic material that were covered in sediment.

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Types of Fossils

Imprints ­­ Original organic material like a leaf or fish can leave a carbonized imprint in soft sand or mud. An imprint displays the surface features of the organism.

Molds and Casts ­­ A cast is a replica of the original organism.

When a shell is buried, its remains eventually decay and leave an empty space. When sand or mud fills a mold and hardens, a natural cast forms.

The Fossil Record Smart.notebook April 11, 2018

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Types of Fossils Continued

Coprolites ­­ Fossilized dino dung. Scientists study coprolites to determine the feeding habits of dinosaurs and other ancient animals.

Gastroliths ­­ Some dinosaurs had stones in their digestive systems to help grind their food. Gastroliths are identified by their smooth, polished surfaces and their proximity to dinosaur remains.

Trace Fossil ­­ A fossilized footprint, track, or burrow in sedimentary rock.

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Index Fossils

Index Fossils ­­ Fossils that occur only in rock layers in a particular geologic age.

Must be present over a large region

Easily identifiable.

Lived during a short geologic time.

Must be common in the rock layers.

Index fossils can be used estimate absolute ages of specific rock layers.

Geologists also use index fossils to locate rock layers that are likely to contain oil and natural gas deposits.