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Fossils - Chapter 3, Section 4 Notes

April 22, 2015

Chapter 3, Section 1 Notes

A. Paleontology – The Study of Past Life

1. The science involved with the study of past life is called paleontology.

2. Scientists who study this past life are called paleontologists.

3. Fossils are the data that scientists use to study the past life.

4. Fossils are the remains of organisms preserved by geological processes.

5. Paleontologists can study particular organisms, plants, or animals.

Chapter 3, Section 4 Notes: Looking at Fossils

A. Fossilized Organisms

1. The remains or physical evidence of an organism preserved by geological processes is called a fossil.

2. Fossils are most often preserved in sedimentary rocks but other materials also preserve evidence of past life.

          a. Fossils in Rocks

  • Dead organisms are eaten by other organisms or decay.
  • Organisms can be buried in sediment to slow down decay.
  • Harder parts are slow to decay so soft tissues are quickly decaying.

b. Fossils in Asphalt

  • Asphalt will well up at the Earth’s surface leaving thick, rocky ponds.
  • Asphalt will trap and preserve many kinds of organisms over a long period of time.
  • Organisms trapped in asphalt help scientists study about past environments.

c. Fossils in Ambers

  • Organisms can be caught in soft, sticky tree sap that hardens.
  • Hardened tree sap is called amber.
  • Hardened tree sap will preserve organisms.

d. Frozen Fossils

  • Cold temperatures preserve many types of frozen fossils from the last ice age.
  • Frozen fossils tell about the animal and the environment in which the anima lived.
  • Cold temperatures slow down decay.

e. Petrification

  • Petrification is the process in which the mineral replaces an organism’s tissue.
  • Permineralization is the process in which the pore space in an organism’s hard tissues (like bone or wood) is completely replaced by minerals.
  • Replacement is a process in which the organism’s tissues are completely replaced by minerals.

Some fossils aren’t part of an organism like trace fossils, molds, or casts.

a. Trace Fossils

  • Any naturally preserved evidence of animal activity is called a trace fossil.
  • Trace fossils form when animal footprints fill with sediment and become preserved in rock. These types of fossils tell about the animals that made them.
  • Another type of trace fossil are burrows or the shelters made by animals that are buried in sediment.

b. Molds and Casts

  • Molds are cavities in rocks where a plant or animal is buried; cavity in rock made by a shell or other body.
  • Cast is an object created when sediments fill with mold and becomes rock.

C. Using Fossils to Interpret the Past

1. The Information in the Fossil Record

a. fossil record offers a sketch of Earth’s history with some parts being more complete than others.

b. The fossil record is incomplete since some organism still need to be fossilized or discovered.

2. History of Environmental Changes

a. fossil record reveals a history of environment change or describe past climates

3. History of Changing Organisms

a. Scientists can study how life has changed over time by studying the organisms between layers.

b. Paleontologists fill in missing information about changes in organisms in the fossil record by looking for _similarities between fossilized organisms  and their closest living relatives.

D. Using Fossils to Date Rocks

1. Specific fossils are found only in certain layers_ of rocks that are dated to determine the time span in which the organisms that formed the fossils lived.

2. Index fossils are fossils of organisms that lived during a relatively short, well-defined geologic time span.

  • This type of fossil appears in a limited range of rock layers.
  •  Fossil must be found in several layers throughout the world to be considered an index fossil.
  • Examples are ammonites or tribolites.

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