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Last Modified: 08/20/09
Lecture Notes

Overheads shown in Lab

Fossils (any evidence of past life) are the key to understanding life of the past. More than that, they provide a wealth of information to the geologist...

Why are fossils important in geology?


Click on the topic below to jump to that section:


Useful Definitions

Paleontology - the study of the geologic history of life on earth
Fossil - any evidence of past life
Body Fossil - the remains of a part of the organism
Trace Fossil - evidence of past life that does not include parts of the organism

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Linnean Classification system

Since (body) fossils are the remains of once-living organisms, fossils are classified in the same manner as living organisms. The classification scheme is hierarchical (p. 240) and is listed below with the broadest (most encompassing) division listed first.

  1. Kingdom
  2. Phylum
  3. Class
  4. Order
  5. Family
  6. Genus
  7. Species

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Body Plans (fossil symmetry, p. 242)

Radial - a radially symmetrical animal can be divided into halves which are mirror images by an infinite number of radially positioned planes.

Bilateral - a bilaterally symmetrical animal can be divided into halves which are mirror images by one plane passing though a certain location. For brachiopods, the plane passes through the center of each valve so that one half of each valve is the mirror image of the other half. In bivalves, the plane passes between the two valves so that the valves are mirror images of each other.

Pentagonal - 5-way symmetry (like a starfish).

Coiled - certain fossils can be identified on the basis of their pattern of coiling.

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Preservation (p. 253)

Best environments for preservation:

  1. Low Energy
  2. Fine-grained sediment
  3. Rapid burial

Why is all that helpful for preservation?

Good question. Well, if it was a high energy enironment (landslide, beach...), the creature would be quickly broken into tiny fragments and scattered--so much for an intact skeleton! Fine-grained sediment acts as nature's "ziploc" bag--it keeps destructive bacteria, acidic waters, etc. from attacking (and destroying) the organic material, bone, etc. of the deceased. Rapid burial places the body far from scavenging creatures (and high energy destructive forces)--giving it the best chance to remain intact and in pristine condition.

Types of fossilization:

1) Fossilization WITHOUT alteration (e.g., frozen Mammoth, insect in Amber)

2) Fossilization of WITH alteration (Body Fossils, p. 253)

3) Trace Fossils - include only signs of the organisms activity; examples include...

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Bias in the Fossil Record (p. 253)

Preservation Bias - hard parts are easier to preserve than soft parts.

Collector's Bias - a paleontologist's objective may be to collect only certain specimens--and therefore what is collected is NOT necessarily representative of the entire, original ecosystem.

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Principles of Stratigraphy (p. 242-3)

  1. Superposition - in undisturbed sedimentary rock layers, younger rocks overlie older rocks.
  2. Original Horizontality - sediments are initially deposited in horizontal layers.
  3. Cross-cutting Relationships - faults and intrusions must be younger than the rocks they cut.
  4. Faunal Succession - assumes that organisms change over time and that a specific body plan is never repeated.

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Index Fossils (p. 257)

How can we age date rocks using fossils?

Through the use of Index Fossils!

Index Fossils are fossils of organisms that were...

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Geologic Time Scale (p. 245 and inside front cover)

Geologic Time Scale

EON

ERA

PERIOD

Phanerozoic

Cenozoic

Quaternary

Tertiary

Mesozoic

Cretaceous

Jurassic

Triassic

Paleozoic

Permian

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

Pre-Cambrian

   
   

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Principle of Uniformitarianism (p. 254)

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