Fossil Types

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Fossil Types

• Chapter 6

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How Do We Know What Happened Millions of Years
Ago?

• Scientists study fossils and look at their
  relationships to rocks they were found in and
  where they were found
• They help to piece together Earths history
• Paleontologists study fossils to put together the
  puzzle of Earths past

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James Huttons Debate

• The Father of Geology
• In 1785 the naturalist James Hutton published his
  theory that the formation of the Earth, its
  mountains and other geological formations must
  have taken millions of years.
• He called his theory uniformitarianism The
  present is the key to the past.

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Huttons Debate Continued

• Huttons theory was not immediately accepted
  because the scientific community had strong
  beliefs in the theory of catastrophism, which
  states that all geologic processes occur suddenly
  and not gradually
• Charles Lyell reintroduced Huttons theory in
  1830, when it was finally accepted

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How Do Fossils Form?

• Fossils are found in sedimentary rocks like
  sandstone, limestone, and shale
• Special conditions need to exist for a fossil to
  form
• Must be protected from scavengers
• Must be protected from bacteria or
  micro-organisms that can speed up the decay
  process
• Must have hard parts like teeth or bones
• Be near water so they can be buried fast

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Petrified Remains

• When minerals replace the original materials of a
  plant or animal
• Essentially, the organism turns to stone
• Sometimes also called permineralization
• Happens to trees and bones/teeth of animals

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Mold and Cast

• Molds form when hard parts of organisms fall into
  soft sediment that eventually turns to rock
• Casts form when a mold gets filled in

Mold
Cast
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Amber

• All leaf-bearing trees release sap (primarily
  conifers or pines).
• When the sap hardens, sometimes insects become
  trapped in this slow-moving, sticky ooze

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Coprolites and Gastroliths

• Gastroliths are stomach stonesanimals swallow
  stones to help digest their food
• Coprolites are formed from feces of animals
• Both of these, along with animal tracks and
  burrows, are considered trace fossils, which
  indicate the activity of the animal

Gastroliths are all very well polished
Doesnt that really look like poop?!
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Mummified

• Fossils that form this way are usually found in
  hot or cold deserts
• Organisms dont go through a decay processthey
  just dry out
• The lack of moisture in the air in combination
  with both heat and wind dry out the flesh and
  create a leather texture preserving the organism.

Mummified dinosaur remains
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Ice and Tar

• Always find well preserved remains
• Both are considered to be original remains
• Find the original organism parts intact
• The wooly mammoth and saber-toothed tiger are the
  best remains that have been found

Saber-toothed Cat skull from the La Brea Tar Pits
in CA
Actual wooly mammoth hairs found preserved in
Siberian ice
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Carbonaceous Fossil

• A carbonaceous fossil is made when pressure and
  heat force out gases and liquids, leaving a thin
  residue of the organism.
• Very often happens to plants

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Index Fossils

• Index fossils are fossils of organisms that lived
  for a short period of time, but could be found
  all over the world.
• The best index fossils are of trilobites.
• Trilobites look like a cross between a horseshoe
  crab and a pill bug.
• They were only around for about 20 million years,
  and geologically speaking, that isnt that long!

Trilobite
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Can You Name That Fossil?
1 2 3
4 5 6
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Answers to Can You Name That Fossil?

• 1. Petrified remains
• 2. Carbonaceous film
• 3. Amber
• 4. Cast
• 5. Mold
• 6. Trace/Animal Track