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SPI 0807.5.5 Fossils
Notes
Science

• What Are Fossils?
• The preserved physical remains of deceased
  organisms that are at least 10,000 years old
• NOTE Most organisms do not become fossils when
  they die
• NOTE The formation of fossils is a rare event
• How Are Fossils Formed?
• Watch this amusing video Link Video How
  Fossils Are Made

8 Types of Fossils
A) Fossils In Rocks
E) Frozen Fossils
B) Fossils In Amber
F) Trace Fossils
C) Petrified Fossils
G) Mold/Cast Fossils
D) Fossils In Asphalt
H) Index Fossils
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SPI 0807.5.5 Fossils
Images
Science
(See p141 Fig 2)
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SPI 0807.5.5 Fossils
Notes
Science

• A) Fossils In Rocks
• Found in sedimentary rock
• An organism died was covered with mud, dirt,
  sand, ash, etc.
• Later the mud, dirt, sand, or ash became
  sedimentary rock

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SPI 0807.5.5 Fossils
Notes
Science

• B) Fossils In Amber
• Tree sap fell on a small organism, enclosed it,
  killed it
• Over time the sap hardened into amber
• The amber became covered with mud, dirt, sand,
  ash, etc.

Example Insects In Amber
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SPI 0807.5.5 Fossils
Notes
Science
(Also known as petrifaction)

• C) Petrified Fossils
• Organism died- then was covered with mud, dirt,
  sand, ash, etc.
• The structure of the organism was replaced with
  minerals

Sometimes when wood is buried, groundwater will
flow through the sediment and deposit minerals in
the cells of the wood.
The wood rots away the minerals remain in the
shape of the tree.
Example Petrified Wood
Example Petrified Wood
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SPI 0807.5.5 Fossils
Notes
Science

• D) Fossils In Asphalt
• Animals fell into tar pits, were trapped, and
  died
• The asphalt hardened preserving skeletons,
  shells, teeth, etc.

Saber Tooth Tiger Fossil (From La Brea Tar
Pits, California)
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SPI 0807.5.5 Fossils
Notes
Science

• E) Frozen Fossils
• Animals died in a cold climate region and were
  frozen
• The cold temperatures preserved both soft and
  hard parts
• Many mammoths became frozen during the last ice
  age

Frozen Baby Mammoth (From Siberia,
Russia) Approx. 42,000 yrs old
Frozen Baby Mammoth (From Siberia,
Russia) Approx 40, 000 yrs old
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SPI 0807.5.5 Fossils
Notes
Science

• F) Trace Fossils
• Are impressions or traces left by plants and
  animals
• Can be simple tunnels or burrows in the mud
• Can be footprints or imprints in the mud etc.

(Also called ichnofossils)
Trace Fossil Imprint Of A Fish
Trace Fossil Dinosaur footprints
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SPI 0807.5.5 Fossils
Notes
Science

• G) Mold/Cast Fossils
• In sediment, ground water may dissolve shells,
  leaving a shape called a mold
• Sometimes the shell dissolves and is replaced by
  minerals, leaving behind a mineral cast of the
  fossil

Cast Fossil
Mold Fossil
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SPI 0807.5.5 Fossils
Notes
Science

• H) Index Fossils
• A way to relatively date rocks
• Some fossils are commonly found at certain strata
  levels across large geographic areas

(A.K.A. relative dating)
we call these index fossils

Example Trilobite fossils
Example Ammonite fossils
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SPI 0807.5.5 Fossils
Notes
Science

• Sedimentary rock and fossils
• deeper layers are older than layers above it.
• Example See three layers belowLayer A, Layer B,
  and Layer C
• Layer C is older than layer B.
• So fossils in deeper layers are older than
  fossils above it.

called the law of superposition
B is older than A
So fossil one is older than fossil two
Layer A
3
Layer B
2
Layer C
1