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Notes SPI 0807.5.5 Fossils

DEC 2012

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

PRESS THE RIGHT-ARROW BUTTON ON YOUR KEYBOARD

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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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Notes SPI 0807.5.5 Fossils

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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Notes SPI 0807.5.5 Fossils

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

Notes SPI 0807.5.5 Fossils

Science

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

(Also known as petrifaction)

Example:Petrified Wood 1

Example:Petrified Wood

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.

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Notes SPI 0807.5.5 Fossils

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)

Notes SPI 0807.5.5 Fossils

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: 40, 000 yrs old

Frozen Baby Mammoth(From Siberia, Russia)Approx. 42,000 yrs old 1

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Notes SPI 0807.5.5 Fossils

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.

Trace FossilImprint Of A Fish

(Also called ichnofossils)

Trace Fossil Dinosaur footprints

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Notes SPI 0807.5.5 Fossils

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

Mold Fossil Cast Fossil

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Notes SPI 0807.5.5 Fossils

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: Ammonite fossils

Example: Trilobite fossils

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Notes SPI 0807.5.5 Fossils

Science

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

Layer A

Layer B

Layer C

B is older than A

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…called the law of superposition

So fossil one is older than fossil two