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FOSSILS:
How do we know that there was life millions of
years ago??
Introduction
Fossils are found all around the world.
Scientists that study fossils are called Palentologists
Fossils give us clues to the past
What are fossils?
Fossils
The remains or evidence of living things, traces of past life
What are fossils?
Good Fossil Conditions
1. Objects should be hard: – Bone, teeth, shell, wood (Soft things like flesh, fur and petals don’t make good fossils)
What are fossils?
Good Fossil Conditions
2. Remains need to be there long enough – sometimes the remains get destroyed before a fossil can form
What are fossils?
Good Fossil Conditions
3. Quick burial- air will rot remains– keeps air from rotting remains, and animals from ruining them
What are fossils?
Fossils can be ruined by:
1. Volcanic Activity
What are fossils?
Fossils can be ruined by:
2. Bacterial Rotting
What are fossils?
Fossils can be ruined by:
3. Crushing by other animals
What are fossils?
Fossils can be ruined by:
4. Remains eaten
What are fossils?
Fossils can be ruined by:
5. Weathering & Wave Action (broken down by nature)
Fossil Questions
In what type of rock do fossils typically form?
How do remains become fossilized?
Fossils
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
How do fossils form?
Fossil Formation
A. In sedimentary rock B. Marine animal dies, settles to ocean bottom
C. Remains cover by sediment (body decays)
D. Hard parts protected from air
E. Sediment layers continue to build and compress
F. Erosion uncovers fossil
Types of Fossils
Molds Remains cover with sediment, soft part rots leaving a hollow space
Types of Fossils
Casts Formed when the mold gets filled in with hard sediment
Types of Fossils
Prints Footprints harden in soft mud– Can tell us how it walked, how big, body shape, skin appearance
Types of Fossils
Changed Hard Parts
Actual remains preserved & hardened with minerals
Types of Fossils
Actual Remains
Actual parts of plant or animal is preserved, no rotting– Ex: Freezing, drying, amber, tar
Frozen entire wooly mammoths
Extremely dried out mummies
Insects in hardened tree sap
Hot tar pits that have hardened: La Brea, California
Finding the Age of Fossils
Relative Dating of Fossils
Younger rocks (top layer) are found on top of older rocks (bottom layer)
“LAW OF SUPERPOSITION”
Finding the Age of Fossils
Index Fossils
Fossils that lived during a short period of time
Scientists assume that index fossils of the same type of organism are all nearly the same age.
Can help in aging rock
Finding the Age of Fossils
Absolute Dating of Fossils
Use radioactive elements whose length of break down is known– C-14 and U-238
Finding the Age of Fossils
Fossil Age Rule
A fossil is the same age as the rock that it’s found in
Life on Earth: According to Fossils
What have fossils told us?
Life has existed on Earth for nearly 3 billion years
Life on Earth: According to Fossils
What have fossils told us?
Life forms have changed (evolved)
Life on Earth: According to Fossils
What have fossils told us?
Simple life began in water, evolved, became terrestrial
Life on Earth: According to Fossils
What have fossils told us?
Some organisms have become extinct– Trilobite, Woolly Mammoth, Dinosaurs
Life on Earth: According to Fossils
What have fossils told us?
Some life forms have hardly changed– Ex: Cockroaches, snails, snakes
Assessment
Explain why many animals/plants don’t become fossils?
Many remains are crushed, ruined, eroded, rotted, eaten or burned before they become fossils
Assessment
What types of objects make the best fossils?
Hard parts- teeth, shells, bones, wood
Assessment Describe where most
fossils are formed and how they actually form.
Many fossils form in sedimentary rock that used to be covered by oceans. When organism dies, gets buried by sediment in ocean, soft parts rot, hard parts preserved by sediment
Assessment
Tell about the difference between a mold and a cast
Mold is hollow space left in sediment when animal rots, cast is when mold gets filled back in with other sediment
Assessment
Explain how changed hard parts fossils are formed
When actual body parts fill with minerals changing them to a harder substance
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