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

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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