Ch. 6.1 Fossils & Geologic Time

Ch. 6.1 – Fossil Evidence of Evolution

Lesson 1-1

• How do scientists know what organisms looked like if they don’t exist anymore?

1. How do fossils form?

• Fossils – remains or traces of prehistoric life

• Fossil record – complete record of all fossils discovered

• Helps us understand how life forms have changed over time.

Carbonization Amber

Petrified wood

Mineralization (petrified):

“turned into stone”

Altered remains: direct evidence

Amber:

hardened resin (sap) of

ancient trees; preserves

delicate insects

Carbonization:

effective in preserving leaves &

delicate animal forms (carbon

film left behind)

Molds:

impression of an organism in a

rock

Cast:

fossil copy of an organism in a

rock

Mold & Cast

Which refers to the impression of an organism

found in a rock?

A. Cast

B. Fossil

C. Mold

D. Trace fossil

Cast

Foss

il

Mold

Trace

foss

il

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Which refers to a fossil that is turned into stone?

A. Carbonization

B. Mineralization

C. Mold

D. Trace fossil

Carboniza

tion

Min

eraliz

ation

Mold

Trace

foss

il

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45

Animal footprints

Copralite (dung &

stomach contents)

Animal burrows (worm

burrow)

Gastrolith (polished

stomach contents)

Altered remains: indirect evidence

Trace fossils:

preserved evidence of the activity of

an organism

Unaltered remains

• Original Materials: original

tissues are preserved– Most common with teeth,

bones, and shells

– Extremely rare to find

remains of an entire animal

– Example: Fully preserved,

frozen mammoth found in

Siberia (Lyuba)

1. How do fossils form? Baby woolly mammoth:4 ft. long

between 10,000 & 40,000 yrs old

Which is the preserved evidence of the activity of

an organism?

A. Cast

B. Fossil

C. Mold

D. Trace fossil

Cast

Foss

il

Mold

Trace

foss

il

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45

Lesson 1-3

• Instead of dating fossils directly, scientists date the rocks the fossils are embedded inside.

• Revisiting the rock cycle:

2. How is geologic evidence used to help determine the age of fossils?

Which kind of rocks are most fossils found in?

A. Igneous rocks

B. Sedimentary rocks

C. Metamorphic rocks

Igneous r

ocks

Sedimenta

ry ro

cks

Meta

morp

hic ro

cks

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Lesson 1-4

• The geologic time scale is a chart that divides Earth’s 4.6 billion year history into different time units.

1. Eons

2. Eras

3. Periods

4. Epochs

2. How is geologic evidence used to help determine the age of fossils?

longest

shortest

Which era and period are we currently in?

A. Mesozoic and Neogene

B. Precambrian and Hadean

C. Cenozoic and Paleogene

D. Cenozoic and Quaternary

Meso

zoic

and Neogene

Preca

mbria

n and H

adean

Cenozoic

and Pale

ogene

Cenozoic

and Quate

rnary

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Lesson 1-5

• Scientists now understand that sudden disappearance in fossils in rock layers are evidence of extinction events.

• Extinction occurs when the last individual organism of a species dies.

• A mass extinction occurs when many species become extinct within a few million years or less.

• Extinctions occur when environments change (either gradually or suddenly).

3. What causes species to change over time?

Evidence of the

meteorite impact

(65 mya)

Lesson 1-5

The fossil record contains evidence that five mass extinction events have occurred during the Phanerozoic eon.

3. What causes species to change over time?

How many major extinction events have occurred in Earth’s history?

A. 2

B. 3

C. 4

D. 5

2 3 4 5

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Lesson 1-5

• As fossils were discovered, patterns emerged that showed many different species with similar body structures.

• Evidence suggests that species change over time.

• Change over time = Evolution (to evolve)

• Biological evolution is the change over time in populations of related organisms.

3. What causes species to change over time?

Lesson 1-5

• The fossil record is evidence that horses descended from organisms for which only fossils exist today.

• There are many other examples of this that we will learn about.