8-2 Notes – Early Earth History8-2 Notes – Early Earth History

Chapter 8, Lesson 2Chapter 8, Lesson 2

Life on Earth Changes Paleontologists discovered that the system

used to classify modern organisms could be used to classify fossils.

Life on Earth Changes Fossils from rock layers that are touching

are more similar than fossils from widely separated layers.

Life on Earth Changes The more recent a fossil was formed, the

more it resembles a living organism.

Precambrian Time Precambrian time is 88% of

Earth’s history, and is split into 3 eons: Hadean, Archean, Proterozoic.

88%

Precambrian Time Precambrian rocks are difficult to study

because they are rare, and have undergone metamorphism or been destroyed.

Precambrian Time: Archean Eon Archean Eon sediments contain large

amounts of the minerals pyrite and uraninite.

Precambrian Time: Archean Eon Today’s atmosphere contains oxygen that

quickly destroys these minerals through oxidation.

Precambrian Time: Archean Eon So, we can conclude that Earth’s early

atmosphere had very little oxygen.

Precambrian Time: Archean Eon The absence of oxygen suggests there was

no ozone layer during Precambrian time.

Precambrian Time: Archean Eon Without ozone, ultraviolet rays from the sun

cause death or mutations in cells.

Precambrian Time: Archean Eon Changes in one gene in an organism could

result in new life forms many generations later.

Precambrian Time: Archean Eon Precambrian Time: Archean Eon through Proterozoic Eonthrough Proterozoic Eon

Cyanobacteria are one of the earliest organisms, and they undergo photosynthesis.

Precambrian Time: Archean Eon Precambrian Time: Archean Eon through Proterozoic Eonthrough Proterozoic Eon

Stromatolites are mounds of alternating sediments and cyanobacteria that take in carbon dioxide and release oxygen.

Precambrian Time: Archean Eon Precambrian Time: Archean Eon through Proterozoic Eonthrough Proterozoic Eon

Oxygen levels rose slowly as cyanobacteria and other early-life forms released oxygen.

Natural selection favored organisms that could tolerate or use oxygen.

The amount of ozone in the atmosphere increased.

Precambrian Time: Proterozoic Eon The first invertebrate organisms, animals

without backbones, appeared during the Proterozoic Eon.

These were called Ediacaran fauna, and looked similar to present-day jellies, worms, and corals.

Phanerozoic Eon: Paleozoic Era The first appearance of fossils of organisms

made from hard parts marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon.

Phanerozoic Eon: Paleozoic Era Because hard parts fossilize easier, fossils

are easier to find in Paleozoic rocks than Precambrian rocks.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Cambrian PeriodCambrian Period

The first period in the Paleozoic Era is called the Cambrian Period.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Cambrian PeriodCambrian Period

5 million years into the Cambrian Period, an event called the Cambrian Explosion occurred.

In a short amount of time, the number of animals with shells greatly increased.

Invertebrates such as sponges, jellies, and corals also evolved during the Cambrian explosion.

Changes in trilobite body forms matched changes in the environment.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Cambrian PeriodCambrian Period

A well-preserved 5-inch trilobite specimen from Morocco that swam in the ocean during the Devonian Period roughly 400

million years ago (evolved for over 300 million years)

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Cambrian PeriodCambrian Period

Throughout the Paleozoic era, the oceans contained a wide variety of invertebrate organisms, such as including corals and brachiopods.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian PeriodsOrdovician and Silurian Periods

10-cm. cockroaches, 74-cm. wingspan dragonflies were found on land in the Silurian Period.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian PeriodsOrdovician and Silurian Periods

Vertebrates, animals with backbones, evolved during the early Paleozoic era.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian PeriodsOrdovician and Silurian Periods

The first of these lived in the oceans.– Bony fish with thick fins supported by large

bones and muscles

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian PeriodsOrdovician and Silurian Periods

Plants began spreading onto land as well. Early land plants were small and lived in

moist areas because they could not move water to all their parts.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Ordovician and Silurian PeriodsOrdovician and Silurian Periods

In order to reproduce, amphibians had to return to the water to lay eggs.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Pennsylvanian PeriodPennsylvanian Period

A new organism evolved that could lay its eggs on land.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Pennsylvanian PeriodPennsylvanian Period

Amniotes laid water-tight eggs and could spend all their time on land.– Mammals, dinosaurs, and reptiles evolved from

amniotes.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Pennsylvanian PeriodPennsylvanian Period

Plants with vascular systems that could move nutrients between roots and leaves evolved and spread quickly.

Phanerozoic Eon: Paleozoic Era: Phanerozoic Eon: Paleozoic Era: Pennsylvanian PeriodPennsylvanian Period

Mass Extinctions The Paleozoic Era ended with the late

Permian Period extinction: 90% of marine and 70% of land species.

Mass Extinctions 260 million years ago, the uplifting formation

of Pangaea, or ash and sulfur released from the Siberian Traps may explain the Permian extinction.

Mass Extinctions We don’t know exactly what happened, but

we know global temperatures rose.

GlobalTemperature

Mass Extinctions With most of the larger, predator-type

animals going extinct, other organisms could increase in number, and expand around the world...

Which is not a characteristic of Earth’s early atmosphere during the Precambrian time?

A very little oxygen

B no ozone layer

C iron in minerals quickly oxidized

D organisms were exposed to ultraviolet rays

8.2 Early Earth History

1. A

2. B

3. C

4. D

What were some of the first vertebrates?

A brachiopods

B trilobites

C ediacaran fauna

D bony fish

8.2 Early Earth History

1. A

2. B

3. C

4. D

What ended the Paleozoic era?

A Ordovician extinction

B Devonian extinction

C Permian extinction

D Cambrian extinction

8.2 Early Earth History

1. A

2. B

3. C

4. D

What caused oxygen levels to rise in Earth’s atmosphere?

A the presence of photosynthetic organisms

B the evolution of bacteria-eating organisms

C an increase in the ozone layer

D the evolution of organisms that could tolerate or use oxygen

1. A

2. B

3. C

4. D

The evolution of amniotic eggs allowed ___.

A the spreading of organisms into dry land

B the movement of organisms to shallow-water environments

C the evolution of amphibians

D organisms to live on land and lay eggs in the water

1. A

2. B

3. C

4. D

Which does not characterize the Cambrian explosion?

A an increase in small-shelled organisms

B the evolution of amniotes

C an increase in invertebrates

D an increase in large-shelled organisms

1. A

2. B

3. C

4. D

Events In Earth’s Past (6:11)

Early Earth Organisms Drawings

• For the 2 eons and the 7 periods with a * after their name, draw and color 1 organism that could be found alive during that time.

text p. 326 and 328

Precam

brian

T

ime

Hadeon Eon

Archean Eon *

Proterozoic Eon *

Ph

anero

zoic E

on

Cambrian Period *

Paleo

zoic E

ra

Ordovician Period *

Devonian Period *

Mississipian Period *

Pennsylvanian Period *

Permian Period *

Silurian Period * mass extinction

mass extinction

mass extinction