Focus On Life Science

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Chapter Menu
Lesson 1 Geologic Time and Mass
Extinction Lesson 2 Early Earth History Lesson
3 Middle and Recent Earth History
Click on a hyperlink to view the corresponding
lesson.
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8.1 Geologic Time and Mass Extinction

• index fossil
• mass extinction
• catastrophic event

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Development of the Geologic Time Scale
8.1 Geologic Time and Mass Extinctions

• The changes that have occurred in Earths history
  are recorded on a time line called the geologic
  time scale.

• The time scales units are uneven because
  extinctions, growth rates, and environmental
  changes happen at different rates.

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Index Fossils
8.1 Geologic Time and Mass Extinctions

• An index fossil is the remains of a species that
  existed over vast regions of Earth for a short
  period of time.

• Special criteria are used to identify index
  fossils.

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Index Fossils (cont.)
8.1 Geologic Time and Mass Extinctions
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Divisions of the Geologic Time Scale
8.1 Geologic Time and Mass Extinctions

• No two divisions of time have the same number of
  years.

• The largest divisions are eons, then eras,
  periods, and epochs.

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Eras
8.1 Geologic Time and Mass Extinctions

• The Phanerozoic eon is divided into three eras.

• Paleozoic era dominated by invertebrate marine
  organisms
• Mesozoic era dinosaurs and mammals lived on
  land
• Cenozoic era humans evolved, continues today

Phanerozoic Eon Part A Part BPart C Part D
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Periods and Epochs
8.1 Geologic Time and Mass Extinctions

• The Cenozoic era is divided into the Paleogene,
  Neogene, and Quaternary periods.

• The Quaternary period began 1.8 million years ago
  and is divided into epochs.
• The Pleistocene epoch ended about 8,000 years
  ago, and we now live in the Holocene epoch.

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What are mass extinctions?
8.1 Geologic Time and Mass Extinctions

• Mass extinction is the dying off of many species
  at one time.

• A greater abundance of fossils in one rock layer
  compared to other layers indicates a mass
  extinction.
• Mass extinctions happen over a great span of time.

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Possible Causes of Mass Extinctions
8.1 Geologic Time and Mass Extinctions

• A catastrophic event causes drastic change in the
  numbers of organisms of species over a short
  period in geologic time.

• Not all catastrophic events cause mass
  extinction.
• Types of events that can cause mass extinction
  include changes in climate, volcanic eruptions,
  and asteroid impacts.

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Climate Change
8.1 Geologic Time and Mass Extinctions

• There is evidence that some mass extinctions were
  caused by sudden climate change.

• Species that cannot survive a change in climate
  become extinct.
• Climate change can be caused by volcanic
  eruptions or asteroid impacts, and can result in
  global warming or cooling.

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Global Warming
8.1 Geologic Time and Mass Extinctions

• Greenhouse gases in the atmosphere may contribute
  to global warminga global increase in
  atmospheric temperature.

• Global warming causes a decrease in oxygen levels
  in water, and an increase in sea levels.

• May have been the cause for the Devonian mass
  extinction

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Global Cooling
8.1 Geologic Time and Mass Extinctions

• Global cooling could lower sea levels as more
  water is frozen in glacial ice.

• Less water means fewer warm, shallow-water
  environments.

• May have initiated the Ordovician mass extinction

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Volcanoes
8.1 Geologic Time and Mass Extinctions

• Eruptions can be explosive or non-explosive.

• The dust, ash, lava, and gas emitted from
  volcanic eruptions can affect climate and
  organisms.
• A volcanic eruption is one hypothesis proposed to
  explain the mass extinction at the end of the
  Cretaceous period.

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Basalt Flows
8.1 Geologic Time and Mass Extinctions

• Non-explosive floods of molten basalt emit the
  largest volume of matter of any eruptions.

• Geologic evidence shows that large basalt flows
  occurred during the Permian and Cretaceous mass
  extinctions.

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Volcanic Haze
8.1 Geologic Time and Mass Extinctions

• The gases produced by basalt flows cause a
  volcanic haze effect.

• Sulfur dioxide gas is released and acid clouds
  form, preventing the Suns ultraviolet rays from
  reaching Earth.
• Global cooling occurs over months and years.
• Heat becomes trapped in the atmosphere and global
  temperatures increase.

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Asteroid Impacts
8.1 Geologic Time and Mass Extinctions

• Scientists believe an asteroid impact in Mexico
  may have contributed to the Cretaceous mass
  extinction.

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Asteroid Impacts (cont.)
8.1 Geologic Time and Mass Extinctions

• Scientists propose that this impact sent enough
  dust and materials into the atmosphere to block
  sunlight.

• Global cooling after the impact turned to global
  warming as carbon dioxide was released from
  burning plants.

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The Debate
8.1 Geologic Time and Mass Extinctions

• Evidence supports the idea that many species
  became extinct at the end of the Cretaceous
  period because of asteroids.

• But the impact did not cause all the extinctions.
• Many species became extinct before the impact,
  and the rate of extinction was increasing before
  the impact.

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Lesson 1 Review
8.1 Geologic Time and Mass Extinctions

1. A
2. B
3. C
4. D

Which describes the divisions of the geologic
time scale in order of longest to shortest units
of time? A eons, eras, periods, epochs B eons,
epochs, eras, periods C epochs, eons,
periods, eras D epochs, eons, eras, periods
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Lesson 1 Review
8.1 Geologic Time and Mass Extinctions

1. A
2. B
3. C
4. D

What is the likely immediate outcome of an
explosive volcanic eruption that sends dust into
the atmosphere? A global warming B global
cooling C basalt flows D volcanic haze
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Lesson 1 Review
8.1 Geologic Time and Mass Extinctions

1. A
2. B
3. C
4. D

What type of eruption emits the largest volume of
matter? A basalt flows B explosive eruptions
C non-explosive eruptions D volcanic haze
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End of Lesson 1
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8.2 Early Earth History

• cyanobacteria
• vertebrate
• amniote

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Life on Earth Changes
8.2 Early Earth History

• Paleontologists discovered that the system used
  to classify modern organisms could be used to
  classify fossils.

• Fossils from rock layers that are touching are
  more similar than fossils from widely separated
  layers.
• The more recent a fossil was formed, the more it
  resembles a living organism.

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Life on Earth Changes (cont.)
8.2 Early Earth History
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Precambrian Time
8.2 Early Earth History

• Precambrian rocks are difficult to study because
  they have undergone metamorphism or been
  destroyed.

• Precambrian fossils are not abundant but provide
  a lot of information about Earths early
  atmosphere and environment.

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The Precambrian Atmosphere
8.2 Early Earth History

• Archean sediments contain large amounts of pyrite
  and uraninite.

• Todays atmosphere contains oxygen that quickly
  destroys these minerals through oxidation.
• Earths early atmosphere had very little oxygen.

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Ozone
8.2 Early Earth History

• The absence of oxygen suggests there was no ozone
  layer during Precambrian time.

• Without ozone, ultraviolet rays cause death or
  mutations in cells.
• Changes in one gene in an organism could result
  in new life forms many generations later.

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The First Organisms
8.2 Early Earth History

• Cyanobacteriaone of the earliest organisms.

• Stromatolites are mounds of alternating
  thin-layered sediments and photosynthetic
  cyanobacteria that take in carbon dioxide and
  release oxygen.

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A Changing Environment
8.2 Early Earth History

• 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.

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Soft-Bodied Organisms
8.2 Early Earth History

• The first invertebrate organismsanimals without
  backbonesappeared during the Proterozoic eon.

• Ediacaran fauna

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The Paleozoic Era
8.2 Early Earth History

• The first appearance of fossils of organisms made
  from hard parts marks the end of the Proterozoic
  eon.

• Because hard parts fossilize easier, fossils are
  easier to find in Paleozoic rocks than
  Precambrian rocks.

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The Cambrian Explosion
8.2 Early Earth History

• During a relatively short period of time, the
  number of animals with shells greatly increased.

• Invertebratessponges, jellies, coralsalso
  evolved during the Cambrian explosion.

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Invertebrates of the Paleozoic Era
8.2 Early Earth History

• Throughout the Paleozoic era, the oceans
  contained a wide variety of invertebrate
  organisms.

• Corals, brachiopods, crinoids, bryozoans
• Ordovician period, Silurian period

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Vertebrates of the Paleozoic Era
8.2 Early Earth History

• Vertebratesanimals with backbones evolved
  during the early Paleozoic era.

• The first of these lived in the oceans.

• Bony fish with bony rays that supported their
  fins
• Bony fish with thick fins supported by large
  bones and muscles

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A New Egg
8.2 Early Earth History

• A new organism that could lay its eggs on land
  evolved during the early Pennsylvanian period.

• Amniotes laid water-tight, amniotic eggs and
  could spend all their time on land.

• Mammals, dinosaurs, and reptiles evolved from
  amniotes.

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Plants of the Paleozoic Era
8.2 Early Earth History

• During the Ordovician period, plants began
  spreading onto land.

• Early land plants were small and lived in moist
  areas because they could not move water to all
  their parts.

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Plants of the Paleozoic Era (cont.)
8.2 Early Earth History

• Plants with vascular systems that could move
  nutrients between roots and leaves then evolved.

• New plants developed quickly.

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Paleozoic Extinctions
8.2 Early Earth History

• The Paleozoic era ended with the late Permian
  extinction90 of marine and 70 of land species.

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Paleozoic Extinctions (cont.)
8.2 Early Earth History

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

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Lesson 2 Review
8.2 Early Earth History

1. A
2. B
3. C
4. D

Which is not a characteristic of Earths 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
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Lesson 2 Review
8.2 Early Earth History

1. A
2. B
3. C
4. D

What were some of the first vertebrates? A brachio
pods B trilobites C edicacaran fauna D bony fish
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Lesson 2 Review
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
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End of Lesson 2
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8.3 Middle and Recent History

• pterosaur
• ectotherm
• endotherm
• gymnosperm
• primate

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A Changing Landscape
8.3 Middle and Recent Earth History

• 180 million years ago, Pangaea began to split
  into Laurasia and Gondwanaland.

• This created a warm, wet climate.

What geologic evidence supports the existence of
Pangaea?
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A Changing Landscape (cont.)
8.3 Middle and Recent Earth History
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A Changing Landscape (cont.)
8.3 Middle and Recent Earth History

• The Mesozoic era is known as the Age of Reptiles.

• Dinosaurs dominated midway through the era.
• Toward the eras end, land began to dry out and
  the largest dinosaurs became extinct.
• Mammals that had never been larger than a possum,
  took over as the dinosaurs went extinct.

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Invertebrates of the Mesozoic Era
8.3 Middle and Recent Earth History

• Stromatolites increased in number after their
  predators became extinct at the end of the
  Paleozoic era.

• Algae and rudistids evolved in the Cretaceous
  period.
• Reef-building corals replaced rudistids in the
  Triassic period.
• Insects declined in number and diversity during
  the Mesozoic era.

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Vertebrates of the Mesozoic Era
8.3 Middle and Recent Earth History

• The oceans contained predatory reptiles, and
  amphibians, reptiles, and mammals that lived on
  land continued to evolve.

• Frog, turtles, crocodiles, dinosaurs
• Pterosaursflying reptileswere different from
  dinosaurs, not related to birdsor bats

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Dinosaurs
8.3 Middle and Recent Earth History

• The first dinosaurs were small, but new species
  evolved into some of the largest animals to walk
  the Earth.

• Ectothermsanimals that rely on their
  surroundings and behavior to help them regulate
  their body temperature

• Endothermsanimals that generate internal body
  heat to maintain a constant body temperature

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Dinosaurs (cont.)
8.3 Middle and Recent Earth History

• Scientists think dinosaurs lived more like
  todays mammals and birds than like reptiles.

• A dinosaurlike skeleton with fossilized feathers
  found in Jurassic-aged rocks supports the idea
  that birds evolved from dinosaurs.

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Mammals
8.3 Middle and Recent Earth History

• Early mammals were small and not numerous for
  most of the Mesozoic era.

• In the Cretaceous period, they began to increase
  in number and diversity.

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Plants of the Mesozoic Era
8.3 Middle and Recent Earth History

• Gymnospermsplants that produce seeds but no
  flowerswere the dominant plants of the Mesozoic
  era.

• Angiospermsflowering plants that bear seeds with
  hard coveringsevolved near the end of the
  Mesozoic era.

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Mesozoic Era Extinction Events
8.3 Middle and Recent Earth History

• Mass extinctions occurred at the end of the
  Triassic and Jurassic periods.

• At the end of the Cretaceous period, an
  extinction event caused 85 of all ocean species
  and the remaining dinosaurs to become extinct.
• Many mammal species survived.

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The Cenozoic Era
8.3 Middle and Recent Earth History

• The Cenozoic era is divided into seven epochs.

• During the Cenozoic era, marine life began to
  recover from the Cretaceous mass extinction.
• The offspring of organisms that survived the
  Cretaceous extinction make up todays marine
  ecosystems.

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Animals on Land
8.3 Middle and Recent Earth History

• Some mammals returned to the ocean during the
  Eocene epoch, giving rise to marine mammals such
  as whales.

• Primatesanimals with opposable thumbs and eyes
  that look forwardevolved during the Eocene epoch
  and rapidly diversified.

• Hominidsanimals which walk upright on two
  legsevolved from the early primates during the
  Pliocene epoch.

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Plants of the Cenozoic Era
8.3 Middle and Recent Earth History

• Flowering plants have continued to evolve since
  the Mesozoic era.

• Grasses supported a large diversity of mammals,
  allowing mammals to multiply and diversify.

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Lesson 3 Review
8.3 Middle and Recent Earth History

1. A
2. B
3. C
4. D

Which era is known as the Age of
Reptiles? A Cretaceous B Mesozoic C Cenozoic
D Jurassic
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Lesson 3 Review
8.3 Middle and Recent Earth History

1. A
2. B
3. C
4. D

What best describes how dinosaurs are viewed
today? A ectotherms B endotherms C reptiles D bird
s
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Lesson 3 Review
8.3 Middle and Recent Earth History

1. A
2. B
3. C
4. D

During which epoch did hominids
evolve? A Pliocene B Eocene C Cenozoic
D Cretaceous
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End of Lesson 3
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Chapter Resources Menu
Chapter Assessment California Standards
Practice Concepts in Motion Image Bank Science
Online Interactive Table Virtual Lab
Click on a hyperlink to view the corresponding
feature.
66
Chapter Assessment 1

1. A
2. B
3. C
4. D

Which is not an effect of an asteroid
impact? A sunlight blocked by dust B basalt flows
causing a complex sequence of events C carbon
dioxide causing global warming D the death of
primary producers causing mass extinctions
67
Chapter Assessment 2

1. A
2. B
3. C
4. D

Why have some paleontologists proposed that
asteroid impacts did not cause all the mass
extinctions at the end of the Cretaceous
period? A There is no evidence of an asteroid
impact at the end of the Cretaceous
period. B Volcanic haze is a more likely
cause. C Many species were already extinct by
the time of the impact. D The fossil record does
not support a mass extinction at the end of
the Cretaceous period.
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Chapter Assessment 3

1. A
2. B
3. C
4. D

What caused oxygen levels to rise in Earths
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
69
Chapter Assessment 4

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
70
Chapter Assessment 5

1. A
2. B
3. C
4. D

Which group declined in number and diversity
during the Mesozoic era? A stromatolites B reef-bu
ilding corals C insects D mammals
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CA Standards Practice 1

1. A
2. B
3. C
4. D

Which is not one of the methods scientists use to
divide the geologic time scale into units of
time? A mass extinctions B major changes in
life-forms C index fossils D major changes in
climate
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CA Standards Practice 2
SCI 4.g

1. A
2. B
3. C
4. D

What is not a possible effect of global
warming? A increase in sea levels B decrease in
oxygen levels C decrease in shallow-water
environments D rising atmospheric
temperatures
73
CA Standards Practice 3
SCI 4.d

1. A
2. B
3. C
4. D

Which is not a reason Precambrian rocks are
difficult to study? A many have been
destroyed B many have undergone
metamorphosis C they are difficult to date
with radiometric dating D they do not provide
much information
74
CA Standards Practice 4
SCI 4.g

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
75
CA Standards Practice 5
SCI 4.b

1. A
2. B
3. C
4. D

All remaining dinosaurs became extinct at the end
of which period? A Triassic B Jurassic
C Cretaceous D Mesozoic
76
Concepts in Motion 1
77
Image Bank
78
Interactive Table
Phanerozoic Eon Part A Part BPart C Part D
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End of Resources