Ch. 23 Sec. 2

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Ch. 23 Sec. 2

• The Mesozoic Era

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• Reptiles became the dominant terrestrial animals
  during the Mesozoic while Pangaea broke apart.

Review Vocabulary
subduction the process by which one tectonic
plate descends beneath another
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• The mass extinction event that ended the
  Paleozoic Era ushered in new opportunities for
  animals and plants of the Mesozoic Era. While
  some groups of these organisms that lived during
  the Mesozoic Era remain on Earth today, none of
  the giant reptiles that dominated the land, sea,
  and air and typified the period survived.

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Section 23.2
Although dinosaurs are the most famous of the
Mesozoic life-forms, other organisms also
appeared during this era.
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I. Mesozoic Paleogeography
A. Breakup of Pangaea
When the Mesozoic Era began, a single global
ocean and a single continentPangaea defined
Earths paleogeography. During the middle
Triassic Period, Pangaea began to break apart.
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• Heat beneath Pangaea
• a. Tropical climate
• Continent expands
• Lithosphere began to crack
• a. Rifts widened
• b. Landmass began spreading apart

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B. Seaways

• Atlantic Ocean
• a. Early Triassic
• b. Mid-Atlantic Ridge
• 2. Red Sea Gulf of Aden

Fig. 23.9 page 656
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C. Changing sea level

• Rift systems were partly responsible for a rise
  in sea level during the Mesozoic
• a. Magma displaced seawater
• Sea level dropped at the end of the Triassic
• a. Desertlike conditions in western North
  America

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3. Sea level rose again during the
Jurassic a. Shallow sea formed in North
Americas center 4. The ocean continued to rise
during the Cretaceous a. Covered much of
North Americas interior
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Nearly one-third of Earths land surface was
covered with water during the late Cretaceous.
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II. Mountain Building Western Laurentia

• Cordillera Orogeny three phases
• Caused by the subduction of the oceanic Farallon
  Plate beneath Laurentias western margin

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1. Sierra Nevadas

1. Late Jurassic and early Cretaceous
2. Subduction proceeded slowly
3. Oceanic plate descended at a steep angle
   producing magma

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2. Rocky Mountains

• a. Subduction increased in speed
• Plate descended at a shallow angle
• Less volcanism/more thrust faulting

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3. Rocky Mountain Extension

1. Late Cretaceous into the Cenozoic
2. The angle of subduction was even more shallow
3. The shallow angle was caused by rapid subduction
4. Lack of volcanism/vertical uplift

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During the three phases of the Cordilleran
Orogeny, mountains formed farther inland as the
angle of subduction became more shallow and the
speed increased, causing massive
faulting and uplift.
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III. Mesozoic Life
As Pangaea broke apart during the early Mesozoic,
much of the habitat on the continental shelves
that was lost during Pangaea's formation once
again became available. New marine organisms,
ranging from large predatory reptiles to tiny
photosynthetic phytoplankton, evolved to fill
these niches.
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Phytoplankton were, and are today, microscopic
organisms at the base of the marine food chain.
These organisms were abundant during the
Cretaceous. The remains of their shell-like hard
parts are found in chalk deposits worldwide.
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A. Plant life

• Jurassic - plant life changed sharply
• Temperate swamps dried as the climate warmed
• a. Tall cycad trees
• b. ginkgos
• c. pine trees and other conifers

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3. Cretaceous

• a. Flowering plants appear

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B. Terrestrial animals

• Reptiles
• Amniotic eggs
• a. Shell
• b. Contain food water for embryo
• c. Allows for colonization of land

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3. Dinosaurs Archosaurs are a group of reptiles
which includes dinosaurs and crocodilians.
Archosaurs have a hip structure that allows the
legs to be held underneath the body. This enabled
some archosaurs to run with an upright posture.
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C. Mass extinction
Evidence of a large meteorite impact exists in a
clay layer that separates Cretaceous rocks from
rocks of the first period of the Cenozoic. Found
worldwide, this layer contains an unusually high
amount of iridium, a rare metal in Earths rocks
but a relatively common metal in asteroids.
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Section 23.2
The Mesozoic Era
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Reptiles became the dominant terrestrial
animals during the Mesozoic while Pangaea broke
apart.

• The breakup of Pangaea triggered a series of
  tectonic events that transformed western
  Laurentia.
• The Atlantic Ocean began to form during the
  Mesozoic as North America broke away from Europe.

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• Dinosaurs and other new organisms evolved to fill
  niches left empty by the Permo-Triassic
  Extinction Event.
• All dinosaurs, except birds, along with many
  other organisms became extinct during a mass
  extinction event at the end of the Mesozoic.