Geology 105: Earthquake and Continental Drift
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Questions and Answers

What was Wegener's main conclusion about the continents?

  • Continents originate from underwater volcanic activity.
  • Continents drifted only in the last 100 million years.
  • The continents were once part of a single larger continent. (correct)
  • The continents are fixed and do not move.

Which evidence did Wegener use to support his theory of continental drift?

  • The different climate zones on each continent.
  • Mountains that are the same age present on all continents.
  • Fossils of the same species found on different continents. (correct)
  • The similarity of languages spoken in different continents.

What was the name of the super-continent that Wegener theorized existed around 300 million years ago?

  • Pangea (correct)
  • Lemuria
  • Atlantis
  • Gondwanaland

How did Wegener explain the distribution of ancient corals and coal?

<p>They existed in a warm tropical climate that once covered those areas. (A)</p> Signup and view all the answers

What is the primary mechanism thought to drive continental drift?

<p>Heat from the Earth's core causing mantle convection. (C)</p> Signup and view all the answers

Which of the following observations would NOT support Wegener's theory of continental drift?

<p>Mountain ranges that do not match in geological age across continents. (A)</p> Signup and view all the answers

According to Wegener's hypothesis, how did the continents appear to move since their initial formation?

<p>They were pushed by tectonic forces. (D)</p> Signup and view all the answers

What is one method in the scientific process that Wegener likely used when developing his theory?

<p>Gathering further data to test existing hypotheses. (D)</p> Signup and view all the answers

What does the inclination of magnetic minerals indicate about their formation?

<p>It reflects the latitude where the rocks crystallized. (D)</p> Signup and view all the answers

What conclusion can be drawn from discrepancies between ancient rocks’ magnetic directions and present magnetic pole positions?

<p>Continents have shifted from their original positions. (C)</p> Signup and view all the answers

Which statement accurately describes the study of paleomagnetism?

<p>It examines the historical magnetic properties of rocks to infer continental movements. (C)</p> Signup and view all the answers

In paleomagnetism, a flat magnetic inclination in ancient basaltic lava suggests what about its formation?

<p>It indicates the lava cooled near the equator. (A)</p> Signup and view all the answers

How do magnetic iron-bearing minerals behave as they crystallize from molten lava?

<p>They align with the Earth's magnetic field. (C)</p> Signup and view all the answers

What information can be determined from rock samples containing magnetic minerals?

<p>The historical geographic distribution of continents. (A)</p> Signup and view all the answers

What does the term 'polar wandering curves' refer to in the context of paleomagnetism?

<p>The movement of continents relative to the magnetic poles. (C)</p> Signup and view all the answers

What does evidence from paleomagnetism primarily support regarding the theory of continental drift?

<p>All continents were once a part of a single landmass. (D)</p> Signup and view all the answers

What was the main proposal made by Alfred Wegener regarding continental drift?

<p>A super-continent Pangea split into smaller fragments. (D)</p> Signup and view all the answers

What was a major critique of Wegener's theory of continental drift?

<p>There was no satisfactory mechanism for continental movement. (C)</p> Signup and view all the answers

Which evidence supported Wegener's idea that Africa and South America were once joined?

<p>Similar rock types and ages across both continents. (C)</p> Signup and view all the answers

How did the distribution of ice and tundra areas challenge the understanding of continental positions?

<p>They indicated that these areas were once closer to the equator. (A)</p> Signup and view all the answers

What is the prevailing mechanism that explains the movement of tectonic plates?

<p>Convection currents in the mantle. (B)</p> Signup and view all the answers

What phenomenon is primarily responsible for the creation of new oceanic crust?

<p>Sea-floor spreading. (A)</p> Signup and view all the answers

What type of rock evidence supported Wegener's theory in terms of mountain ranges?

<p>Similar rock types and ages in the Appalachians and Caledonides. (B)</p> Signup and view all the answers

What did Wegener believe about the continents in relation to oceanic crust?

<p>Continents drift over a denser oceanic crust. (D)</p> Signup and view all the answers

Flashcards

Continental Drift

The hypothesis that the continents were once joined and have since moved to their current positions.

Pangea

A supercontinent that existed millions of years ago, including all the current continents.

Fossil Evidence

Similar fossils found on different continents, suggesting past connections.

Mesosaurus

A reptile whose fossils are found on both sides of the Atlantic.

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Wegener's Hypothesis

The idea that continents have moved over millions of years.

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Inferred Latitudes

Determining the past positions of ancient rocks based on clues.

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Scientific Method

A process of gathering data, forming hypotheses, testing them, and refining the hypotheses to become theories.

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Laurasia/Gondwanaland

Two major landmasses that formed from the breakup of Pangea.

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Paleomagnetism

The study of the magnetic properties of old rocks.

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Magnetic Inclination

The angle at which a magnetic field dips relative to the horizontal.

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Magnetic Pole

The point on Earth's surface where the magnetic field is most concentrated.

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Polar Wandering Curves

Graphs showing the apparent movement of Earth's magnetic pole through time.

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Magnetite

A common iron-bearing mineral that preserves magnetic information.

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Lava

Molten rock that cools and solidifies.

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Magnetic Direction

Indicates the orientation of the magnetic field.

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What did Wegener propose?

Alfred Wegener proposed the theory of Continental Drift, suggesting that a large supercontinent called Pangaea split into smaller fragments about 200-300 million years ago, which then drifted apart to form the present arrangement of continents.

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Wegener's Evidence

Wegener's theory was based on several pieces of evidence, including the fit of continents, similar rock types and ages on different continents, distribution of fossils, and glacial patterns that suggested past connections.

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Fit of Continents

Matching the coastlines of continents, especially Africa and South America, suggested a potential past connection. This fit improved when considering the continental slope, which is the underwater boundary of the continent.

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Similar Rock Types

Similar rock types and ages found on different continents, like the Appalachians and Caledonides, supported the idea that these continents were once connected.

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Fossil Distribution

Similar fossils, such as the reptile Mesosaurus, found on different continents separated by oceans suggest these continents were once close together.

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Glacial Patterns

Ancient glacial patterns suggested that ice sheets once covered areas that are now in different latitudes. This challenged the idea that earth's orientation has remained constant.

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Why was Wegener's theory not accepted?

Wegener's theory was not widely accepted because he couldn't explain how continents moved. He suggested continents 'floated' over the denser oceanic crust, but this explanation was unsatisfactory.

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Sea-Floor Spreading

The discovery of sea-floor spreading, a process by which new oceanic crust is continuously formed at mid-ocean ridges, provided the missing mechanism for Continental Drift.

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Study Notes

Book Problem

  • Course title: Dynamic Earth
  • Course number: Geology 105
  • Instructor: Professor Rhodes
  • University: UMASS AMHERST
  • Department: Geosciences

Chiapas Earthquake, Mexico

  • Date: Sept 7, 2017
  • Magnitude: M = 8
  • USGS ShakeMap: Offshore Chiapas, Mexico
  • Depth: 697 km
  • Time: 04:49 UTC

Office Hours

  • Mike Rhodes: Tuesday and Thursday 3:00 - 5:00 pm
  • Sumaya Hamdi, TA: Wednesday 9:30 - 11:30 am; Tuesday and Thursday 1:00 - 2:00 pm

Theory of Continental Drift

  • Alfred Wegener (1912): Proposed that a supercontinent, Pangea, split into smaller fragments 200-300 million years ago. These fragments drifted apart to form the current continents.
  • Lack of a convincing mechanism: Wegener lacked a satisfactory explanation for how the continents moved. He suggested they "floated" over the denser oceanic crust, like icebergs.
  • Limited acceptance: Most geologists were skeptical and the theory wasn't widely accepted.

Fit of Continents

  • Matching continental shapes: Early attempts to fit continents together, particularly South America and Africa, were not precise using just shorelines.
  • Improved fit with continental slopes: A better fit was achieved by considering the continental slope and an increase of depth to about 2000 meters.

Similar Rock Types Across Continents

  • Matching rock formations: Geological formations and rock types, like the Appalachians and Caledonides, are similar on continents that would fit together.
  • Similar ages: The rocks that are matched have also similar ages.

Distribution of Ice

  • Past ice ages: Ice sheets covered areas that are now far from the poles, suggesting different continental positions in the past.
  • Orientation issue: If the earth's orientation relative to the sun has remained constant, these glaciated areas are in the wrong latitudes, too far north.

Fossil Distribution

  • Mesosaurus: This reptile lived about 250 million years ago and its fossils are found on both sides of the Atlantic in South America and Africa.
  • Other reptiles and plants: Similar fossils of reptiles and plants are found in different continents, supporting that the continents were once connected.
  • Implication: How could these organisms cross the oceans? They couldn't. So, the landmasses where they lived were once joined.

Continental Movement Over Time

  • Pangea breakup: Wegener's theory depicted how Pangea broke apart into different landmasses over millions of years.
  • Various timeframes: 225 million years ago, 135 million years ago, 65 million years ago the positions on the earth were quite different.

Arguments Favoring Continental Drift

  • Fit of continents
  • Rock similarities on different continents
  • Fossil similarities on different continents
  • Similar ancient climates on different continents
  • Paleoclimatic evidence
  • Apparent polar wanderer curves:
  • Ice and Glacial movements: Past glacial periods on different continents

Scientific Method

  • Gather data: Observe and make measurements.
  • Formulate a hypothesis: Develop a testable explanation.
  • Test the hypothesis: Collect more data and try to disprove it.
  • Refine or reject the hypothesis: If the hypothesis survives testing, refine it.
  • Develop a theory: After repeated testing, a hypothesis can become a theory.

Paleomagnetism

  • Study of Earth's magnetic properties: The study of magnetic properties of rocks, indicating their position relative to the Earth's magnetic poles at the time of formation.
  • Magnetic direction and inclination: Rocks show information about the direction and inclination of the magnetic field where they were formed and cooled.
  • Magnetic polarity: The poles of rocks may not correspond to the current position of the Earth's magnetic poles, because the continents may have moved.
  • Apparent polar wandering: The movement of magnetic poles.

"Polar Wandering" Curves

  • Mismatched ancient poles: Ancient rocks don't correspond with current magnetic pole positions. The continents were in a different configuration in the past.
  • Continents’ movement: Not the magnetic poles that move. It is the continents that move.

Conclusion

  • Paleomagnetism supports continental drift.
  • Continents were connected.
  • Continents have moved.

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Related Documents

Lecture 3 Continental Drift PDF

Description

Explore the significant Chiapas Earthquake of 2017 and the theory of continental drift by Alfred Wegener. This quiz will evaluate your understanding of geological processes and the historical context of continental movement. Prepare to analyze key concepts and data related to Earth dynamics.

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