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?

They existed in a warm tropical climate that once covered those areas. Signup and view all the answers

What is the primary mechanism thought to drive continental drift?

Heat from the Earth's core causing mantle convection. Signup and view all the answers

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

Mountain ranges that do not match in geological age across continents. Signup and view all the answers

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

They were pushed by tectonic forces. Signup and view all the answers

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

Gathering further data to test existing hypotheses. Signup and view all the answers

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

It reflects the latitude where the rocks crystallized. Signup and view all the answers

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

Continents have shifted from their original positions. Signup and view all the answers

Which statement accurately describes the study of paleomagnetism?

It examines the historical magnetic properties of rocks to infer continental movements. Signup and view all the answers

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

It indicates the lava cooled near the equator. Signup and view all the answers

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

They align with the Earth's magnetic field. Signup and view all the answers

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

The historical geographic distribution of continents. Signup and view all the answers

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

The movement of continents relative to the magnetic poles. Signup and view all the answers

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

All continents were once a part of a single landmass. Signup and view all the answers

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

A super-continent Pangea split into smaller fragments. Signup and view all the answers

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

There was no satisfactory mechanism for continental movement. Signup and view all the answers

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

Similar rock types and ages across both continents. Signup and view all the answers

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

They indicated that these areas were once closer to the equator. Signup and view all the answers

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

Convection currents in the mantle. Signup and view all the answers

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

Sea-floor spreading. Signup and view all the answers

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

Similar rock types and ages in the Appalachians and Caledonides. Signup and view all the answers

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

Continents drift over a denser oceanic crust. Signup and view all the answers

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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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.