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Chapter 3: Drifting Continents and Spreading Seas

Geotours

Download Geotours.

Getting Started :

If you haven’t done it already, download Google Earth™ and install it on your computer.
If you haven’t done it already, download the Geotours.kmz file and save a copy to your desktop. (The Geotours.kmz file contains the Geotours for all chapters, so you only need to download this once!)
By downloading Geotours.kmz you acknowledge that it was created solely to accompany Steve Marshak's Earth: Portrait of a Planet and Essentials of Geology and is limited to use with only Steve Marshak's Earth: Portrait of a Planet and Essentials of Geology and may not be reproduced, stored in a retrieval system, or transmitted in any form by any means for any other purpose without the written permission of the publisher.
Double-click the Geotours.kmz file and Google Earth™ will open automatically.
In the left-hand sidebar you will see a Places menu, and in the Temporary Places folder you will see an EARTH_3e.kmz file. Double-click the file and you will see a list of Geotours for each chapter.
Then open the Geotour folder you want to explore! If you’d like to read more about the features of Geotours see Using Geotours, or go to our Helpful Resources section.

STOPS ON GEOTOUR 3: Wegener's Evidence

Matching Coastlines

See also Worksheet Problems 1-2

The Scotia Arc

See also Worksheet Problem 3
"What a Geologist Sees" Geofeatures: South Sandwich Trench, Volcanic Arc, Mid-Ocean Ridge, and three Transform Faults

GEOTOUR 3 WORKSHEET

Alfred Wegener suggested that features visible on a map of the Earth's surface supported the concept of continental drift. He recognized the "fit of the continents" and he found landforms whose shape seemed to be the result of continental movement.

1. Two points that are now on opposite sides of an ocean, but were once adjacent before drift occurred and the ocean formed, are called conjugate points.

(a) Look at Image G3.1. Turn on “Populated Places” in the Layers panel and locate the city of Natal (Brazil; see the placemark labeled Problem 1a). This city lies near the easternmost point on the coast of South America. What geographic feature occurs on the conjugate coast of Africa?

(b) What is the distance (in km) between these two conjugate points (use the Measuring Tool)?

(c) For reasons discussed in Chapter 4, geologists determined that these points were adjacent about 90 million years ago. At what rate did Natal drift away from the conjugate point in Africa? Express your answer in centimeters per year. (Hint: The calculation involves the equation: rate = distance/time.)

(d) Not only did Wegener recognize points on conjugate shorelines, but he also noticed that generally a more accurate match of continental margins can be obtained by comparing the edges of continental shelves. Examine Image G3.3. What is the separation between the continental shelves of Australia and Antarctica (in km; see placemarks labeled Problem 1d).

(a) What is the present-day diameter of the crater (km)?

(e) In what direction did Australia drift, relative to Antarctica, to reach its present location? (Hint: The direction is parallel to the line connecting conjugate points.) Note that this direction is parallel to prominent cracks on the ocean floor between the two continents. These cracks, as discussed in Chapter 4, are called fracture zones.

2. Fly to the placemark labeled Problem 2. This point lies at the intersection of three features: the Red Sea (a narrow ocean), the Gulf of Aden (a narrow ocean), and the East African Rift (the belt that is in the process of splitting Africa in two). The Arabian Peninsula is the area of land east of the Red Sea and north of the Gulf of Aden.

(a) The Red Sea and the Gulf of Aden are opening at approximately the same rate. In which compass direction is the Arabian Peninsula drifting, relative to Africa?

(b) Because of its motion, the north end of the Arabian Peninsula is pushing into Turkey. Which of the following features is forming as a consequence (choose one)? (Hint: You may want to turn on the “Border” option in the Layers panel to find Turkey, and you may need to adjust your location and elevation to see the feature.)
- a belt of mountains
- a vast jungle
- a broad plain

(c) Turn on “Geographic Features” in the Layers panel. The line of volcanoes defines the trace of the East African Rift, as discussed in Chapters 4 and 6. If rifting succeeds and a new ocean develops along the trace of the East African rift, in which compass direction will the region east of the rift move, relative to the rest of Africa? (Hint: Assume that the motion is perpendicular to the line of volcanoes.)

The Scotia Arc

3. Fly to the placemark labeled Problem 3 on the east coast of southern South America.

(a) What is the distance between this point and the conjugate point on the margin of southern Africa? (Hint: Use the trend of the fracture zones in the South Atlantic to help you find the conjugate point on the African coast. Note that your measuring line passes through Placemark 3 on the Mid-Atlantic Ridge.)

(b) Considering the difference between your answers for Problems 1b and 3a, did South America rotate clockwise or counterclockwise, relative to Africa, as drift occurred?

(c) Wegener speculated that the curving traces of southern South America and the Antarctic Peninsula indicated that these land masses were once aligned with the Scotia Arc, and subsequently moved relative to the Scotia Arc, dragging and bending as they slid sideways past the intervening tongue of ocean. In which direction did the Antarctica and South America move, relative to the Scotia Arc?

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StudySpace: Chemistry 2e.