Chapter 11 Review Questions

Why didn't scientists widely accept the theory of continental drift when Wegener originally proposed it? What further evidence might have strengthened his theory?

Wegener was a meteorologists, not a geolists.He couldn't explain how continents could drift.

What links some earthquakes with isostatic equilibrium? Where do such earthquakes occur?

a The additional weight will cause the crust to deflect downwards, while the removal of material causes the crust to deflect upwards. This is called isostatic rebound. a During an earthquake, the landmasses (continental or ocean basin) on either side of the involved fault do not move together.

What are Pangaea and Panthalassa?

1 In 1912, a German meteorologist and polar explorer named Alfred Wegener proposed what was at the time a starling idea. a He proposed that in the distant past all the Earth's continents had been a single giant continent . Wegener called this continental Pangaea. a Surrounding Pangaea, he said, was a single large ocean he called Panthalassa.

According to the theory of plate tectonics, what happens at a convergent boundary?

At a colliding or convergent boundary, two plates push together. Convergent boundaries are also called destructive boundaries because movements along these boundaries destroy crust.

What evidence supports the theory of seafloor spreading?

Evidence comes from the ocean-bottom sediment samples, radiometric dating, and magnetometer data.

What evidence did Alfred Wegener use to support the theory of continental drift?

In the 1600's, the first accurate world maps became available. People noticed that the continents apparently fittogether like jigsaw-puzzle pieces. This was the first evidence of continental drift. It was hundreds of years later that Wegener began to see further evidence from other sources. In 1855, the German scientist Edward Suess found fossils of the Glossopteris fern in South America, Africa, Australia, India, and Antarctica. Continental drift proponents also studied the distribution of animals and fossils. Wegener also saw the distribution of coal as evidence.

According to the theory of the seafloor spreading, where and how does new crust form?

In the theory of seafloor spreading, new crust emerges from the rift valley in a mid-ocean ridge. Magma from the asthenosphere pushes up through the rift and solidifies into new crust. As more magma comes up from below, it pushes new crust away on each side of the ridge.

How do mid-ocean ridges, rift valleys and trenches relate to plate tectonic concepts?

Scientists estimate that the plate move a few centimeters a year, propelled by convection under the plate, pull from the subduction zones, and the force of magma pushing up between plates.

How did the invention of sonar contribute to information about the ocean bottom?

Sonar detects objects under water by transmitting a sound and receiving an echo. Based on the echo's angle, how long it took to return, and changes in frequency, sonar operators can determine where an object is, its distance, and whether it's moving

What two theories does the theory of plate tectonics unite?

The theories of continental drift and seafloor spreading.

According to the theory of plate tectonics, what does the lithosphere consist of?

The Earth's lithosphere consists of more than a dozen separate plates.

According to the theory of plate tectonics, what happens at a divergent boundary?

The crust pulls apart and forms valleys. Mid-ocean ridges and rift valleys mark divergent boundaries. Volcanic activity at a divergent boundary may build mountains higher than sea level.

How do scientists classify the Earth's internal layers?

The earth's interior consists of multiple layers: the inner core, the outer core, the mantle, and the crust.

What are mid-ocean ridges, rift valleys, and trenches?

The portion running through the middle of the Atlantic Ocean is called the Mid-Atlantic Ridge. Trenches are deep ravines in the seafloor. Rift valleys are deep valleys running through the center of the Mid-Atlantic Ridge and mid-ocean ridges.

How does the Earth's crust differ from the lithosphere?

a The inner core is thought to be made primarily of iron and nickel, with some silicon, sulfur, and other heavy elements present. a.Thought to have a temperature of 5000 degrees C (9032 degrees F) - nearly the same temperature as the surface of the sun. b. The inner core is theorized to be solid due to intense pressure.

What is isostatic equilibrium?

a The mantle is the layer above the core and is approximately 2,9000 kilometers (1,802 miles) in the thickness a.The mantle is thought to contain mostly silicon and oxygen with some iron and magnesium. Seismic wave studies have given scientists a picture of the mantle

What are the three types of rock? How does the rock cycle account for their formula?

a The outer core consists of the ssme elements at the same temperature. a. Scientists theorize that with less pressure, it is liquid.

How does Archimedes' Principle relate to the structure of the Earth?

a The radius of the total core is 3,470 kilometers (2,516 miles). In some places the outer core has thermal plumes, which are localized areas of high heat release that might possibly be related to volcanic activity.

What is the theory of continental drift?

a Wegener theorized that because the less dense continents floated on the molten rock of the mantle, Pangaea broke by floating apart into seperate pieces. The seperate continents reached their present locations by drifting apart for more than 200 million years. b.The theory that the continents were once a single land-mass thst drifted apart,