Plate Tectonics and Continental Drift

During a school project on historical scientific theories, Aiden became fascinated with the fossil evidence that Wegener used to support his hypothesis of continental drift. How did fossils demonstrate that the continents were once connected?

• Animal fossils such as the mesosaurus were found on one continent.

• Scientists found examples of different kinds of fossils on some continents.

• Plant fossils of the same kind of fernlike plants were found on five continents.

• Freshwater animal fossils were found in the nearby oceans.

Answer explanation

Plant fossils of the same kind of fernlike plants were found on five continents, indicating they were once connected.

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After studying plate tectonics, Lee became interested in mid-ocean ridges and how rock develops as the tectonic plates spread apart, so he decided to investigate further. Which of the following statements are true about sea-floor spreading? Choose the three statements that apply.

• Young rock forms in layers on the ocean floor as spreading occurs.

• Magma flows through cracks in Earth’s crust and hardens.

• Continental crust is formed by the ridges as they grow.

• Mid-ocean ridges are the sources of the spreading.

• Older rock is farther away from the mid-ocean ridges.

Answer explanation

Answer Explanation highlighting the correct choices

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Imagine a science project by students Benjamin, Isla, and Nora, where they create a small-scale model of the Earth's crust to demonstrate the theory of plate tectonics. In their model, they show how the Earth's crust is divided into twelve large plates that float on a layer of hotter, softer rocks, simulating the mantle. These plates move very slowly, just centimeters each year, but even these minor movements can lead to significant natural phenomena. What is the source of energy that drives the movement of these plates in their model?

• convection currents in the mantle

• subduction zones at plate boundaries

• the friction force between plates

• different densities between the oceanic and crustal plates

Answer explanation

Convection currents in the mantle are the source of energy that drives the movement of the plates in the model, as they cause the plates to slowly move due to the heat transfer within the Earth's interior.

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Which statement provides the best additional evidence supporting the scientific conclusion that continents were once joined, but have drifted apart over time?

• Most glaciers found around the North Pole have edges that seem to align with glaciers at the South Pole.

• Ancient animal species have migrated from one continent to another via an extensive intercontinental land bridge.

• The sequence of rock layers on Africa’s western coast is almost identical to those found on South America’s eastern coast.

• Similar plants alive today are found in Africa, North America, South America, and Asia.

Answer explanation

The sequence of rock layers on Africa’s western coast is almost identical to those found on South America’s eastern coast, providing strong evidence of continental drift.

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What factor contributes to the presence of numerous marsupial mammal species in both Australia and South America, considering that these two continents were formerly connected?

• Continental drift

• The first mass extinction

• The fifth mass extinction

• Ozone production

Answer explanation

Continental drift is the factor that contributes to the presence of numerous marsupial mammal species in both Australia and South America, as these two continents were formerly connected.

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In the diagram of the ocean basin, where is the oldest oceanic crust found?

• A

• B

• C

• D

Answer explanation

The oldest oceanic crust is found at location D in the diagram of the ocean basin.

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During a geography lesson, Derrick learned that the convection cycles of the mantle are the main cause of movement of what part of the Earth?

• inner core

• crust

• oceans

• atmosphere

Answer explanation

The convection cycles of the mantle cause movement of the crust, making it the main part of the Earth affected by this process.

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Ocean trenches are most often formed when ______.

• an oceanic plate is forced underneath a continental plate.

• two oceanic plates grind past each other along transform faults.

• two oceanic plates hit each other causing both plates to rise up.

• two continental plates slide past each other.

Answer explanation

Ocean trenches are most often formed when an oceanic plate is forced underneath a continental plate, leading to subduction.

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Seafloor spreading is a geological phenomenon observed at mid-oceanic ridges, where tectonic plates diverge. As volcanic activity generates new crust at these ridges, it moves away from the ridge axis, displacing the existing crust laterally and causing the seafloor to expand.

Seafloor spreading is one reason ______.

• mid-ocean ridges are small mountain ranges.

• all earthquakes have their epicenters in oceans.

• most active volcanoes are found in the Atlantic Ocean.

• the continents are drifting apart.

Answer explanation

Seafloor spreading causes the continents to drift apart as new crust is generated at mid-oceanic ridges, pushing the existing crust laterally and expanding the seafloor.

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Plate tectonics is the scientific theory describing the large-scale motion of large plates and the movements of a number of smaller plates of the Earth's surface.

• True

• False

Answer explanation

Plate tectonics is indeed the scientific theory describing the large-scale motion of Earth's plates, making the answer True.

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