What is it called when Earth's magnetic poles change places?
answer
magnetic reversal
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used as evidence for sea-floor spreading
answer
magnetic reversal
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part of molten rock at mid-ocean ridges
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magnetic minerals
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hypothesis that states that the continents were once one large mass that broke apart
answer
continental drift
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Describe how the polarity of Earth's magnetic field is recorded in the sea-floor.
answer
As new crust forms at mid-ocean ridges, tiny grains of magnetic minerals align themselves according to the Earth's magnetic field. As the rock cools, the alignment of these grains becomes permanent and provides evidence of the polarity of the Earth's magnetic field at the time of their formation.
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What are mid-ocean ridges?
answer
Mid-ocean ridges are mountain ranges at the floor of the ocean. Sea-floor spreading occurs at mid-ocean ridges.
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List the evidence that Wegener used to support continental drift.
answer
The continents fit together like a puzzle, fossils are located in areas where animals could not survive, and minerals and mountains are located on the edges of the continents.
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Restate Wegener's hypothesis in your own words.
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Weneger's hypothesis states that the present day continents were all once part of a giant, single continent that broke apart. The continents then drifted into their present locations.
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What is the major evidence that sea-floor spreading creates new lithosphere? Explain your answer.
answer
Answers will vary. Sample answer: Molten rock at mid-ocean ridges has magnetized minerals that align with Earth's magnetic field. When the Earth's magnetic field reverses, the magnetized minerals align in the opposite direction. The record of magnetic reversals is carried away from each side of the spreading center of a mid-ocean ridge, showing that the molten rock is creating new lithosphere.
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If similar fossil collections are found on two continents, now widely separated, what is a possible explanation?
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One possible explanation is that at the time that the fossilized species lived, the two continents were part of a single landmass.
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How do fossils help prove that the continents move?
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Fossils of the same plant and animal species have been found on continents on different sides of the Atlantic Ocean.
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Describe the process of sea-floor spreading.
answer
New oceanic lithosphere forms during sea-floor spreading. Magma rises towards the surface and solidifies in the cooler upper regions. Then, as the tectonic plates move apart from each other at the mid-ocean ridges, new magma rises to fill the gap. As this new crust forms, older crust is pushed outward, away from the mid-ocean ridges.
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Explain how a mid-ocean ridge is formed.
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Two oceanic plates are drifting apart, the mantle seeps up and forms new lithospheric plates.
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What was Pangaea?
answer
the large landmass that later broke up to form two supercontinents and then fragmented further to form the six continents that exist today
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