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What concept did Alfred Wegener develop to describe the original state of all continents being joined?
Which of the following does NOT represent evidence for continental drift?
What was Alfred Wegener's academic background?
What mechanism is suggested to help separate continental masses according to the document?
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What geological feature is mentioned as common in areas of continental rifting?
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What is the typical geothermal gradient for non-active geothermal areas?
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What was one of the findings Wegener discovered in 1911 that contributed to his continental drift theory?
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Which equation represents the calculation of the geothermal gradient?
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Which continents were noted to have shared terrestrial fossils of the Permian age?
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How much movement along major fault zones was indicated in some places?
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What is classified as an abnormal geothermal gradient?
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Who proposed the concept of continental drift?
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What critical theory builds upon continental drift concepts?
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How did early geologists prove continental drift?
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What aspect of Earth's lithosphere does plate tectonics primarily describe?
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Which of the following movements are included within continental drift?
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What percentage of Earth's volume is attributed to the mantle?
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Which type of rocks primarily composes the oceanic crust?
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What is the predominant material found in the inner core of the Earth?
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What is one reason why the inner core remains solid despite high temperatures?
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Which statement is true about the continental crust compared to the oceanic crust?
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What depth does the mantle extend to?
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What primarily determines the composition of the lower continental crust?
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What is the range of thickness for the continental crust?
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What phenomenon occurs when magnetite crystallizes from magma?
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What type of continental margin is formed when two continental plates collide?
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What drives the process of seafloor spreading?
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What is the primary material involved in the formation of most oceanic crust?
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During divergent activity, new oceanic crust is created from?
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How do we determine the historical direction of magnetic north from rock formations?
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What happens at convergent oceanic-continental margins?
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What is the typical spreading rate for oceanic ridges in the Atlantic?
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Study Notes
Earth Structure
- Earth is composed of three main layers: crust, mantle, and core.
- The core accounts for nearly half of Earth's radius but only 16.1% of its volume.
- The mantle comprises the majority of Earth's volume (82.5%), with the crust making up a mere 1.4%.
Crust
- The crust represents the outermost layer, with a thickness ranging from 5 to 70 km.
- Continental crust is thicker and less dense than oceanic crust, consisting primarily of felsic rocks like granite.
- Oceanic crust, thinner and denser, underlies ocean basins and is composed of mafic rocks, rich in iron and magnesium, like basalt.
Mantle
- Extends to a depth of 2,890 km, composed of silicate rocks richer in iron and magnesium than the crust.
- Has a specific gravity of 4.5-5.0 and is near its melting point, allowing it to flow under stress.
- Movements within the mantle drive volcanic activity and crustal deformation.
Core
- Extends to a depth of 7,000 km, consisting of a liquid outer core (radius of 2,400 km) and a solid inner core (radius of 1,220 km).
- Primarily composed of iron and nickel.
- The inner core is solid due to immense pressure despite temperatures comparable to the Sun's surface.
- Recent studies suggest the inner core might be composed of plasma with the density of a solid.
Earth's Temperature Gradient (Geothermal Gradient)
- The rate of temperature increase with depth, usually constant at 3°C per 100 meters for non-active geothermal areas.
- In active geothermal areas, this gradient increases dramatically on a nonlinear scale.
- Equation to calculate geothermal gradient: GG = (T2 - T1)/ (D2 - D1) where T1 and T2 are surface and subsurface temperatures, and D1 and D2 are corresponding depths.
Plate Tectonics and Continental Drift
- Plate tectonics theory describes the large-scale movements of Earth's lithosphere.
- It builds upon the concept of continental drift, which proposes that continents drift across the ocean floor.
- The theory was widely accepted after concepts of seafloor spreading were developed in the late 1950s and early 1960s.
Continental Drift
- It refers to the movement of Earth's continents relative to each other, appearing to drift across the ocean bed.
- Alfred Wegener proposed this theory in the early 20th century, based on matching Permian-aged terrestrial fossils found on different continents.
- He coined the term Pangea for the supercontinent that included all present-day continents.
Causes of Continental Drift
- Convection currents in the mantle, driven by heat, provide a mechanism for separating continental masses from a spreading center.
- Light-weight crustal materials floating on denser lithosphere and mantle might also respond to Earth's rotation and move across its surface.
Evidence for Continental Drift
- Structural trends extending across continents end abruptly at coasts and reappear on facing continents across oceans.
- Direct measurements along major fault zones indicate movements of up to 6 cm per year.
- Similarities in rock types, fauna, and flora between the eastern coast of South America and western coast of Africa.
- Polar Wandering curve (Paleomagnetism) shows magnetized minerals with different orientations from the current polar N-S curve.
Paleomagnetism
- When magnetite crystals form from magma, they become magnetized parallel to Earth's magnetic field at that time.
- Rocks like basalt, with high magnetite content, preserve this remnant magnetism.
- Studying the horizontal and vertical components of this magnetism reveals the direction to magnetic north and the latitude at the time of the rock's formation.
Types of Continental Margin Movement
- Convergent margins: Occur when continents collide, forming mountain ranges like the Alps and Himalayas.
- When a continental and oceanic plate collide, the continental plate overrides the oceanic plate.
- Divergent margins: Occur when plates break apart along a spreading center and move away from each other.
- New oceanic crust is created from magma rising from the mantle at these boundaries.
Seafloor Spreading
- The process of new crust formation between two plates moving apart.
- Molten rock rises from the Earth's interior at oceanic ridges, adding new seafloor to the edges of the old seafloor.
- As the seafloor widens, continents on opposite sides of the ridges move away from each other.
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Description
This quiz explores Earth's three main layers: crust, mantle, and core. Understand their composition, characteristics, and role in geological processes. Test your knowledge on the thickness and density variations within these layers.
