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Questions and Answers
What is the primary rock type that makes up the oceanic crust?
What is the primary rock type that makes up the oceanic crust?
Which layer of the Earth is directly below the crust?
Which layer of the Earth is directly below the crust?
What is the primary characteristic of continental crust compared to oceanic crust?
What is the primary characteristic of continental crust compared to oceanic crust?
What is the Moho Discontinuity?
What is the Moho Discontinuity?
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How thick is the oceanic crust on average?
How thick is the oceanic crust on average?
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Which part of the Earth does the lithosphere include?
Which part of the Earth does the lithosphere include?
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What percentage of Earth's total volume is made up by the mantle?
What percentage of Earth's total volume is made up by the mantle?
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What is the primary rock type found in continental crust?
What is the primary rock type found in continental crust?
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What is the primary composition of the Earth's oceanic crust?
What is the primary composition of the Earth's oceanic crust?
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Which of the following layers does not make up the Earth's interior structure?
Which of the following layers does not make up the Earth's interior structure?
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How does the thickness of the continental crust generally compare to the oceanic crust?
How does the thickness of the continental crust generally compare to the oceanic crust?
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What percentage of Earth's volume does the crust occupy?
What percentage of Earth's volume does the crust occupy?
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Which element is more prevalent in the crust compared to the mantle?
Which element is more prevalent in the crust compared to the mantle?
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What classification is used to define the outermost shell of a rocky planet like Earth?
What classification is used to define the outermost shell of a rocky planet like Earth?
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What is true about the relationship between the crust and the mantle underneath it?
What is true about the relationship between the crust and the mantle underneath it?
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What is the primary process responsible for the formation of Earth's crust?
What is the primary process responsible for the formation of Earth's crust?
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What is the primary composition of the continental crust?
What is the primary composition of the continental crust?
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Which layer of the Earth is described as the outermost layer?
Which layer of the Earth is described as the outermost layer?
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Which characteristic accurately describes the oceanic crust?
Which characteristic accurately describes the oceanic crust?
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What is the density of the continental crust?
What is the density of the continental crust?
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What material primarily composes the upper mantle?
What material primarily composes the upper mantle?
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The outer core is characterized as being what state of matter?
The outer core is characterized as being what state of matter?
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How did Earth's layers initially form?
How did Earth's layers initially form?
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Which layer is less dense than the core?
Which layer is less dense than the core?
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Study Notes
MARINE ENVIRONMENT
- Oceanography Geology is the subject matter
Sub-topics
- Earth internal structure
- Plate tectonic
- Seafloor features
- Marine sediments
Internal Structure of the Earth
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External shape of the Earth
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Internal structure and various layers
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Crust, Mantle, Core
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Discontinuities (e.g. Moho, Gutenberg, Lehmann)
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Evidence of Earth's interior structure
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Earth is not a perfect sphere, but an oblate ellipsoid
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Equatorial diameter is greater than polar diameter due to rotation
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The Earth's diameter at the equator is 12,756 km
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The Earth's diameter at the poles is 12,714 km
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Layers:
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Crust (Outermost layer; very thin and rigid; Continental – granite, Oceanic - basalt)
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Mantle (partially molten; less dense than core)
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Core (dense; Iron and Nickel; Inner Core - solid; Outer Core - liquid)
Formation of Earth's Layers
- The Earth formed through accretion, absorbing planetesimals (lumps of rock and ice?)
- Earth may have accreted undifferentiated material that later separated and formed layers
- Core formation may have happened before the shell, or a combination of previous planetesimals.
- The formation of the Earth's layers was due to accretion of undifferentiated bodies
Internal Structure of the Earth (Diagram)
- The Interior structure of the Earth is layered in spherical shells
- Earth can be chemically divided into 5 layers (Crust, Upper Mantle, Lower Mantle, Outer Core, and Inner Core)
- Crust
- The outermost solid shell
- Chemically distinct from mantle
- Richer in incompatible elements than mantle
- Oceanic ~ 5-10 km; Continental ~30-70 km
- Mantle
- Lies between the outer core and crust
- Average thickness of 2,800 km
- Makes up 84% of the Earth's volume
- Solid, but behaves as a viscous fluid in geological time
- Upper and Lower mantle
- Core
- Liquid outer core, and solid inner core
- Located at approximately 2,880 km beneath the Earth's surface (outer core-mantle boundary).
- Approx 5155 km beneath the planet's surface, marks the boundary between the inner and outer core.
Moho Discontinuity
- Boundary between Earth's crust and mantle
- Defined by contrast in seismic velocity
- Oceanic crust lies ~5-10 km beneath the ocean floor
- Continental crust lies ~20-90 km beneath the continents
- Moho falls within the Lithosphere
Lithosphere and Asthenosphere
- Lithosphere: rigid outer part of Earth.
- Includes crust and part of upper mantle
- Asthenosphere: highly viscous, mechanically weak upper layer of Earth's mantle
Gutenberg Discontinuity
- Core-mantle boundary of Earth
- Located approximately 2880 km beneath the Earth's surface
Lehmann Discontinuity
- Separates the liquid outer core from the solid inner core.
- Shows abrupt increases in P-wave and S-wave velocities.
Density (p) of Earth's Layers
- Density increases from ~2.7 g/cm³ in the upper crust to ~12 g/cm³ in the inner core.
Behavior of Earth's Layers
- SiMA (lower layer of Earth's crust) – rich in magnesium silicate
- SIAL (upper layer of Earth's continental crust) – rich in silicates and aluminum
- Core rich in nickel (Ni) and iron (Fe)
Seismic Waves through the Earth
- Seismology studies earthquakes and elastic waves to understand Earth's structure.
- Primary (P) waves and secondary (S) waves are used in the study of how different materials affect the distribution of seismic waves
Isostasy
- State of gravitational equilibrium between Earth's crust and mantle.
- Adjacent rocks float on the plastic mantle.
- Thicker blocks extend deeper into the mantle.
- Oceanic crust is heavier, but less thick, than continental crust
Convection Currents
- Caused by hot material rising and cooling and sinking in the mantle
- Circular motion in the asthenosphere that affects the crust
- Similar to hot water in a pan
Plate Tectonics
- Plate tectonics is a theory that explains the large-scale motions of Earth's lithosphere
- The Earth's crust and upper mantle are broken up into numerous sections called tectonic plates.
- Plate sections are rafts, moving around on mantle
Continental Drift
- The movement of continents over time
- Evidence includes similar fossils, matching coastlines.
Seafloor Spreading
- New oceanic crust is formed at mid-ocean ridges.
- It explains continental drift in plate tectonics theory
Transform Plate Boundaries
- Plates slide horizontally past each other.
- No crust is created or destroyed
- San Andreas Fault in California is an example
- There are no volcanoes at transform boundaries
Three Basic Types of Plate Boundaries
- Divergent – plates move apart
- Convergent – plates move together
- Transform – plates move past each other
Convergent Plate Boundaries
- Oceanic-oceanic
- Heavier plate subducts beneath the lighter plate, forms volcanoes.
- Oceanic-continental -Denser oceanic plate subducts, forms volcanoes
- Continental-continental -Compressing or sliding, creating mountain ranges.
Major/Minor/Micro Plates
- Seven major plates (area > 10 million km²):
- Pacific Plate, North American Plate, Eurasian Plate,
- African Plate, Antarctic Plate, Indo-Australian Plate and South American Plate.
- More than 9 minor plates (area > 1 million km²): Nazca Plate, South China Sea Plate,
- Philippine Sea Plate, Arabian Plate, Caribbean Plate, Cocos Plate,
- Caroline Plate, Scotia Plate, Burma Plate, and New Hebrides Plate.
- About 60 micro-plates (<1 million km²)
Sea Floor
- The ocean floor is highly varied, features include mountains, valleys, plains, plateaus in the ocean floor.
Divisions of the Marine Environment
- Shallow margin – littoral and neritic
- Deep sea = pelagic
Marine Sediments
- History
- Source and composition
- Distribution (neritic and pelagic)
- Formation :
- Sources
- Terrigenous/lithogenous: Erosion off land (rivers, wind); Volcanic eruptions
- Biogenous: Shells, skeletons, marine organisms
- Hydrogenous: Precipitates from seawater
- Cosmogenous: Space dust, meteorites
- Amounts of deposits from various sources
- Compositional type (Terrigenous/Lithogenous, Biogenous, Hydrogenous, and Cosmogenous)
- Indicators of sediments
- Distribution of sediment (Neritic and pelagic)
Bathymetry
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Measurement of ocean depths
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Also includes charting of ocean floor shapes
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Methods used to determine ocean floor characteristics
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History (Lead and line sounding)
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Modern methods (Echo sounding, sonar, satellite-based radar, submersible surveys, ship-based seismic reflection)
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