Untitled Quiz

MARINE ENVIRONMENT

• Oceanography Geology is the subject matter

Sub-topics

• Earth internal structure
• Plate tectonic
• Seafloor features
• Marine sediments

Internal Structure of the Earth

• External shape of the Earth

• Internal structure and various layers

• Crust, Mantle, Core

• Discontinuities (e.g. Moho, Gutenberg, Lehmann)

• Evidence of Earth's interior structure

• Earth is not a perfect sphere, but an oblate ellipsoid

• Equatorial diameter is greater than polar diameter due to rotation

• The Earth's diameter at the equator is 12,756 km

• The Earth's diameter at the poles is 12,714 km

• Layers:

• Crust (Outermost layer; very thin and rigid; Continental – granite, Oceanic - basalt)

• Mantle (partially molten; less dense than core)

• 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

• Measurement of ocean depths

• Also includes charting of ocean floor shapes

• Methods used to determine ocean floor characteristics

• History (Lead and line sounding)

• Modern methods (Echo sounding, sonar, satellite-based radar, submersible surveys, ship-based seismic reflection)