3: The Earth & Plate Tectonics Flashcards
Explain the Crust, Mantle, and Core in more detail:
Crust: 6-50km
- oceanic crust (more dense, less thick, younger)
- Continental (less dense, thicker, older)
- LITHOSPHERE SHARED WITH MANTLE
Mantle: 2900km
- Lithosphere
- Asthenosphere
- Central/lower mantle
Core: 3400km
- Outer core (liquid due to temperature)
- Inner core (solid due to pressure). Up to 6000 C!
What is the difference between P waves and S waves? How are they formed?
P waves (primary waves):
- compression wave
- travel through solid and liquid
S waves (secondary waves):
- Shear wave
- travel through solid only
Earthquakes generate both of them
If a Earthquake would happen in the north pole, what observations would be made on other parts of the earth?
P-Waves:
- P-waves would be felt on the south pole, but there would be a region of darkness
S-Waves:
- they would only reach about halfway around the earth and nothing in the south pole!
What is the source of earth’s protective shield?
The earth’s core consists of a fluid outer core and solid inner core.
Because the outer core contains iron, it generates a magnetic field when it flows, aka, Earth’s protective shield!
What is the supercontinent called? What proof was there for it?
Pangea
- The continents fit like a jigsaw puzzle
- The alignment of geologic feature and similar rock types/ages
- The alignment of fossil finds
- The Alignment of paleo-climates (past climates)
What is Seafloor spreading & Continental Drift?
- Continents are moved by the generation of new crust at the mid-oceanic ridges
- Sometimes, continents are split by the formation of spreading ridges
- As plates split, they must push against other plates and the denser one (oceanic) subducts
What is the modern theory of Plate Tectonics?
The Earth’s surface is separated into plates which are moving with different velocities (speed and direction are different)
These differences in plate motion cause transform, divergent, and convergent boundaries at plates.
What is the lithosphere and asthenosphere?
Lithosphere: The earth’s rigid outer shell (crust, upper mantle)
Asthenosphere: Weak part of the upper mantle that behaves like a viscous solid (plastic, play-doh-like)
Elaborate more on divergent plate boundaries:
Mostly mid-ocean ridges (sea floor spreading)
- Can also be found when continents break apart
- Produced by extensional forces acting on the lithospheric plates
- as oceanic moves away from ridge, it cools and becomes denser
Elaborate more on transform plate boundaries:
Plates slide past each other
- Typically connect mid-ocean ridge segments
- Sometimes they may cut through continental crust (San Andreas Fault)
- No production/destruction of material
Elaborate more on Convergent Plate Boundaries:
Plates collide and one sinks beneath the other
- high frequency of earthquakes,
- may be marked by oceanic trenches of subduction zones
3 scenarios:
Ocean-Continent
Ocean-Ocean
Continent-Continent
What happens at ocean-continent subduction zones?
Older portions of the oceanic plates are subducted
As oceanic lithosphere/plate descends, partial melting of the mantle rock generate magma having a felsic (silica-rich) composition
- Mountains produced in part by volcanic activity associated with subduction
(density of melted rock <
density of surrounding rock, so melt rises forming volcanic arc)
What happens at ocean-ocean subduction zones?
The older and colder plate subducts. The plate melts and the resulting magma is buoyant and floats toward surface, pushing up crust and forming volcanoes on ocean floor.
- IF volcanoes emerge as islands, volcanic island arc is formed (japan)
What happens at continent-continent subduction zones?
The less dense, buoyant continental lithosphere does not subduct well, resulting in a collision.
- results in uplift and thickening of continental crust (high mountains)
ex/ Himalayas, Alps)
