(8.4) Parts
-Inner Core
-Outer Core
-Lower Mantle
-Upper Mantle (Asthenosphere)
-Crust (Lithosphere)
(8.4)The Crust
-Thinnest layer
-Solid granodiorite
-Found as both oceanic + continental
(8.4) The Mantle
UPPER Mantle:
-State of matter: Mixed
-Solid peridotite that's close to its melting point
>Fe, Si, Mg (Iron, Silicon, Magnesium)
LOWER Mantle:
-State of matter: Mixed
-Solid peridotite that is more rigid, however due to its high temp, it's capable of grad
(8.4) The Core
OUTER Core:
-Liquid Fe and Ni (nickel)
-Generates Earth's magnetic field
INNER Core:
-Sold sphere of Fe and Ni
-High temperature, but it is a solid due to the immense pressure
(8.4) Types of Crust
CONTINENTAL:
-located on continents
-less dense
-very thick because of mountain ranges
OCEANIC:
-located at bottom of ocean
-more dense
-thinner crust
(8.4) Theory of Plate Tectonics State
-Earth's lithosphere is divided into sections called plates
-These plates move slowly overtime
-Movement results in many of Earth's physical features + events
-Tectonic plates "float" at the asthenosphere
>slush-like layer + semi-solid
(9.1) Alfred Wegener (1880-1930)
-In 1912, came up with the theory of Continental Drift
-Continental Drift Theory states that the continents were once connected as one large land mass and they slowly drifted to their current positions.
1) Wegener's Evidence
-Edges of the continents fit like puzzle pieces
Ex: South America + Africe
2) Wegener's Evidence
FOSSILS
-Mesosaurus (a fresh water/land animal) found in both South America + Africa
3) Wegener's Evidence
Rock Type Line Up
-Mountain ranges and mineral belts
-Similar rocks found in NJ and Scottish Highlands
4) Wegener's Evidence
PALEOCLIMATE (Glaciers)
-Evidence of Ice Sheets were found covering parts of South America, Africa, India, + Australia
-Coral reefs found in Northern Canada (coral reefs need warm water)
-Coal formation in North America
[Texas is the Oil State (Oil from a
Problems with Wegener's Theory
-Scientists did not accept his theory because he was missing key evidence (Such as: HOW DID THE CONTINENTS MOVE?)
RTN 9.1 Q1) What is the hypothesis of Continental Drift?
The continents had once been joined to form a single supercontinent, called Pangaea
RTN 9.1 Q3) Why did the scientists reject Wegener's continental drift hypothesis?
Wegener was not able to describe a mechanism that was able to move the continents. He said tidal waves could have been strong enough to move continents and that the continents/plates could break an ocean floor. Scientists proved him wrong saying that woul
RTN 9.1 Q4) What was Pangaea?
It was the super continent from 250 million years ago. Means "all land" in Greek.
(9.2) Ocean Floor
-WWII and the discovery of Sonar (Sound Navigation and Ranging)
-Mapped the ocean floor + found mountain ranges in the middle of the ocean
-Found trenches along the coastlines of the continents
(9.2) Harry Hess
-In 1968, Harry Hess came up with the theory of sea-floor spreading
-Theory explained all of the problems with Wegener's theory
-The Theory of Plate Tectonics was born
-The age of the oceanic crust gets progressively older further away from the Mid-Ocean
RTN 9.2 Q1) Describe mid-ocean ridge and deep ocean trenches.
DEEP-OCEAN TRENCHES: long , curvy valleys along the edges of some ocean basins
MID-OCEAN RIDGE: long chain of mountains extending the length of the ocean
RTN 9.2 Q2) Explain what occurs during sea-floor spreading.
New ocean floor forms along Earth's mid-ocean ridges, slowly moves outward across ocean basins, and finally sinks back into the mantle beneath the deep-ocean trenches
RTN 9.2 Q3) List evidence of sea-floor spreading
Evidence includes: - Magnetic stripes in ocean-floor
- Earthquake patterns
-Measurements of the ages of ocean floor rocks
RTN 9.2 Q4) What is a Wadati-Benioff Zone?
Many subduction zones cause eathquakes
-Pattern of earthquakes in Wadati-Benioff zones are in relation to sea-floor spreading
RTN 9.2 Q5) Why are the oldest parts of the ocean floor less than 200 million years old?
Oldest parts would have been in the process of subduction. Would have gone back to the mantle to become new rocks
RTN 9.2 Q6) How do magnetized rock on the ocean floor provide evidence of sea-floor spreading?
Strips of rock show what polarity they have. Since polarity on Earth alternates, means new rock formed during the period will have the same polarity. Shows proof that sea was enlarging
RTN 9.2 Q7) Would earthquakes occur at a depth of over 700km? Why or Why not?
No, because the subducting slab of ocean floor has been heated enough to soften. No earthquakes have been recorded below 700km
So what drives the Plate Movement?
Convection currents in the mantle provide the forces that drive plate's motion
(9.3) Plate Tectonics
Earth divided into 14 different tectonic plates
-Plates are made up of the lithosphere and move in the asthenosphere
-When 2 plates meet we call it a boundary
-There are 3 main types of plate boundaries
Three Types of Plate Boundaries
1) Divergent
2) Transform
3) Convergent
Divergent
-Two plates are moving apart ? ?
>When it happens in oceans, called sea-floor spreading (EX: Mid-Atlantic Ridge, East Pacific Rise)
>When occurs on continent, called rifting (EX: East African Rift-Zone, Iceland)
Transform
-Two plates slide past on another
-Causes large and frequent earthquakes
-NO volcanoes (California, San Andreas Fault)
Convergent
-Two plates are moving together and collide ? ?
-There are 3 different types of convergent boundaries
Continental - Continental Convergence
2 continental plates collide causing folded mountains and earthquakes (EX: Himalayas, Appalachias)
Oceanic - Oceanic Convergence
-2 plates collide
-One plate sinks craeting a subduction zone and Island Arc (EX: Japan+Indonesia+Aleutian Islands, AK)
Oceanic-Continental Convergence
-Oceanic crust collides with continental crust
-Oceanic crust is denser than continental crust, so it sinks, creating a subduction zone + volcanic mountains (Volcanic Arc)
(EX: Andes Mtns, Cascade mts{Mt. St. Helens, Mt. Rainier}
Hot Spots
-Occur in the middle of a plate
-Thought to be caused by a "hot spot" in the mantle
-Volcanic activity in the middle of a plate indicates a hot spot (EX: Hawaii, Yellowstone? Continental hot spot)
How do we know where boundaries are?
-Most earthquakes and volcanoes occur along plate boundaries
-Most volcanoes in world surround Pacific Plate
-This is called the Pacific Ring of Fire
Causes Plate Motion
-Convection in the mantle of the Earth
>Slab-pull: When cold ocean lithosphere (crust) descends into the mantle (EX: Subductionzones, Oceanic-Continental, Oceanic-Oceanic
>Ridge-push: When oceanic crust slides away from mid-ocean ridges (sea-floor spreadi