Science 7: Earth's Crust
Restless Continents, Plate Tectonics, Deformation of the Earth's Crust
Terms in this set (55)
The Continental Drift theory
All of the continents were once one large landmass that has broken up and drifted apart
The scientist who hypothesize the continental drift theory
4 Pieces of Evidence of Continental Drift
- continents fit together like pieces of a puzzle
- fossils of the same species of animals and plants found on separate continents, ex. Glossopteris
- rock formations, ex. matching mountains chains
- climate conditions, ex. coal fields in Antarctica
Greek for "all Earth."
List the two huge continents Pangaea broke into:
Laurasia (north) & Gondwana (south)
underwater mountain chain that runs through the Earth's oceans
What occurs at mid-ocean ridges?
the process in which new lithosphere forms
Process of sea-floor spreading
-Magma rises to the surface through the mid-ocean ridge, forming new oceanic crust;
-Tectonic plates spread apart and magma fills the gap;
-As new crust forms, older crust moves away from the mid-ocean ridges
List two pieces of evidence that sea-floor spreading has occurred
- Crust closer to the mid-ocean ridges is younger than crust further away.
- Magnetic reversals recorded in the ocean floor
the process in which old ocean floor goes back into the mantle through trenches
- Earth's north and south poles have changed places many times
- Molten rock contains tiny grains of magnetic minerals
- These minerals align with the magnetic field of the Earth
Theory of plate tectonic
The Earth's lithosphere is divided into tectonic plates that move around on top of the asthenosphere.
Where did the theory come from?
Combination of continental drift and ocean floor spreading theories
What are tectonic boundaries?
Places where tectonic plates touch
Three types of plate boundaries
boundary formed when tectonic plates collide
boundary formed when tectonic plates separate
boundary formed when tectonic plates slide past horizontally
Three ways that tectonic plates can move relative to each other
Collide, separate, slide
When/where two tectonic plates collide
Three types of collision
- Oceanic- Oceanic
- Oceanic - Continental
- Continental - Continental
Oceanic-Oceanic collision (or convergence)
- More dense plate subducts (dense - heavier)
(a more dense plate sinks below a less dense plate)
- Sometimes creates an island arc
- Oceanic plate subducts (sinks under continental plate)
(Oceanic plate has a higher density)
- Creates a volcanic arc
Plates fold upward to form mountains
When two plates with continental crust collide, what happens to continental crust?
The continental crust buckles and thickens, which pushes the continental crust upward.
When two tectonic plates separate
What is most common type of divergent boundary?
What occurs at divergent boundaries?
New land is formed along a divergent boundary.
(New sea floor forms at divergent boundaries. p. 109)
When two tectonic plates slide horizontally past each other
What happens at transform boundaries?
Transform boundary is where most earthquakes occur.
What is an example of a transform boundary?
San Andreas Fault
Causes of plate motion
- Convection currents
- Rodge push
- Slab pull
When rock is heated, ________
it becomes less dense and tends to rise
When rock cools, ______
it becomes more dense and tends to sink below the surface.
Density changes in the asthenosphere are caused by the flow of ______
thermal energy/heat from deep within the Earth
Plate motion due to higher densities
Plate motion due to gravity
Plate motion due to the heating and cooling of rocks
What are convection currents?
Caused by differences in density of materials due to heat
- hot less dense material rises
- cooler more dense material sinks
- causes circular currents in the mantle
- causes the oceanic lithosphere to move sideways and away from the mid-ocean ridge
How does GPS help scientists study plate motion?
Scientist use GPS to track the rate of motion of tectonic plates.
Satellites send signals to the ground stations, and over time, these distance will change, showing a change in plate position.
What is deformation?
The process by which the shape of a rock changes because of stress.
Give 2 examples of stress causing deformation
Compression - object is squeezed
Tension - object is stretched
what is a folding?
The bending of rock layers because of stress in the Earth's crust
List the type of folding
Anticlines - upward-arching folds
Synclines - downward, troughlike folds
Monocline - both end of fold are horizontal
What is a fault?
The surface along which rocks break and slide past each other
What is normal fault?
It causes the hanging wall to move down relative to the foot wall - tension
What is reverse fault?
It causes the hanging wall to move up relative to the foot wall - compression
What is strike-slip fault?
It forms when opposing forces cause rock to break and move horizontally
Name three types of mountains that are fored
Folded mountains Fault-Block Mountains, Volcanic Mountains
What is uplift?
The rising of regions of Earth's crust to higher elevations
What is rebound?
When the crust slowly springs back to its previous elevation
What is subsidence?
The sinking of regions of Earth's crust to lower elevations
What is the rift zone?
A set of deep cracks that forms between two tectonic plates that are pulling away from each other
What is tectonic letdown?
As tectonic plates pull apart, stress between the plates causes a series of faults to form along the rift zone.