Tectonic plates

Question 1

GPS (evidence for plate tectonics theory)

Answer 1

GPS satellites are used to determine precise locations of instruments through triangulation
.By measuring one location continuously, the distance moved over the time of measurement can be determined.
Gps can measure the movement of tectonic plates, and their velocity

Question 2

Hot spots/mantle plumes

Answer 2

Hotspots and mantle plumes are the same, a place in the Earth which is disproportionately hot, rock heats and rises up, melts due to decompression
Hot rock undergoes decompression melting, forming magma that can feed volcanic activity
Hot spots record plate motion by leaving a chain of volcanoes along its direction of movement

Question 3

mid ocean ridges and magnetism

Answer 3

Earth’s magnetic field is generated by movement of molten iron in the outer core. It is extremely important as it protects us from solar winds.
Magnetic orientation of earth is changing! And it has done so spontaneously throughout earth’s history.
Normal polarity is when the north pole was where it is today
Reverse polarity is when the north pole was at the present day south pole
Magnetic materials in most rocks align with earth’s magnetic field as they cool, becoming tiny magnets
These rocks can tell us what the earth’s magnetic field was like at the time of formation
At mid ocean ridges, we see patterns of polarity as rocks form over time, strips of normal, reverse, normal, symmetrical on both sides

Question 4

Transform boundaries

Answer 4

Plates sliding along one another
Also known as a transform fault, these zones occur when plates slide past one another; No new lithosphere is created.
Not normally associated with volcanism, but highly associated with earthquakes

Question 5

rock age at mid ocean ridges

Answer 5

Crust is youngest at the plate boundary, and is older the further away from the plate boundary you are.
Older crust is denser than younger crust

Question 6

mid ocean ridges

Answer 6

Occur at divergent oceanic-oceanic boundaries
Mantle upwelling occurs as plates pull apart.
Decompression melting occurs as the hot material is subject to less pressure.
New rock formation occurs at mid-ocean ridges.
Process is known as seafloor spreading
Seafloor spreading is why oceanic rock is younger than continental rock. New igneous rock is being formed at mid ocean ridges.

Question 7

Rift Valley

Answer 7

Two continental plates pull apart from one another
Fractures (faults) form in both plates near the boundary
Slab between faults eventually ‘falls’, creating the rift.

Question 8

divergent boundaries general

Answer 8

Plates moving away from each other
Mostly occurs in oceans at mid ocean ridges
If it occurs with ocean-ocean crust, it will form a mid ocean ridge
If it occurs with continental-continental crust, it forms a rift.

Question 9

Convergent boundaries

Answer 9

Plates moving toward each other and colliding, leading one plate to subduct
Subduction
Denser plate subducts, either OCEANIC or OLDER
What happens depends on types of crust involved

Question 10

Subduction

Answer 10

Subduction is the ‘sinking’ of of one lithospheric plate below another at a convergent boundary. Which plate subducts depends on the crustal types at the boundary.

Question 11

velocity of pacific plate/plates on average

Answer 11

The Pacific Plate moves northwest at a speed of between 7-11 cm per year
Tectonic plates on average move 0.6 to 10 cm per year

Question 12

Inner core

Answer 12

Creates Earth’s magnetic field
Hottest part of the Earth, temp between 5000-6000 degrees Celsius
Roughly 1400km thick
Mostly iron and nickel
solid

Question 13

Outer core

Answer 13

Layer surrounding inner core, approximately 2400km thick
Mostly made of liquid iron and nickel

Question 14

Mantle

Answer 14

Mostly oxygen, silicon, magnesium
2900km thick (thickest layer of Earth)

Question 15

Lower Mantle

Answer 15

below lithosphere and asthenosphere
Just as hot as upper mantle, remains solid due to pressure, slowly moving due to convection currents
Convection currents - when deeper hotter material rises, then cools, then sinks again, though to move the Earth’s tectonic plates (happen here)

Question 16

Asthenosphere

Answer 16

Upper part of mantle but below the lithosphere (plastic, rock is softer and partially molten)

Question 17

All layers of the Earth, subclassifications as well

Answer 17

crust, lithosphere, asthenosphere, stiffer mantle, mantle, inner core, outer core, core

Question 18

Crust

Answer 18

mostly oxygen and silicon; notably less iron and magnesium than mantle
Oceanic crust (5-8km, mostly basalt)
Continental crust (8-70km, mostly granite)

Question 19

geological evidence

Answer 19

Mountains in Eastern North America & Northern Europe match up.
Rocks in South America and Africa match up

Question 20

paleoclimatic evidence for continental drift

Answer 20

Evidence of glaciation, solved by putting the continents together

Question 21

fossil evidence for continental drift

Answer 21

~ 180 Ma, Pangaea began to break up into separate continents.
Supporting evidence: remains from ancient animals and plants from South America, Africa, India, and Australia that were almost identical.
No mechanism to transport across ocean
Evolutionary divergence of species following break-up
Fossil examples (memorize 1)
Glossopteris : a plant found on the southern continents
Cynognathus : a land reptile found in South America and Africa
Lystrosaurus: a land reptile found in Africa, Antarctica, and India
Mesosaurus : a freshwater swimming reptile found in Africa and South America
distribution of fossils across continents only makes sense if the continents were once together.

Question 22

How tectonic plates move (convection currents)

Answer 22

Convection occurs when material is heated (from core), rises due to a reduction in density, cools, and sinks. The plastic nature of the asthenosphere allows this to occur.
Thought to be the primary driver of plate motion.

Question 23

Oceanic vs Continental crust (density, composition, thickness, rock type)

Answer 23

Continental plates are composite.
Include both continental and oceanic crust.
North American Plate
continental portions are thicker, lower density lithosphere, mostly granite, igneous rock, felsic
120 km thick in continental regions.
oceanic portions are thinner, denser, lower (sea level), mostly basalt, igneous rock, mafic

Question 24

continental-continental convergent boundary

Answer 24

Continental Crust has a low density and is much more difficult to subduct.
Result is often large mountain chains

Question 25

oceanic-continental convergent boundary

Answer 25

When oceanic and continental crust collide, denser oceanic crust subducts below less dense continental crust
Subducting plate releases water, causing magma generation in mantle
Volcanic arc formation