What role does gravity play in the layering of planets?
Solid Iron (the heaviest) makes up the core. The outer core is made of liquid iron. The Lower mantle is a solid rocky mantle. Upper mantle is lighter and rocky. Gravity causes respective layering.
What are the 2 major reasons for the increase in density with depth within Earth's mantle?
1) Compression resulting from increased pressure 2) Mineral phase change
Why is seismology responsible for gas prices being more affordable than they might be w/o seismology?
b/c without it a huge number of wells would have to be randomly drilled to find oil. seismology helps find structures where petroleum may be trapped
3 ways that oceanic crust and continental crust differ. Where is the thickest crust found? The thinnest crust?
1. Oceanic crust is created at mid-ocean ridges, continental varies 2. Oceanic crust has similar composition and thickness throughout while in continental it varies. 3. Oceanic crust averages 7 km thick while cont is 40-70
What is the importance of determining the cross-over distance?
It is important to find the thickness of crust for any location. refracted waves enter mantle, seismographs near the center record waves first then seis mos further from center record waves 2nd. pt at which both waves arrive at same time is cross-over
How do S waves tell us the mantle is solid?
B/c they go through it but then are blocked my liquid outer core
If there were a lot of water in Earths mantle, in what layer would it most likely reside?
The transition zone within the upper mantle
What mineral phase changes occur at the top and bottom of the transition zone?
Olivine. in the top it converts to B-spinel and in the bottom it converts to more compact ringwoodite
What layer of Earth has the greatest volume?
The Lower Mantle. perovskite is the single most abundant material within the earth
How is the D layer similar to the lithosphere?
-both have large variations in composition and temperature
T or F: No seismic waves arrive in the shadow zones. Explain
F. Some do. All S do not because they dont travel through liquid but most P waves get refracted similar to how light passes from air to water
Why is Earth's core 1/6 of Earths volume but 1/3 of its mass?
b/c it is composed mostly of iron which is the most dense of the common elements.
Describe how earths inner core grows in its size.
As Earth cools, iron began to crystallize and core grows. Liquid outer core allows it some space.
Why is heat flow from Earths surface not evenly distributed?
earth loses most of its heat near mid ocean ridges where magma rises toward the surface to fill the cracks where tectonic plates pull apart. Continents lose heat fastr than old oceanic seafloor bc they contain higher amts of heat producing isotopes
Describe the heat sources that caused Earth to get very hot early in its history.
1st stage involved rapid increase in internal temp. earth formed through collisions of baby planets.more collisions=more kinetic energy. as earth grew, temp increased, contained many short lived radioactive isotopes (released radiogenic heat)
What prevents Earth from being a cold, motionless sphere of totally solid rock and metal?
convection with mantle, sinks cold oceanic lithosphere back into deep mantle
Conduction and Convection
Conduction-the transfer of heat through matter by molecular activity Convection-transfer of heat by mass movement or circulation of a substance
Why is Convection an inefficient means of heat transfer in materials with high viscosity?
b/c these materials resist flow/are too strong to flow and thus do not move the heat in a fluid-like manner
Why is conduction more important than convection within Earth's crust?
b/c the iron-rich material in core is too dense to intrude (convect) into less thermal rocks. for the thermal energy to leave the core, it must conduct across the core-mantle boundary and up through the D layer. after upper mantle, conducts in litho
What happens to rock as the geotherm approaches its melting temp?
it begins to soften and weaken
What happens to rock in regions where the geotherm crosses above the melting point curve?
material becomes molten
Why would tectonic plates have a hard time moving if it were not for the existence of the asthenosphere?
bc the asthenosphere is weaker and softer bc it is close to melting temp
Why is the lithosphere stiffer than the asthenosphere?
bc its temp is much colder than its melting temp.
Earth once rotated much faster than it currently does. How would Earths shape have been different in the past?
it would have been more rounded than ellipsoid (poked out on sides)
Would you expect to find a large layer of iron ore underground in a region w/ a positive or neg. gravity anomaly? Explain.
Positive because this is where thick, dense volcanic rocks filled a rupture in the crust more than a billion years ago.
Why does the mid-Atlantic ridge appear as a slow seismic velocity anomaly in fig 12.20
b/c it is hotter and more tectonically alive making this portion weaker and warmer which slows S waves
What are the 3 driving forces of convection in the outer core?
1.heat conducts out of core into mantle, outermost core cools,becomes denser and sinks 2.crystallization of solid iron sinks to form inner core,leaves behind fluids, drives chem. convection 3.radioactive isotopes in core that drive thermal convection
What occurs during a magnetic reversal?
Earths magnetic field reverses polarity so the north needle on a compass would point south. during:the strength of the magnetic field decreases to about 10% and poles locations begin to wander.
Why might a magnetic reversal be dangerous to humans?
could cause health hazards w/ excess ionized materials
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