Units 26-27 Flashcards
What are the five categories of evidence that teach us about earth’s interior?
- Direct observation of rocks from interior
- Relationships to rocks or meteorites from space
- Inferences from Earth’s density
- Evidence from seismic (earthquake) waves
- Requirements for producing Earth’s magnetic field
What brings deep rocks to the surface that can’t be reached by drilling or other ways?
Volcano blasts and ascending magmas.
Crust
The uppermost compositional layer of Earth.
Characteristics of the crust:
Very thin
Composed of two parts: Granitic continental crust and basaltic oceanic crust
True or False: Rocks brought to the surface by volcanoes are denser than the basalts on the ocean floor.
True
Mantle
The middle compositional layer of earth.
Characteristics of Mantle:
Thick layer
Made of peridotite in the upper part
and higher density rocks of peridotite composition in the lower part.
Peridotite
Rock made up of mostly silicon, oxygen, iron, and magnesium.
True or False: Peridotite is denser than the basalt and granite of the earth’s crust
True
Meteorites
A rock from space that HITS earth’s surface
Stony chondrites
Meteorites thought to be composed of unprocessed material from the original solar nebula
The same materials that our planet and solar system were originally made.
What percentage of meteorites are stony chondrites?
86%
Stony achondrites
Meteorites thought to represent material from small planetary bodies that had differentiated into layers and then were broken up.
What percentage of meteorites are stony achondrites?
8%
Iron meteorites
Meteorites thought to represent the type of material found in Earth’s core
What percentage of meteorites are iron?
6%
Core
The deepest or central compositional layer of Earth. It is composed mostly of iron
What is the equation for Earth’s mass?
M = gR^2 / G
M = mass of earth
g = acceleration of gravity
R = radius of earth
Why do we care what Earth’s density is?
Because that tells us about the rocks that compose it.
Why do we care about Earth’s mass?
Because having the mass lets us calculate density
True or False: Earth’s surface is elastic
True
It rebounds back into shape when pressure is released
Elastic rebound
The point at which stress in Earth’s lithosphere is strained to a point where it can bend no further. When this happens, the lithosphere ruptures and rebounds somewhat like a rubber band that has just been pulled apart.
Fault
A break in earth’s lithosphere where rocks on one side of the break have slipped past the rocks on the other side
What causes faults exclusively?
Earthquakes
What characteristic of earth are faults a result of (not earthquakes)?
Elastic rebound
Tectonic plates
The brittle, rigid but thin outer part of Earth is divided into sections called tectonic plates
Seismic waves
Waves produced by earthquakes (caused by tectonic plates rubbing against each other, smashing into each other, and slipping.
Seismos translation?
Earthquake in Greek
True or False: Earthquakes simultaneously produce compression, shear, and surface waves.
True
Which type of waves travel fastest, compression, shear, or surface?
Compression
P waves
Primary waves.
These are compression waves produced by an earthquake. They travel the fastest so they reach the measuring detectors first (primary).
S waves
Secondary waves.
Shear waves. They are second to arrive at seismic detectors
What is the slowest type of wave?
Surface
Focus
Point of origin in an earthquake.
The place inside the earth where an earthquake originates
Epicenter
The point on Earth’s SURFACE directly above the focus of an earthquake
True or False: The speeds of P and S waves change depending on the type of rocks/materials they are passing through.
True
True or False: The stiffer the rocks, the slower the wave speed.
FALSE
The faster the wave speed
Why do wave speeds and directions REFRACT inside the earth’s surface?
Because of the properties and elasticity of the rocks they are travelling through, which vary by density.
Seismographs
The detectors in the grid of earthquake recording stations.
Seismometers
Device that measures ground motion
Seismic discontinuity
A place where the velocities of seismic waves change abruptly.
Moho
Short for Mohorovicic discontinuity. It is the location of the boundary between densities. At the base of the earth’s crust.
Shadow zone
A region of earth where seismic waves cannot be detected by seismometers.
Look at 26.7 figure. Easy.
Outer core
The upper part of the core that is made of liquid iron
How did we figure out that the outer core (or any part of the earth’s interior) was liquid?
Because of the shadow zones. Shear waves can only travel through a solid.
Inner core
The lower part of the core that is made of solid iron
What happens to the density as you move in through the core of the earth?
It increases
Curie temperature
The temp at which a material loses its magnetism (not a permanent magnet anymore)
True or False: Earth’s magnetic field is produced by a giant, iron core that is magnetized.
FALSE
The core is not magnetized (too hot, curie temperature explanation)
What causes earth’s magnetic fields?
Electrical currents in the earth
What causes the electrical currents in the earth?
The difference in temperature between the inner and outer core (solid and liquid) creates convection that move iron atoms in great cylindrical cells that rotate equatorially (earth’s rotation).
Relies on the Sun’s magnetic field.
True or False: There are many types of rock in the earth’s crust, including igneous, sedimentary, and metamorphic.
True
It averages granite
Silicates
Minerals that contain silicon and oxygen bonded together
True or False: The oceanic crust is virtually all basalt
True
Which is more dense, the oceanic or continental crust?
Oceanic
Dense oxides
Minerals that form deep in earth’s mantle due to the enormous pressures
What is another way to describe “mechanical layers”?
The physical behaviors of the rocks in the compositional layers of the crust, mantle, and core
What does mechanical behavior refer to?
How rocks deform when forces are applied to them.
Plastic
Non-rigid, deformable, capable of flowing in response to force or pressure.
Basically silly putty
Lithosphere
Earth’s outermost rigid, brittle, skin-like layer. Solid rock.
It consists of the crust and the outermost part of the mantle that is too cool to be molten.
True or False: The lithosphere is the only layer in which earthquakes can occur
True
Which mechanical layer is the Moho found in?
Lithosphere
True or False: Tectonic plates float
True
Asthenosphere
A soft, plastic, partially molten mechanical layer right below the lithosphere.
This is the layer that tectonic plates float on.
low velocity zone
A region of the upper mantle (asthenosphere) where seismic waves travel slower than expected.
What is the low velocity zone made of?
It is the boundary between solid peridotite and partially molten peridotite.
Melting point line
A line on a plot of temperature AND pressure showing where a substance transforms from a solid to liquid.
True or False: Melting points are influenced by temp AND pressure
True
Why does peridotite only partially melt?
Because it is made of many minerals with various melting temps
Mesosphere
The mechanical layer between the asthenosphere and the outer core
Is the mesosphere solid or liquid?
SOLID, but plastic, and able to flow.
It’s not the molten lava that everybody says it is.
How fast do the plastics in the mesosphere flow?
a few centimeters per year.
What causes flow in the mantle?
Pressure and temperature changes, density differences
True or False: The inner core is continually growing because iron is solidifying onto it.
True
They think
What keeps the center of the earth warm?
The enormous amount of heat released from the growing inner core
What is the AVERAGE density of earth?
5.5 g/cm^3
Why can P and S waves help us figure out where earthquakes start?
Because they travel at different speeds and reach different seismometers at different times.
What does a seismometer produce?
Seismographs
True or False: We have machines that can get us past the Earth’s crust.
FALSE
What is easier to understand if we assume that the earth is split up into abrupt layers?
Shadow zones (changes of density that create wave speed changes)
True or False: P waves are refracted as they encounter an abrupt change of medium
True
True or False: P waves that travel through the solid core reach the other side of the earth faster than those that did not.
True
Solids = faster waves
What is a “mechanical layer”?
The composition of the layers are the same, but the behaviors of the layers change due to temperature and pressure differences.
Why do we assume the core is made of iron and nickel?
Because meteorites are found that way, and if we ASSUME it’s iron and use that information in our calculations, Earth’s overall density seems to be correct.
Pangaea
The name of the supercontinent that broke up about 200 million years ago.
Who came up with “pangaea”?
Alfred Wegener
What does Pangaea mean in Greek?
“all earth”
Continental shelves
The ACTUAL edges of continents (underwater)
When did the theory of tectonics and pangaea become widely accepted?
1970’s
dang
Shield
The oldest parts of the continents. They represent the roots of very ancient mountains, long since eroded away.
Stable platform (covered shield)
An area of the continent where the old rocks of the shield have been covered by relatively flat-lying sedimentary rocks.
What is another name for a stable platform?
Covered shield
Mountain belt
Regions of the continents where rocks have been highly deformed by enormous forces. Usually along the edges of continents.
Structural trends
The orientations of major geologic features such as mountain belts, continental shields, stable platforms, and areas of folded or deformed rocks
Paleontologists
They study ancient life preserved as fossils in rocks
Glossopteris FLora
An extinct group of plants that lived 250 million years ago.
These fossils were found all over the world. Seeds could not have been spread across thousands of kilometers of open ocean through natural processes. Contributed to the idea of Pangaea
Mesosaurus
Water reptile 300 - 250 million years ago.
Again, found across oceans in fresh water, could not have happened (crossed the ocean) if ancient days were separated by oceans.
What evidence do glaciers present for Pangaea?
There are glacial remains in areas that are warm, and not in areas that are not cold. This helps us understand that tectonic plates moved those regions out of hot and into cold (vice versa).
Paleoclimatology
The study of ancient climates
What evidence did the mid Atlantic ridge provide when it was discovered in the 1950’s-60’s?
It aligned almost perfectly with the shelf margins on either side of it, showing that the seafloor MOVED, and was the mechanism that moved the continents.
Where are the oldest ocean rocks found, closer or farther away from the continents in their present positions?
Farther away
True or False: The youngest rocks on the ocean floor are found next to the mid-ocean ridges
True
Seafloor spreading
Theory that the ocean floor GROWS on either side as the mid ocean ridge moves apart.
The rift created in this process is filled in with BASALT as magma squeezes up into the fractures created by rifting.
What causes the continents to move?
Seafloor spreading, pushing them apart
True or False: Earth reverses its polarity (magnetic field) every half million years
True
Where are earthquakes happening (not lithosphere, surface features)
Along the ocean trenches and ridges
What is happening to the lithosphere at ridges?
The brittle lithosphere is being pulled apart
What is happening to the lithosphere at the trenches?
It’s sinking back into the asthenosphere
Ridge push
Helps move earth’s plates. The ridge is high and has gravitational potential energy that is converted into kinetic energy as the plate moves.
This is how tectonics “flow” like liquids.
What forces move tectonic plates?
Ridge push
Slab pull
Slab pull
As an oceanic plate becomes old, cold, and dense, it sinks back into the mantle, pulling the rest of the plate along with it (helped by ridge push which is pushing up the other end).
Divergent plate boundaries
Boundaries where two plates are splitting apart from each other
Convergent plate boundaries
Boundaries where two plates are colliding with each other
Transform boundaries
Boundaries where two plates are sliding past each other.
True or False: Earthquakes on oceanic ridges produce tsunamis
False
They’re milder than collisions
True or False: Continental lithosphere is colder than oceanic lithosphere
True
Because it’s older
Why does some lithosphere have to be destroyed?
Because earth isn’t growing in size, and lithosphere is being created elsewhere. To “make room” it has to lose some.
What is common at convergent plate boundaries?
Spectacular mountains, huge earthquakes, and explosive volcanoes
What are the three subtypes of convergent boundaries?
- ocean ocean
- ocean continent
- continent continent
Subduction
Occurs with collisions between two ocean plates.
In a collision of two ocean plates, one will dive under the other and sink into the asthenosphere.
Which plate sinks in subduction?
older and colder (therefore DENSER)
True or False: Subductions create massive earthquakes and tsunamis
True
Volcanic island arch
A chain of volcanoes, shaped like an arc, that form at some convergent plate boundaries
True or False: When an oceanic plate collides with a continental plate, it is always the oceanic plate that subducts.
True
What is often created by ocean-continent collisions?
Volcanoes and mountain belts
True or False: Continents that collide into each other crash like two cars in a head-on collision. Neither sink.
True
What happens to separate continents that crash into each other?
They become welded together, creating the highest mountain ranges on earth
What is one striking difference between continent to continent collisions vs. other collision types?
No volcanoes (because nothing is sinking into the mantle)
Mantle plume
A buoyant mass of hot rock rising through Earth’s mantle. As it nears the surface of Earth, some of the plume melts and erupts at the surface forming a hot spot.
Hot spot
Many volcanoes that result from the lithosphere moving over a mantle plume.
Hawaii is example.
Hot spot trail
The trail of volcanoes as the lithosphere passes over the hot spot.
Linear island chains
A chain of volcanic islands created when an ocean plate moves over a hot spot.
Why do hot spot volcanoes become extinct?
Because the land mass has moved past the mantle plume so it’s no longer being fed by magma.
True or False: The same forces that tore Pangaea apart are the same forces that originally assembled it.
True
Continental accretion
The process by which continents grow. When continents collide with other land masses, new material may be added and the continent grows.
Summarize paleomagnetic evidence of Pangaea
Magma has magnetite that flows in the direction of the magnetic field. When the magma cools, it freezes in place. We can look at the directions that the magnetite was flowing to see where it came from, and where those land masses fit with OTHER magnetite flows.
How quickly do oceanic plates diverge?
3-10 cm / year
True or False: At a continental divergence, an ocean can form if the rift continues
True
True or False: All continental divergences cause rifts that continue indefinitely
False.
They can stop
