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What is the Theory of Continental Drift?

The belief that Earth's continents were once joined as a single landmass and have slowly moved to their current positions and continue to move today.

What is Pangaea?

The name of the supercontinent Alfred Wegener believed existed over 200 MYA

How did evidence from rock formations support Wegner's theory?

Rocks of the same age, from the same processes and type are found in bands where continents were once connected. Mountain ranges line up in Africa and South America, as well as in North America, Greenland, and Europe.

How did evidence from fossils support Wegner's theory?

Fossils of Cynognathus, a land dwelling dinosaur is found on multiple continents. Mesosaurus, a freshwater dinosaur, is found across multiple continents. These fossils could only be in these locations if they continents were once joined.

How did climatic evidence support Wegner's theory?

Coal beds were found in Antarctica and tropical plant fossils are found near the Arctic Circle. This could only happen if these areas were much closer to the equator in the past.

Why was Wegner's theory rejected?

He could not explain the forces responsible for moving continents.

What are mid-ocean ridges?

A continuous mountain chain that forms at divergent boundaries in the ocean floor.

What are deep-ocean trenches?

Elongated, deep, narrow depressions that form in subduction zones.

Where are the youngest rocks on the seafloor found? Why?

They are located at the mid-ocean ridges because new crust forms there as magma rises to the Earth's surface.

Where are the oldest rocks on the seafloor found? Why?

They are located at deep ocean trenches because rocks get pushed away from the mid-ocean ridges during the process of seafloor spreading and they subduct back into the mantle.

What is a magnetic reversal?

When Earth's magnetic field "flips" and magnetic north is located at the south pole and vice versa.

Explain the magnetic symmetry of the ocean floor.

Magnetically aligned iron bearing minerals "lock" into stripes as they cool. The stripes are symmetrical and this shows that the seafloor is spreading evenly from the mid ocean ridge towards the continents.

What is an isochron?

A line on a map that connects areas of equal age

Explain the process of seafloor spreading.

New oceanic crust is created at mid-ocean ridges as less dense magma rises at this divergent boundary. The newly formed rocks push older rocks along the ocean floor towards the continents were they subduct into trenches when they collide with less dense continental crust.

What are tectonic plates?

Large slabs of crust that move in relation to each other.

How fast do tectonic plates move?

2 - 5 cm per year

Identify the three types of plate boundaries.

Convergent, divergent, and transform

What is a divergent boundary and where do most occur?

A boundary where plates pull apart under tension stress. Most of these occur on the ocean floor.

What are convergent boundaries?

A boundary where plates collide under compression stress.

What is subduction?

The process of a less dense plate sinking beneath a denser plate.

What is a transform boundary?

Boundary at which two tectonic plates move in opposite directions horizontally (shearing stress)

By what are transform boundaries characterized?

Lack of vertical movement

What is convection?

The process of a warmer, less dense fluid rising, cooling, becoming more dense and sinking back down. Heat is transferred to surrounding molecules as the fluid circulates.

What is the driving mechanism of plate tectonics?

Convection currents in the mantle

How is movement at divergent and convergent boundaries related to mantle convection?

When the mantle bumps into the tectonic plates, it will cause ridge push, basal drag, and/or slab pull as the material moves along the bottom of the crust, pulling plates apart or pushing them together.

What is volcanism?

Any processes by which magma rises through the crust towards Earth's surface.

Where do most volcanoes occur?

Pacific Ring of Fire

Describe the Ring of Fire

The subduction zone around the edge of the Pacific plate where most earthquakes and volcanoes occur.

What is a hot spot and give an example?

A weak spot in the Earth's crust through which magma erupts onto the surface. Often found far from plate boundaries

Explain the ages of the islands of Hawaii.

Hawaii is the youngest island, then they progressively get older as the chain moves to the NW due to the Pacific plate moving away from the hot spot that formed the islands.

What is a vent?

An opening in the top of a volcano through which magma erupts onto the surface.

What is a crater?

A bowl shaped depression that forms around volcanic vents.

What is a caldera and how can it become a lake?

A large crater that forms as a result of a volcano either collapsing upon itself or exploding when a magma chamber empties during an explosive eruption. It can become a lake if it becomes covered by glacial ice that melts as the glacier retreats during warm periods.

Identify the three types of volcanoes.

Shield, composite, and cinder cone

What is a shield volcano and give an example.

A shield volcano forms as a result of repeated quiet eruptions produce thin, runny lava flows that build up over time. They are the widest but least steep volcanoes. Kiluaea is an example.

What is a cinder cone and give an example.

A volcano that forms as a result of explosive eruptions which accumulate steep, but not very tall mountains of volcanic ash, cinders, bombs, and other tephra. Paricutin is an example

What is a composite volcano and give an example.

A volcano that forms from alternating quiet and explosive eruptions that forms a tall, majestic mountain formed from lava flows and tephra accumulation. Mt. St. Helens is an example.

What happens to temperature and pressure with depth beneath the surface?

Both INCREASE with depth

What determines a volcano's ability to explode?

The gas content of the magma

Describe how the amount of dissolved gases in magma affect its ability to explode.

The higher the gas content, the more pressure builds in the magma. Eventually this pressure is released in an explosive eruption.

What is viscosity?

A substance's ability to resist flow.

Describe how the silica content of magma affects its properties.

Magma that is high in silica will have a high viscosity and appear lighter in color. The high viscosity will trap gases and cause more explosive eruptions. Magma that is low in silica has the opposite properties.

Describe a quiet eruption.

An eruption of low viscosity magma that releases gases readily, therefore flowing lava out of the vent rather than exploding out of the mountain.

What causes an explosive eruption?

Pressure build up inside the volcano

What is a pyroclastic flow?

Rapidly moving clouds of tephra and hot gases with speeds in excess of 80 km/h

What is a pluton?

Intrusive igneous rock bodies

What is a batholith?

A large (100km2) irregularly shaped pluton formed from coarse-grained igneous rock

What is a stock?

A smaller batholith

What is a laccolith?

A lens shaped pluton with a round top and flat bottom

What is a sill?

A horizontal igneous intrusion that runs parallel to rock layers

What is a dike?

A vertical igneous intrusion that cuts through rock layers

What is the cause of most earthquakes?

The movement of Earth's crust due to plate tectonics

What is stress?

Any force that acts upon a rock

Identify the three types of stress.

Tension, compression, shearing

What is a fault?

A break in the Earth's crust along which the Earth moves

Identify the three kinds of faults.

Normal, reverse, strike-slip

What is a reverse fault?

A fault in which one block of rock above the fault line is thrust upwards due to compression stress

What is a normal fault?

A fault in which one block of rock above the fault line sinks down due to tension stress.

What is a strike-slip fault?

A fault in which there is no vertical movement - the blocks of rock move alongside each other under shearing stress.

What type of stress causes each type of fault?

Reverse - compressional

Normal - tensional

Strike Slip - shearing

What are seismic waves?

Energy released during an earthquake that travels in all directions

Identify the three types of seismic waves.

Primary, secondary, and surface waves

Describe primary waves.

Fastest body waves that move through compression and expansion through and on the Earth

Describe secondary waves

Second fastest body waves that cause rocks to move perpendicular to wave motion (known as shear waves)

Describe surface waves.

Slowest most damaging waves. Two types: Love and Rayleigh. They only travel along Earth's surface and roll like ocean waves or shear the rock.

Through what types of materials can P waves and S waves travel?

P waves can travel through any substance while S waves cannot travel through liquids

What is the focus of an earthquake?

The point below the Earth's surface where the rock has failed (broke or slipped)

What is the epicenter of an earthquake?

The point on the Earth's surface above the focus.

What is a seismometer?

A tool that records seismic waves

In what order do seismic waves reach a seismograph?

P waves first, then S, then surface. Depending on the location of a seismometer - not all waves may be recorded

How does the difference in arrival time between P and S waves determine epicenter distance?

The greater the lag time (S and P interval) the further from the epicenter the seismic station is located.

What is the S-wave shadow zone?

The S wave shadow zone is the region in which no s waves would be recorded because the outer core (liquid) is between the focus and the recording station

How do seismic waves provide geologists Information about the Earth's interior?

Scientists can determine the thickness and composition of each layer by studying how P and S waves move, the path, and change speed and direction as they travel through the Earth.

What is the Richter Scale?

A scale used to rate earthquakes based on the strength of the largest seismic waves

What is magnitude?

A measurement of the energy of a seismic wave

What is the Moment magnitude Scale?

A rating scale used to measure earthquakes based on the energy released by the quake that considers the size of the fault, the movement along the fault, and the stiffness of the rock.

What is the Mercalli Scale?

A scale that rates earthquakes based on the damage the cause (intensity) and the effects of the quake AFTER it has occurred.

How is the epicenter of an Earthquake located?

Triangulating data from at least three monitoring stations using the S - P arrival interval.

What is soil liquefaction?

The ground behaves like a liquid when an earthquake hits an area with soil that is saturated

What is a tsunami?

A large wave that results from an earthquake in the ocean

What is topography?

Variations in elevations of Earth's crust

What percentage of the Earth's surface is above sea level? Below sea level?

71 percent is below sea level, 29 percent is above.

Of what is oceanic rock composed and what is its density?

Basalt; 2.9 g/cm3

Of what is continental crust and what is its density?

Granite; 2.8 g/cm3

What is the density of the mantle?

3.3 g/cm3

What is isostasy?

The balance between the downward force of gravity on earth's crust and the buoyancy of the mantle

What are roots?

Large masses of rock subsided into the crust to counterbalance the weight of the mountains

What happens to mountains' roots when crust is eroded?

The roots rise in response to the reduced weight, eventually becoming exposed

What is isostatic rebound?

The rising of the crust in response to the removal of material.

What is orogeny?

Processes that form mountains

What are compressive forces?

Forces that squeeze crust and cause deformation

How are the three kinds of convergent boundaries classified?

By the types of crust involved

What happens at oceanic-oceanic boundaries? Give an example.

The denser plate subducts and the less dense plate forms a small volcanic mountain. Aleutians are an example

What happens at oceanic- continental boundaries? Give an example

The oceanic plate subducts and a volcanic mountain range forms as a result. The Andes are an example.

What happens at continental- continental boundaries? Give an example.

Neither plate subducts and high mountain ranges form. The Himalayas are an example

Rank the mountains formed at each convergent boundary according to size (tallest to smallest).

C-C are the tallest, O-C are next, and O-O are smallest

Describe the mountains formed at divergent boundaries.

Mountains that form at divergent boundaries form due to uplift of heated, less dense rock at the boundary.

Describe an uplifted mountain?

Large sections of rock rise slowly upward as a unit