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100 Cards in this Set
- Front
- Back
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What caused Alfred Wegener to propose the continental drift theory?
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- the continents could be fitted together like puzzle pieces
- the fit including continental shelves was better |
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What is the continental drift theory?
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the theory that the continents have not always been in their present locations but have moved there over millions of years
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What evidence supports the continental drift theory?
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- evidence of different climates on continents that now have warm climates
- matching geological features and rocks on different continents - matching fossils found on different continents |
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What is Wegener's supercontinent?
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a giant landmass named Pangaea that joined all the continents
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What is paleoglaciation?
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the extent of ancient glaciers and the rock markings left behind
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Give two example of evidence that support paleoglaciation
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1. Scientists have discovered evidence of glaciers in areas that are now tropical
2. Coal deposits found in Antarctica (coal is made of decomposed remains of once-living things; usually tropical swamp material) |
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What did Wegener not explain that we understand today?
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- did not explain how the continents moved
- we know that Earth consists of tectonic plates - tectonic plates slide over a layer of partially molten rock - a map of volcanoes and earthquake zones aligns with the outline of tectonic plate boundaries |
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What are tectonic plates?
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large slabs of rock that form Earth's surface, moving over a layer of partly molten rock
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What are volcanoes?
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openings in Earth's surface that, when active, spews out gases, chunks of rock and melted rock
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What is an earthquake?
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a sudden, ground shaking release of built-up energy at or under Earth's surface
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What is the Mid-Atlantic Ridge?
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the longest mountain range on Earth, running north to south down the middle of the Atlantic Ocean
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What did the mapping of the ocean floor in 1872 reveal?
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- the Mid-Atlantic Ridge
- the youngest rocks were found closest to the Mid-Atlantic Ridge and older ones farther away - the layer of ocean sediment became thicker further away from the ridge |
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Why does a compass needle, iron and other magnetic metals in rocks point North?
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they align with Earth's magnetic field lines
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What is a magnetic reversal?
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the process in which Earth's magnetic field, over thousands of years, completely reverses its direction
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What causes magnetic reversals?
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changes in the motion of the liquid iron in Earth's interior
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What happens to Earth's geographic North Pole and South Pole during a magnetic reversal?
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Because magnetic reversals do not affect Earth's physical appearance, they do not change
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What is paleomagnetism?
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the study of the magnetic properties of ancient rocks
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In the 1950's what did the magnetometers detect?
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a pattern of stripes in the direction that iron containing materials pointed on the sea floor (magnetic striping)
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What is magnetic striping?
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a pattern of alternating strips of different directions of magnetic polarity in rock on the sea floor
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What evidence provided support for the explanation of sea floor spreading?
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data on the age of ocean rocks, sediment thickness and magnetic striping
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What is magma?
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molten rock beneath Earth's surface
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What is a spreading ridge?
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the region where magma breaks through Earth's surface, continually forcing apart old rock and forming new sea floor
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What is sea floor spreading?
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the process in which magma rises to Earth's surface at spreading ridges and, as it continues to rise, pushes older rock aside
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What is Hess's evidence for sea floor spreading?
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1. Earth is like a large bar magnet and has two poles
2. New ocean floor forms when magma from under Earth's surface rises, cools, and hardens at an ocean ridge. New magma pushes older rock away from the ridge 3. The magma is molten basalt, a dark rock that is rich in iron; as it cools it becomes magnetic 4. The magnetic minerals in the hardened basalt are like tiny compass needles that align with Earth's magnetic field 5. Earth's magnetic poles reverse over hundreds of thousands of years 6. Minerals in the basalt keep the alignment they had when the rock had cooled; some will have normal polarity while other will have reverse polarity 7. Rocks with magnetic striping, alternating bands of normal and reverse polarity surround ocean ridges 8. The pattern of magnetic striping is the same in rocks on either side of an ocean ridge 9. Ocean sediments are thicker the farther away they are from a ridge because the oldest rock is farthest away from the ridge and has had the most time to accumulate sediments |
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What did J. Tuzo Wilson unify?
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the ideas of sea floor spreading and paleomagnetism to explain continental drift known as the Plate Tectonic Theory
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How did the Hawaiian Islands form?
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When a tectonic plate passed over a stationary hot spot
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What is a hot spot?
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an area where molten rock rises to Earth's surface
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What does the Plate Tectonic Theory explain?
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- formation of mountain ranges and ocean basins
- causes of earthquake's and volcanic eruptions - movement of tectonic plates - transformation of rocks from one type to another in the rock cycle - formation of the Hawaiian Islands |
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How did Earth form?
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- began as a molten ball 4.5 million of years ago
- as it cooled, denser materials sank towards Earth's core, less dense materials floated to the top and formed the crust - 3/4 of crust is made of silicates - crust + uppermost mantle = lithosphere (65-100 km thick) - 12 major tectonic plates form the lithosphere |
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What are the two types of tectonic plates?
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continental (mostly granite) and oceanic (mostly basalt)
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What is the lithosphere?
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the layer of Earth made up of the crust and uppermost mantle and ranging in thickness from 65km to 100km
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What four distinct layers make up the Earth?
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crust, mantle, outer core and inner core
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What is the crust?
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outermost solid rock layer
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What is the mantle (upper and lower)?
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thickest layer, mostly solid except for upper mantle which is able to flow like "thick toothpaste"
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What is the outer core?
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layer below the mantle composed of liquid iron and nickel
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What is the inner core?
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lies at Earth's centre; mostly solid iron at tremendous temperature and pressure
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What is the asthenosphere?
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a partly molten layer in Earth's upper mantle just below the lithosphere
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What is the effect of radioactive elements on the asthenosphere?
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- provides heat to keep the asthenosphere molten
- causes temperature to vary as there is large amounts of elements in some areas |
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What forms in the asthenosphere?
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a convection current forms as hot, low density magma rises
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What is mantle convection?
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a recurring current in the mantle that occurs when hotter, less dense material rises, cools, and then sinks again; this current is believed to be one of the driving forces behind tectonic plate movement
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When does magma cool?
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when it reaches Earth's surface at spreading centres
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What do spreading centres in oceans result in?
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spreading/oceanic ridge
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What do spreading centres on land result in?
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rift valleys
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What is a ridge push?
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magma cools, solidifies, and is pushed aside as new magma pushes up from below
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What is a rift valley?
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a steep-sided valley formed on land when magma rises to Earth's surface at a spreading center
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What is subduction?
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the action of one tectonic plate pushing underneath another
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What are subduction zones?
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areas of subduction, which typically experience large earthquakes and volcanic eruptions
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What is a slab pull?
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the pulling of a tectonic plate as its edge subducts deep into the mantle
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Describe motion of tectonic plates
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they move at the same time
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What happens when oceanic and continental plates meet?
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- oceanic plate will go under the continental plate because it is denser
- oceanic plate subducts under continental plate - "slab pull" the rest of the plate will follow - creates an area of subduction and large earthquakes and volcanic eruptions occur |
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What occurs near subduction zones?
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large earthquakes and volcanic eruptions
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What is a plate boundary?
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the region where two tectonic plates are in contact
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What is plate interaction based on?
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- type of plate
- the direction the plates are moving relative to eachother |
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What are the three types of plate boundaries?
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divergent, convergent and transform
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What is a divergent plate boundary?
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a region where tectonic plates are spreading apart
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What are diverging plates?
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tectonic plates that are spreading apart
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What forms at divergent plate boundaries?
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ocean ridges and continental rifts
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Give an example of a well-known divergent plate boundary
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Mid-Atlantic Ridge is the longest on Earth and has the most volcanic activity
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What is a convergent plate boundary?
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a region where tectonic plates are colliding
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What are converging plates?
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tectonic plates that are colliding
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What happens during a Oceanic-Continental Plate convergence?
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- the oceanic plate subducts under the continental plate, forming a trench
- earthquakes can occur when pressure build-up between plates is released |
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What forms during a Oceanic-Continental Plate convergence?
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cone-shaped volcanoes, mountain ranges (when the continental crust crumples up)
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What is a trench?
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a deep underwater valley that is formed when an oceanic plate collides with a continental plate and is forced to slide beneath it
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What is a volcanic belt?
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a long chain of volcanoes
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What happens during an Oceanic-Oceanic Plate convergence?
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the cooler, denser plate will subduct under the other
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What forms during the Oceanic-Oceanic Plate convergence?
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volcanic island arc
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What is a volcanic island arc?
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a long chain of volcanic islands
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What happens in a Continental-Continental Plate convergence?
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- since densities are equal, no subduction will occur
- when they collide, plates fold and crumple |
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What forms from a Continental-Continental Plate convergence?
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mountain ranges
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Give a well-known example of a Continental-Continental Plate convergence mountain range
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Himalayas
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What are transform plate boundaries?
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plates move past each other due to convection currents in the mantle
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Where are transform plate boundaries found and what forms there?
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- found near ocean ridges
- no mountains or volcanoes form |
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What can commonly be found near or on transform plate boundaries?
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earthquakes and faults
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What are faults?
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large breaks in rock layers
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What are transform faults?
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faults that occur at a transform plate boundaries
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When do earthquakes form?
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when plates can no longer resist the build-up of pressure
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How have earthquakes affected British Columbia?
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- large earthquakes hit us every 200-800 years
- all 3 types of plate boundaries are found in or near us - 95% of earthquakes occur at tectonic plate boundaries |
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What is hard to predict about earthquakes?
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their timing, exact location and strength
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What is the focus?
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the location inside Earth where the earthquake starts
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What is the epicenter?
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the point on Earth's surface directly above the focus
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What are earthquakes classified by?
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depth of foci
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What happens when energy travels from a deep focus?
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an earthquake that is less damaging will result
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What happens when energy travels from a shallow focus?
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the earthquake will cause more damage
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What are seismic waves?
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vibrations caused by energy released by an earthquake
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What is seismology?
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the study of earthquakes and seismic waves
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What are characteristics of primary waves?
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- P
- type of body wave - first to arrive (fast) - ground squeezes and stretches in direction of wave travel - travels through solids, liquids, and gases |
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What are characteristics of secondary waves?
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- S
- type of body wave - second to arrive (slower) - ground motion is perpendicular to direction of wave travel - travels through solids but not liquids - (they do not travel through liquid outer core) |
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What are characteristics of surface waves?
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- L
- last to arrive (slow) - ground motion is a rolling action |
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How are earthquakes measured?
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using seismometers
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What are seismograms?
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records of ground motion
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What is magnitude?
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a number that rates the strength of an earthquake
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What does an increase of 1 magnitude mean?
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an earthquake is 10x stronger
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Compare the strength of a magnitude 6 earthquake to a magnitude 4 earthquake
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magnitude 6 earthquake is 100x more powerful than the magnitude 4 earthquake
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What does a distance-time graph show during an earthquake?
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the distance of the epicenter from an earthquake monitoring station
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What causes volcano formation?
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tectonic plate movement
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What are composite volcanoes/ stratovolcanoes?
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a large, cone-shaped volcanic mountain; the cone shape is the result of repeated eruptions of ash and lava
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What are characteristics of composite/stratovolcanoes?
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- large and cone-shaped
- belches smoke, ash and lava - found along plate boundaries - made of alternating layers of ash/cinder and lava - usually found near subduction zones |
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What are shield volcanoes?
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volcanoes that form over hot spots; the largest earthquakes on Earth
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What are characteristics of shield volcanoes?
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- form over hot spots (in ocean basins)
- made of gently sloping layers composed entirely of cooled lava - magma that forms shield volcanoes is thinner and traps less gas than the magma that makes composite volcanoes - largest in area out of the three main types of volcanoes - Hawaiian Islands are a chain of these volcanoes |
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What are rift eruptions?
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- occur through long cracks in the lithosphere
- fountains of lava erupt at spreading ocean ridges/continental crust - usually not very explosive, but release massive amounts of lava |
