BC Science 10 Chapter 12
Terms in this set (56)
The Continental Drift Theory
The continents have not always been in their present locations but have "drifted" there over millions of years.
Proof of The Continental Drift Theory
1. Continents fit together
2. Fossils: plants and animal fossils on different continents
3. Coal deposits (decomposition of carbon based life form) means there was life there at same point
4. Geology: Mountain ranges extend to other continents (ex. Appalachians)
5. Glaciation: erosional/depositional features of the land
-proposed continental drift theory
The Jigsaw Puzzle Fit
-South America's eastern coastline and Africa's western coastline fit together
-all continents were once joined together forming a "supercontinent" aka Pangaea
-mountain ranges that begin on one continent, end at the coastline then appear to continue on a continent across an ocean
-also similarities between rock structures, like: folds, rock age, etc
-ex: rocks found in Newfoundland are same type and age as rocks in Greenland, Ireland, Scotland, and Norway
-fossil findings of land animals in both South America and Africa
-clearly due to Pangaea because they could not have swum 6000km of open ocean between the two continents
-evidence of glaciers: U-shaped valleys, deeply scratched rocks, etc
-scientists were confused when they found evidence of glaciers in places that are now tropical areas...how could there be a glacier if the temperature is never below freezing?
-hence another piece of proof supporting continental drift theory
Refers both to the extent of ancient glaciers and to the rock markings they have left behind.
Large, movable slabs of rock.
-coal forms from the decomposition of once living things, usually tropical swamp material
-coal deposits were found in Antarctica which suggests that it had to once be in a tropical area, and therefore in a different position on Earth
Openings in Earth's surface that when active, spew out gases, chucks of rock and melted rock.
-composite or shield
A sudden, ground-shaking release of built-up energy at or under Earth's surface.
-after a collision at a subduction zone or transform plate boundary, frequent colliding can occur which resists the force of convection currents, ridge push, and slab pull
-pressure builds up as long as the plates remain stuck in place then when the stress is too great, energy is released and an earthquake occurs
-95% occur at tectonic plate boundaries
-80% occur in a ring bordering the Pacific Ocean
-Mountain range running north to south down the length of the Atlantic Ocean
1. Rock ages correspond on both sides of the ridge
2. Sedimentation thickness on both sides of the ridge
3. Magnetic striping - related to the core and movement of liquid
-describes magnetic reversal and the change of direction of the motion of liquid iron in the planet's interior
-this can make the Earth's magnetic north pole become the Earth's magnetic south pole (and vice versa)
Rock Ages Correspond on Both Sides of the Ridge
-samples of the ocean floor show that the youngest rocks were found closest to the ridge
-older rocks farther away from the ridge
-layer of ocean sediment became thicker the farther it was from the ridge
-thinner closer to the ridge
The small particles of silt and organic debris deposited on the ocean floor.
-pattern of stripes in the direction that iron containing minerals point on the sea floor
-repeated on both sides of the Mid-Atlantic Ridge
Sea Floor Spreading
-suggested that magma rises because it is less dense than the material that surrounds it
-magma cools and hardens when it breaks through Earth's surface at a spreading ridge, forming new sea floor
-as convection currents cause more heat to rise, new magma forces apart the hardened material and continuously pushes older rock aside
Molten rock from beneath Earth's surface.
Hess's Evidence of Sea Floor Spreading
1. Earth is like a large bar magnet and has two poles.
2. New ocean floor forms when magma 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 the basalt 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 cooled. Therefore, some portions of hardened rock will have normal polarity,, and others will have reverse polarity.
7. Rocks with magnetic striping, alternating bands of normal and revers 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. This is because the oldest rock is farthest from the ridge and has had the most time to accumulate sediments.
An area where molten rock rises to Earth's surface.
Made up of crust and the uppermost mantle which ranges in thickness from 65-100km.
Contain the dense rock basalt and crust can be 10km thick.
Contain large amounts of granite and crust can be 70km thick.
-Earth's outermost layer
-made from solid, brittle rock
-thickness and type of rock vary between type
-Earth's thickest layer: about 2900km thick: makes up 70 percent of Earth's volume
-two parts: upper and lower with transition zone between them at a depth of 660km
-composed of partly molten rock containing iron and magnesium
-magma flows like thick toothpaste
-made of solid, dense material that contains elements of magnesium and iron
-layer below mantle
-composed mainly of a mixture of iron and nickel
-sphere with a radius of about 1200km
-composed mostly of iron and nickel
-temperature ranges between 5000-6000 degrees Celsius
-however due to pressure it is still solid
-partly molten layer in upper mantle
-convection currents result as the the hotter and less dense material in the mantle rise, cool, then sink again only to be reheated
-this pushes the magma to Earth's surface causing tectonic plates to move and sometimes converge or diverge
The action of one plate pushing below another.
Areas of subduction that typically experience large earthquakes and volcanic eruptions.
A region where two tectonic plates are in contact.
Depends on the type of plate and the direction the plates are moving relative to one another.
3 types of plate interaction:
-Divergence: spreading apart
-Convergence: moving together
-Transform: sliding by
Divergent Plate Boundaries
Areas where plates are spreading apart.
Ex: Mid-Atlantic Ridge
Convergent Plate Boundaries
Occurs where tectonic plates collide.
Oceanic-Continental Plate Convergence
-oceanic plate is forced to slide beneath the continental plate
-trench forms where plates make contact
-magma can find way to surface and form cone-shaped volcanoes
Ex: a long chain of volcanoes of the west coast of North America are the result of oceanic-continental plate convergence between the Juan de Fuca Plate and the North American Plate aka the Cascadia subduction zone
-the force of the collision of plates creates mountain ranges as the continental rock crumples and folds
Oceanic-Oceanic Plate Convergence
-cooling causes one plate to be denser than the other then the denser plate slides into the mantle
-trench is formed
-convergence may produce a long chain of volcanic islands aka volcanic island arc
Ex: the Aleutian Islands
Continental-Continental Plate Convergence
-as plates collide, their edges fold and crumple forming great mountain ranges
Ex: Himalayas which formed as a result of the Indian and Asian continents colliding
Transform Plate Boundaries
-convection currents in mantle cause plates to slide by one another
-mostly occur near ocean ridges
-no mountains or volcanoes form
-earthquakes and faults can occur
Ex: The San Andreas Fault of California in USA due to the oceanic Pacific Plate sliding past the continental North American Plate
Breaks in the rock layers due to movement on either side.
-energy release begins at the focus
-focus: the location inside the Earth where an earthquake starts
-epicentre: the point on Earth's surface directly above the focus
How we measure the energy released from an earthquake.
Primary Waves (P)
-arrive first (approx 6km/s)
-moves through solid, liquid, or gas
-like a slinky
Secondary Waves (S)
-arrives second (approx 3.5km/s)
-only moves through solids
-moves up and down so is slow (technically travels longer distance)
-travels perpendicular to direction of wave
Surface Waves (L)
-travels on the surface of the Earth
-slow = 1.5km/s
ex. throwing a rock into the water. where it lands/hits water is the epicentre. The waves from it are surface waves
-ripples on a pond
-measures the amount of ground motion
-produces a seismograph showing
a) time of earthquake
b) how long it lasts
c) amount of shaking
How we feel Earthquakes
-how deep it is in ground or how near surface
-how much energy is released and how big
The strength of an earthquake = the amount of energy released
**with each step increase in magnitude, seismic wave is 10 x larger
-large cone-shaped mountains
-magma is very thick (flows slowly) and traps gas causing high pressure
-erupts when pressure is too great to be contained and is very explosive
-location: subduction zones
Ex: Mount Garibaldi, BC
-shield shape made from many lava sliding down sides after an eruption
-sides are not very steep
-magma is thin (flows easily) and traps little gas and oozes
-eruption is not very explosive
-location: hot spots
Ex. Kilauea, Hawaii
-occur when magma erupts through long cracks in the lithosphere
-curtain-like fountains of lava erupt at spreading ocean ridges or a rights in continental crust
-not very explosive or violent
-releases large amounts of lava