Earth Science Plates - Unit 2

Why do Continents move?

· Plates move on a layer of partially molten rock. · Heat from the Earth's core cause convection currents in the mantle · Hot rock rises towards the surface, spreads in 2 directions a go sideways (earth's crust is very slowly dragged apart) · That means the crusts, plates slowly move continents · NOTE: crust can be slowly · Constructed (e.g. in Atlantic Ocean) or · Destroyed (e.g. in Pacific Ocean) · The currents slowly move the crusts around · In some places, the crust is slowly destroyed and on other places, new crust is formed

Seafloor Spreading

movement of two oceanic plates away from each other, resulting in formation of new oceanic crust and a mid-ocean ridge

Plate Tectonics

theory that Earth's surface is made up of huge sections that are continually moving

What are hotspots?

- A place deep within the Earth where hot magma rises to just underneath the surface, creating a bulge and volcanic activity - Often the hot spot creates a chain of volcanoes, as a plate moves across a relatively stationary mantle plume.

Tectonic Plates:

- Earth has a diameter of approximately 6000km - The core and mantle have remained hot - The mantle is in a molten state - Earth's surface, however, radiates heat out into space thus the surface skin is cool enough for rocks and minerals to solidify and insulate us from the heat of the mantle - Earth's crust is only between 7km and 50km thick and can be visualized with the analogy of a cracked eggshell - Wegener's Theory of Continental Drift which stated that all the continents were once joined as the supercontinent Pangaea, is newly replaced with 'Tectonic Plate Theory'

Magnetic Stripping

- Earth's magnetic field reverses every 300, 000 years or so as shown by the flipping compass (N-S) & (S-N) - An alternate band of rock formation appears - This is because older rocks move outward and newer rocks form at the plate boundary.

Sometimes plate movement causes two continents to collide. Which two processes are most likely to occur as a result of this collision?

- Earthquakes - High mountain ranges

Name a country that is famous for hot spots.

- Hawaii - Iceland - Galapagos Islands

Oceanic Crust

- Located beneath deep ocean - Very thin, between 5km and 8km - (basalt) Younger, more dense , heavier than continental

Continental Crust

- Located beneath land masses and under shallow seas - Very thick - between 30km and 60km - Mostly granite - but also sedimentary, metamorphic - Old, thicker, less dense than ocean crust and mantle (floats on mantle)

Types of crusts and problems with Continental Drift

- Mafic igneous rocks have a harder, more dense composition of iron and other metals - Sedimentary rocks are the result of weathering and contain more silicates (like sand) and aluminium and different lower density, mostly non-meal elements. - Felsic igneous rock often results from melting and reforming of sedimentary rock, therefore, made of less dense minerals. - The cooling of magma and lava forms igneous rock. Oceanic crust is much thinner and composed mostly of hard, dense mafic rock. - Continental crust may have experienced erosion over a long time and contains more sedimentary and felsic igneous rocks which are both less dense and softer.

When heat is applied to a substance the particles of the heated substance: (hint. 3 things)

- Move faster - Rebound off each other with more faster - Spread out more The particles themselves don't change size with heat but the additional space between particles means that there will be a smaller number of particles per unit of volume is called DENSITY. Therefore, Heating a substance lowers its density.

Oceanic Colliding with Continental

- Subduction occurs - Oceanic crust sinks as it is denser than the continental crust. - This causes powerful earthquakes and volcanoes When an oceanic plate collides with a continental plate, the edge of the oceanic plate is forced down into the mantle. This process is called "subduction"

Plates and Crust

- The Pacific Plate is entirely made of oceanic crust - The North American Plate is made of oceanic and continental crust - If crust is, the outer shell of the earth, the plates are the section that move because of convection in the mantle

Hawaiian Islands

- The best example of a hot spot volcanic chain is the Hawaiian Islands - The chain of Hawaiian Island is though to have been created by the movement of a tectonic plate over a hot spot

San Andreas Fault

- The boundaries between sliding plates like the San Andreas Fault in the U.S. are known as conservative plate boundaries. The solid crust is neither created nor destroyed at these boundaries. - The San Andrea Fault is perhaps the best-known example of a boundary between sliding plates - Although both plates are moving in a north westerly direction, the Pacific Plate is moving faster than the North American Plate, so the relative movement of the North American Plate is to the south east. The Pacific Plate is being moved north west due to sea floor spreading from the East Pacific Rise (divergent margin) in the Gulf of California. The North American Plate is being pushed west and north west due to sea floor spreading from the Mid Atlantic Ridge (divergent margin). - Movement along the fault is not smooth and continual, but sporadic and jerky. Frictional forces lock the blocks of lithosphere together for years at a time. When the frictional forces are overcome, the plates slip suddenly and shallow focus earthquakes are generated. Landscape and manmade features (eg rivers, fences and roads) are displaced across the fault as movement occurs. San Francisco has historically suffered significant earthquakes, notably in 1906 and 1989. - The average rate of movement along the San Andreas Fault is between 30mm and 50mm per year over the last 10 million years. If current rates of movement are maintained Los Angeles will be adjacent to San Francisco in approximately 20 million years.

What were the three explanations about continental drift theory?

- The continents fit together like a jigsaw puzzle - The continents were floating and drifting on a denser material below - They were breaking apart and re-joining in a process that is called continental drift

When 2 Continents Collide

- They push against each other - Vast mountain ranges are formed - like the Himalayas - Neither is subducted easily because of their similar density's - As mantle convection presses the continents together, they crush each other and rock is buckled and forced upward

Places where Diverging Plate Boundaries Exist

1. East Africa- Africa and Middle East with Red Sea in the middle 2. Iceland divided into two parts as it sits on the divergent boundary - in the middle is Mid-Atlantic Ridge

Plates

1. North American 2. South American 3. African 4. Eurasian 5. Pacific 6. Indo-Australian 7. Antarctic

The theory of plate tectonics explains the movement of, and changes to, the Earth's crust. The key points are:

1. The Earth's surface is made up of several huge tectonic plates (like pieces of a jigsaw puzzle) that are continually moving. 2. The ocean floors are continually moving, spreading from the centre and sinking at the edges 3. Earthquakes and volcanoes occur at plate boundaries, where the tectonic plates meet. Convection currents in the mantle move the tectonic plates on the Earth's surface. The source of the heat driving the convection

What surface feature would you expect at a divergent boundary?

A Mid-Ocean Ridge

Convergent Plate Boundary

A convergent boundary is where two tectonic plates collide into each other. 1.An oceanic plate and continental plate colliding (known as subduction) 2. Two oceanic plates can collide 3. Two continental plates can collide (forming mountains) When two continents meet head-on, neither is subducted. Instead, the crust tends to buckle and be pushed upwards or sideways.

Divergent Plate Boundary

A divergent boundary occurs where two tectonic plates separate and move away from each other (diverge). Regardless of where they occur, divergent boundaries all have one thing in common. Where a gap opens in the Earth's crust, magma rises to the surface and becomes solid.

Explain the difference between a dormant volcano and an extinct volcano.

A dormant volcano is an active volcano that is not erupting, but supposed to erupt again. An extinct volcano has not had an eruption for at least 10, 000 years and is not expected to erupt again in a comparable time scale of the future.

What is a fault and how is one formed?

A fault is a crack in the rocks along which movement occurs. It results from massive compressive or stretching forces exerted on the rocks by the movement of the plates.

What is a divergent boundary?

A plate boundary where two plates move away from each other.

Transform Plate Boundary

A tectonic boundary, where two plates slide past each other. Transform boundaries are places where plates slide sideways past each other. At transform boundaries lithosphere is neither created nor destroyed. Many transform boundaries are found on the sea floor, where they connect segments of diverging mid-ocean ridges. California's San Andreas Fault is a transform boundary - Both the plates can move in opposite direction, or same direction but at different speeds - Cracks in layers of rock are called fault lines. Fault lines are often caused by the relative movement of the underlying tectonic plates. - Even when the sliding is smooth, small earthquakes occur - More severe earthquakes occur when something prevents the plates from sliding - Pressure builds up until there is enough force to restart the sliding with a jolt - Friction is eventually overcome, and the plates slip past in a sudden movement. The shockwaves create to produce an earthquake.

Explain the events that occur at a transform boundary.

AS the two plate move along, friction builds up and the rocks get caught up, when the tension is released it cause the land to suddenly shake causing an earthquake

Name of the person who proposed the theory of Continental Drift?

Alfred Wegener

Mantle Plumes

Areas of hot, up-welling mantle. A hot spot develops above the plume. Magma generated by the hot spot rises through the rigid plates of the lithosphere and produces active volcanoes at the Earth' surface. AS oceanic volcanoes move away from the hot spot, they cool and subside, producing older islands, atools and seamounts. As continental volcanoes move away from the hot spot, they cool, subside and become extinct.

Describe and explain reasons for the relationship between depth of the earthquakes and the distance from the plate boundary.

As earthquakes mostly occur where tension is released on the rubbing surfaces of the two plates, they trace out the shape of the top surface of the subducting plate. The shallowest earthquakes occur closest to the plate boundary as this is where the plate has only just begun to submerge. The further from the plate boundary, the lower the longitude and the deeper the earthquake.

Mount Gambier is an example of an extinct volcano while Mount Pinatubo is an example of an active volcano.

Ash is a solid material ejected by an eruption, while water vapour and hydrogen sulphide are gases.

Why does oceanic crust subducts rather than the continental crust.

Being mostly dense, mafic igneous rock, oceanic crust sinks more easily when forced than the relatively buoyant sedimentary rock of continental crust.

Which of the 4 main layers is solid? (hint. 2 answers)

Crust and Inner Core

Define a hot spot

Deep within the Earth where hot magma rise to just underneath the surface, creating a bulge and volcanic activity.

Plate Motion - Sliding

Description - Plates are sliding laterally past each other in different directions

Plate Motion - Subducting

Description - The edge of an oceanic plate is sliding under a continental plate

Plate Motion - Spreading

Description - plates are moving away from each other

Mountain Ranges

Discovery of mountain ranges on different continents

Fossil Distribution

Discovery of similar fossils of plants and animals on different continents

What type of boundary forms two neighbouring plates move apart from one another?

Divergent

The Yellowstone hot spot

Has been active at least 15 million years, producing a chain of calderas and volcanic features along the Snake River Plain that extends 650km westward from northwest Wyoming to the Idaho-Oregon border.

The theory of plate tectonics explains:

How continents and oceans move and change over long periods of time.

Explain why IcIeland is comped of dense rock like Oceanic Crust while Africa's Rift Valley is in Continental Crust.

Iceland was formed in the middle of the ocean by volcanic activity of the oceanic crust, whereas Africa is part of the continental crust.

Which layer has the greatest temperatures and pressures?

Inner core

What are the four main layers of the Earth?

Inner core, outer core, mantle and crust

"The tallest peak in the Himmalays, Mount Everest, is CURRENTLY 8, 848 metres tall."

It says currently because they are still converging-colliding or pushing each other and therefore the height of the mountain range is still increasing

Atmosphere

Layer of gases surrounding Earth, to a height of approximately 145km. Made up of gases such as nitrogen and oxygen.

Outer Core

Molten iron and nickel. Temperatures mostly between 4000°C and 6000°C. About 2300km thick.

The lava moving from a volcano can be runny like a milkshake or pasty like toothpaste.

Molten rock that has not reached the surface of the earth is called magma.

Inner Core

Mostly iron. Solid owing to extreme pressure. Temperatures up to 7000°C. About 1200km.

Identify one convergent boundary

Nazca and South American Plates

Why do you think Volcanoes are far less common at transform plate boundaries?

No room for the magma to come up

Subduction Zones

Occur when converging crusts force one of the crusts downward. If one of the crusts is continental its buoyancy will always ensure that it stay on top When oceanic meets oceanic crust meets oceanic then whichever crust is, more dense will be pushed under

Which crust subducts in a subduction zone and why?

Oceanic crust subducts as it is denser.

Which of the four main layers of the Earth is liquid and composed mainly of iron and nickle?

Outer core

Mantle

Partially molkten rock. Temperatures mostly between 500°C and 2000°C. About 2900km.

Hot Spots

Places within the mantle where rocks melt to generate magma. The presence of a hot spot is inferred by anomalous volcanism (i.e. not at a plate boundary), such as the Hawaiian volcanoes within the Pacific Plate. The Hawaiian hot spot had been active at least 70 million years, producing a volcanic chain that extends 6000km across the northwest Pacific Ocean. Hot Spots also develop beneath continents. The Yellowstone hot spot has been active at least 15 million years, producing a chain of calderas and volcanic features along the Snake River Plain that extends 650km westward from northwest Wyoming to the Idaho-Oregon border.

Define Transform Boundary

Plate boundary where the edges of two plates slide past each other, either moving in the same direction with different speeds or in opposite directions

Explain the plate tectonics theory.

Plate tectonic theory suggests that the Earth's crust is not a uniform unbroken covering, but is divided into a number of 'plates'. These plates move on a layers of partially molten rock in the upper mantle. The movement is due to convection in the mantle.

What is a transform boundary?

Plates slide past each other

Shape of the continents

Shape of the continents - they fitted together

Australian Plate Theory

Since the fragmentation of Gondwanaland, the configuration of the Australian plate has undergone several substantial dramatic changes in terms of the configuration of its plate boundaries including, most dramatically, the amalgamation of the Indian and Australian plates to form the present configuration of the Indo-Australian Plate.

What type of fault is the San Andreas Fault?

Slip or transform boundary

Crust

Solid rock . Varies in thickness from as little as 5km under the ocean to about 70km under mountain ranges such as the Himalayas. Thin, rocky, outer layer of the Earth.

What happens at a convergent boundary?

Subduction occurs, volcanoes, trenches and fold mountains

Boundary Type - Transform

Surface Feature - Earthquake Faults Earthquakes - Shallow to Medium

Boundary Type - Divergent

Surface Feature - Mid Ocean Ridges Earthquakes - Shallow Depths Only

Boundary Type - Convergent - subduction - collision

Surface Feature - Volcanoes, trenches, high folded mountains Earthquakes - Shallow to deep. All Depths

Explain the process that leads to an earthquake occurring at a transform boundary.

Tension builds up

Why do volcanoes make a 'ring of fire' around the Pacific Ocean?

The 'ring' is a giant weakness in the Earth's crust.

Glacial evidence determined from rock evidence

The continents used to be closer to South Pole

What is the difference between continental drift and tectonic theory?

The difference between continental drift and plate tectonics is that the theory of continental drift states that the world was made up of a single continent. The theory of plate-tectonics, on the other hand, states that earth's surface is broken into numbers of shifting plates or slabs.

Explain the events that occur at a subduction zone

The edge of both the plates are dragged downwards and the subducting plate melts as it enters the mantle causing a volcano. Also when the plates are dragged downwards, tension builds up as rocks get caught, when the tension suddenly releases, it causes an earthquake.

Key Points

The theory of plate tectonics explains the movement of, and changes to, the Earth's crust. - Earth's surface is made up of several huge tectonic plates (like pieces of a jigsaw puzzle) that are continually moving - Ocean floors are continually moving, spreading from the centre and sinking at the edges - Earthquakes and volcanoes occur at plate boundaries, where the tectonic plates meet - Convection currents in the mantle move the tectonic plates on the Earth's surface. The source of the heat driving the convection currents is radioactive decay deep within the Earth's core.

In which layer does convection current occur?

The mantle

How can something as large as a continent move?

The movement of continents can be explained by continental drift. The continents move on the plates that the Earth's crust is divided into.

Coal seams in Antarctica

The vegetation that formed into coal indicated that Antarctica wasn't always in the South Pole as no vegetation would have survived the cold weather

Alfred Wegener proposed the theory of continental drift. This is the idea that the continents are not stationary but move around Earth's surface. (true or false?)

True

Name the event that occurs as a result of hot spots.

Volcanoes

How can a volcano suddenly appear from nowhere?

Volcanoes are formed when molten rock from the Earth's mantle bursts through a weakness in the Earth's crust.

Hydrosphere

Water on or at the Earth's surface, including oceans,lakes, rivers, rain and mist

Continental Drift Theory was not widely accepted when it was first proposed because:

Wegener couldn't explain why or how the continents move

Plate Boundary

area where tectonic plates meet, interact, affect Earth's surface

Ocean Trenches (formed from converging oceanic plates)

When the ocean floor was being mapped out in the 1950s and 1960s, not only were mid-ocean ridges discovered, at other plate boundaries very deep ocean trenches were found. These trenches can go down more than 12km under the surface of the ocean. Ocean trenches are the result of converging tectonic plates. When a plate is forced down into the mantle it melts. This balances out the mass of new crust formed at diverging plate boundaries.

Define Subduction Zone

When two plates collide, the more denser one sinks underneath the less dense plate

What is a convergent plate boundary?

When two plates collide/push against each other.

Formation of the Himalayas

While mountains can be formed by volcanic lava, the highest mountains in the world are the fold mountains such as the Himalayas between India and the rest of Asia. On top of the Himalayas ocean fossils can be founds indicating that his rock used to be lower than sea level.

Describe how the movement of the India plate is different to the movement of other plates.

While other plates are moving away from each other, the Indian Plate is still moving into Asia.

Do we have Earthquakes in Australia? Why?

Yes. Australia is not situated at the boundary of the plate but instead sits in the middle of it. Since that plate is moving constantly but slowly, it is under pressure, this causes tension in certain parts of the tectonic plate when it is converging with other plates, so from time to time, it suddenly shakes and we do get small Earthquakes.

Assuming that continental drift will continue, a map of the world one billion years from now would probably show...

a radically different arrangement of continents and oceans.

Which of the following plates are divergent? (hint. 2 answers) a. South American and African Plates b. Nazca and Pacific Plates c. Nazca and South American Plates d. Indian and Eurasian Plates

a. South American and African Plates b. Nazca and Pacific Plates

What is likely to form at the boundary between the Nazca and Pacific Plates? a. High Mountain Range b. Mid-Ocean Ridge c. Rift Valley d. Ocean trench

b. Mid-Ocean Ridge

Consider the boundary between the South American and African Plates. The ocean here is currently.... a. staying the same size because it occupies a single stable plate b. getting smaller as the two plates move together c. getting bigger as the two plates spread apart

c. getting bigger as the two plates spread apart

What is the lithosphere? a. this is just another name for the crust b. this is just another name for the mantle c. a layer of the mantle that is partially melted d. the crust and the rigid upper layer of the mantle

d. the crust and the rigid upper layer of the mantle

Tectonic Plate

one of the huge section of the Earth's surface that moves slowly over the mantle

Tectonic plates are...

slabs of the lithosphere.