Plate Tectonics Flashcards
What are Tectonic plates?
- Plates are rigid, rocky sheets that ‘float’ on the surface of the Earth – process is called ISOSTASY
- They lie on top of underlying ‘plastic’ magma in the Earth’s mantle
Where do the most earthquakes occur?
- Most earthquakes occur along the edge of the oceanic and continental plates.
How many plates are there?
- The earth’s crust is made up of several pieces, called plates. The plates under the oceans are called oceanic plates and the rest are continental plates
What are the major Tectonic plates?
The lithosphere is broken up into seven major plates:
- African plate
- Antarctic plate
- Eurasian plate
- Indo-Australian plate
- North American plate
- Pacific plate
- South American plate
Study the diagram of the Earth’s Plates
https://docs.google.com/document/d/11SlS_6djE3BGAezT2-FeVRTdxG1P1jVyj-u3X2L5qDo/edit?usp=sharing
What is the structure of tectonic plates?
- Plates are made of a layer of the Earth called the Lithosphere
- The Lithosphere is a combination of the Crust plus the upper solid mantle
- The Lithosphere ‘floats’ on the underlying Asthenosphere
What is the Asthenosphere?
- The upper layer of the earth’s mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur
What are the main components of the lithosphere?
- The lithosphere is made up of rocks from two of the Earth’s major layers. It contains all of the outer, thin shell of the planet, called the crust, and the uppermost part of the next-lower layer, the mantle
What is the Earth’s mantle and crust mainly composed of?
- Earth’s mantle is made up of rock containing silicon, iron, magnesium, aluminium, oxygen and other minerals.
- The crust, is made up of mostly oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium
What causes the convection currents of magma?
- Earth’s core is very hot
- Earth’s Lithosphere is cold
- We get convection currents as hot magma rises to the Earth’s surface, cools and then sinks back down
- The end result is – plates are not static, they are mobile
How do the magma convection currents work?
- Molten lava from the mantel rises, heated by the Earth’s core
- Near the surface the rock spreads in two direction and goes sideways.
- As it gets closer to the surface it begins to lose heat and eventually the much cooler rock sinks back down
What causes the continents to move?
- Through the convection currents the spreading process of the Earth’s crust is very slowly dragged apart and it’s this that ultimately causes the continents to move
What do volcanoes release?
- Where the plates collide, the rock on the seafloor containing carbon from the dead plankton is carried deep into the Earth
- As it descends, this layer of rock is heated so the rock melts, releasing carbon dioxide and thus, gas is returned back into the atmosphere during an eruption
What is Continental Drift?
- The continents look like a jig saw puzzle
- This is because plates slip and slide or ‘drift’ past each other and have been moving around very slowly since the Earth differentiated.
When was the Continental Drift theory proposed?
- The theory of Continental Drift isn’t that old – proposed by Alfred Wegener in 1910’s and only widely accepted in 1960’s
List some of the super continents and how long ago they were formed
- Vaalbara (3300 MYA)
- Ur (3000 MYA)
- Kenorland (2750 MYA)
- Arctica (2500 MYA)
- Atlantica (2093 MYA)
- Atlantica/Nena (1827 MYA)
- Columbia (1816 MYA)
- Rodinia (1127 MYA)
- Pannotia (745 MYA)
- Gondwana (567 MYA)
- Pangaea (328 MYA)
- Gondwana/Laurasia (151 MYA)
- Laurasia (134 MYA)
What is Palaeomagnetism?
- Palaeomagnetism is the study of the record of the Earth’s magnetic field in rocks, sediment, or archeological materials. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form
When was the theory of continental drift accepted?
- The theory of Continental Drift was only widely accepted with a type of geophysical evidence called Palaeomagnetism
How is Palaeomagnetism used to prove continental drift?
- The Earth is a big magnet, hence, North Pole and South Pole
- Every few million years the direction of the poles switches
- Rocks with magnetic minerals (i.e., iron) lock in the prevailing magnetic direction
How is Palaeomagnetism evidence for plate movement?
- As rocks move away from certain types of plate boundaries, they lock in a magnetic signature which is symmetrical on both sides of the boundary
- Example on the google doc
What are plate boundaries called and how many different types are there?
Plate boundaries are called ‘margins’ and there are 3 main types:
- Divergent
- Convergent
- Transform
What is the Divergent type of plate boundary?
- A divergent plate margin is where the two tectonic plates are moving away from each other
What is the Convergent type of plate boundary?
- A convergent plate margin is where the two tectonic plates are moving toward each other
What is Subduction?
- When continental and oceanic plates collide, the thinner and more dense oceanic plate is overridden by the thicker and less dense continental plate. The oceanic plate is forced down into the mantle in a process known as “subduction.”