Plate Tectonics- Key Terms Flashcards
What is the continental shelf?
The part of continental crust that extends into the sea past the land masses and forms a shelf like feature
What is tectonics?
The theory that tries to explain how the Earth is structured and what it is made up of
What is the crust?
The thinnest, top layer of the Earth made of the coolest, less dense rocks
What is the Big Bang?
The explosion of a star which threw out aggregation of materials which formed Earth
What is the mantle?
The mantle is from the bottom of the crust down to around 2900km. It surrounds the core and is mainly silicate rocks rich in iron and magnesium.
What is the core?
The core is at the centre of the Earth and made up of rocks rich in iron and nickel. There is a semi molten outer core and a solid inner core.
What is the lithosphere?
The lithosphere consists of the crust and rigid upper mantle. It is the zone where tectonic plates are formed.
What is the asthenosphere?
The asthenosphere consists of the semi molten part of the Earth’s mantle
What is Moho discontinuity?
The asthenosphere is 10% molten material so when seismic waves travel through it, they slow down and this is called Moho discontinuity.
What are primary (P) waves?
Primary (P) waves are the fastest seismic waves that arrive first and can travel through both liquids and solids. They are compressional waves so they vibrate in the same direction as they are travelling.
What are secondary (S) waves?
Secondary (S) waves travel at half the speed of P waves. They shake the ground from side to side and vibrate at right angles to the direction of travel.
What are surface (S) waves?
Surface (S) waves are unable to travel through liquids and are restricted to the Earth’s surface. They are much slower than secondary waves.
What are tectonic plates?
Tectonic plates are irregularly shaped rafts of lithosphere floating on the plastic asthenosphere underneath
What is continental crust?
Continental crust is usually over 1500 million years old. It is permanent and can extend beyond the margins of current land masses. It will not sink because of its’ lower density.
What is oceanic crust?
Oceanic crust is less than 200 million years old. It is much denser than continental crust and is continually being formed and destroyed at plate margins.
What are plate margins?
Plate margins are where two plates meet and either move towards eachother, away from eachother or past eachother.
What are convection currents?
Convection currents are circular movements of heat within the asthenosphere (upper mantle) which drive the movement of plates
What is continental drift?
Continental drift is the theory that originally all continents were joined together as a land mass called Pangaea and have drifted apart over time.
Who was Alfred Wegener?
Alfred Wegener was the first person to publish the theory of continental drift in 1912
What is meant by jigsaw fit?
Jigsaw fit is the fact that some continents appear to fit together like jigsaw pieces if they were put next to eachother e.g. Africa and South America
What is Pangaea?
Pangaea is an ancient supercontinent which originally joined together all the continents. It forms part of Wegener’s theory of continental drift.
What was a glossopteris?
Glossopteris is a fern that has been found in Africa, Antarctica, Australia and South America. It suggests that these continents were all once linked and had a similar climate.
What is a mesosaurus?
Mesosaurus is an extinct reptile that has been found in Africa and South America. It was a costal animal which could not have crossed the Atlantic Ocean- this suggests that these continents were once linked.
What is sea floor spreading?
Sea floor spreading is the theory that the Atlantic sea floor is spreading out from the centre at the speed of about 5cm per year
What is the Mid Atlantic ridge?
The Mid Atlantic Ridge is a ridge of mountains running along the middle of the Atlantic Ocean from which the sea floor appears to be spreading outwards.
What is paleomagnetism?
Paleomagnetism is the switching of the Earth’s magnetic field every 400,000 years which causes North and South to swap around, creating a pattern of magnetic stripes in rocks, which supports the theory of sea floor spreading.
Who were Vine and Matthews?
Vine and Matthews (1960s) were British geologists who discovered magnetic stripes running parallel to the Mid Atlantic ridge.
Who was Harry Hess?
Harry Hess (1962) was an American geologist who updated Wegener’s ideas by studying the age of rocks beneath the Atlantic. He found out that younger rocks were in the middle next to the ridge whereas older rocks (around 200 million years old) are further out from the centre which supports the idea of sea floor spreading
