C2 (1) Flashcards
What is the Crust?
A thin outer layer of solid rock
What is the Lithosphere? Properties?
Includes crust and upper part of mantle.
Made up of tectonic plates
Relatively cold and rigid
What is the mantle?
Near the crust = rigid
Deeper = flow slowly and less rigid and temp. increases
What is the core?
Inner core = solid
Outer core = liquid
What does radioactive decay cause in the mantle?
Convection currents which causes plates to move
What are tectonic plates?
Float on mantle
Move 2.5cm per year
Volcanoes and earthquakes often occur where plates meet
What are used to study the structure of the Earth?
Seismic waves
What are seismic waves used for?
To study the structure of the earth
How are seismic waves used to study the earth?
Measuring the time takes for waves to travel through earth and where they’re detected.
P?waves = through liquid and solid
S?waves = only in solids
What causes seismic waves?
Earthquakes or man made explosions on earth’s surface
What is Wegener’s theory? (1914)
Said that Africa and South America had previously been one continent that had split.
Continental drift” that there was once one supercontinent that has drifted apart.”
What evidence supported Wegener’s theory?
Matching rock layers on the different continents.
Same earthworms
Why wasn’t Wegener’s theory accepted at first?
The movement wasn’t detectable and the drifting” explanation wasn’t convincing.”
What new evidence was found in 1960? (Sea floor spreading)
Scientists investigated mid?atlantic ridge.
Evidence that magma rises up through sea floor, solidifies and forms underwater mountains that are roughly symmetrical either side of the ridge. (Suggests that sea floor is spreading)
What new evidence was found in 1960? (Rocks)
The magnetic oritentation of rocks.
As magma erupts through gap, iron particles in rocks align with magnetic field. The magnetic field swaps direction and rock either side of the ridge has bands of magnetic polarity.
What causes volcanoes to occur?
When molten rock (magma) from the mantle emerges through the Earth’s crust
What is subduction?
When a dense oceanic plate is forced under a less dense continental plate
How do oceanic and continental plates colliding cause volcanoes?
The oceanic plate is forced under continental
Oceanic plate is cooler at edges so they sink easily, pulling the plate down
As it is forced down the oceanic crust melts and starts to rise.
If the molten rock comes to the surface = volcano
What rocks are made from molten rock cooling down and solidifying?
Igneous rocks
What does the type of igneous rock made depend on?
How quickly the magma cools
The composition of the magma
When is an eruption fairly safe?
If the magma forms iron?rich basalt and the lava from the eruption is runny
When is an eruption explosive?
If the magma is silica?rich rhyolite. Thick lava is produced which can be violently blown out the volcano
Why is it hard to predict the eruptions of volcanoes?
They are very unpredictable
Scientists can only say more than normal to happen not that its certain
How are sedimentary rocks formed?
?Formed from layers of sediment in lakes or seas
?Over millions of years layers get buried under more layers ad the weight of this squeezes the water out
?Fluids flowing through the pores deposit natural mineral cement
What is limestone formed from?
Seashells = calcium carbonate
What is produced when limestone (CaCO3) thermally decomposes?
Calcium oxide and carbon dioxide
CaCO(3) = Ca0 + C0(2)
How are metamorphic rocks formed?
By the action of heat and pressure on sedimentary or igneous rocks over long periods of time
Eg. Marble formed from limestone
How are igneous rocks formed?
When magma cools