C2 Flashcards
What is the crust?
The earths thin outer layer of solid rock
What is the average depth of the core?
20km
What is the lithosphere?
It includes the crust and the upper part of the mantle, it is made up of a jigsaw of ‘tectonic plates’
Give two properties of the lithosphere
It is relatively cold and rigid
It is over 100km thick in places
What is the mantle?
The solid section between the crust and the core
What happens as you get closer to the mantle?
The temperature increases
As the temperature increases what happens to the mantle?
It becomes less rigid
It can flow very slowly
It behaves like a semi-liquid
Give a property of the core
It is just over half the Earth’s radius
Give a property of the inner core
It is a solid
Give a property of the outer core
It is a liquid
What are convection currents?
The heat from the core rises up and causes the magma to go towards the crust, as the cool magma from higher up falls closer to the core. This causes currents in the magma to move the tectonic plates of the lithosphere to move.
Why do the tectonic plates float on the mantle?
Because they are less dense than the mantle
What happens to the continents when the plates move?
The continents move too
How much do the plates move each year?
2.5 cm
What happens when the plates meet?
Volcanoes and earthquakes
Why can’t you get to the inner structure of the earth directly?
Because the crust is too thick to drill through
What waves to scientists use to study the Earth’s structure?
Seismic waves (shock waves)
How can seismic waves be produced?
Earthquakes
Big man-made explosion at the earth’s surface
How can scientists draw conclusions about the structure of the earth?
By measuring the time that it takes for seismic waves to travel through the earth, and finding out where they are detected.
What are the two types of seismic waves?
S-waves
P-waves
What can P-waves travel through?
Solids and liquids
What can S-waves travel through?
Solids only
S-waves can travel through the mantle which means that it is _____.
Solid
S-waves are not detected in the core’s shadow, so the outer core must be _____.
Liquid
P-waves travel faster through the middle of the core, which suggests that the inner core is _____.
Solid
When has the idea that they Earth’s surface is made up of moving plates of rock been around from?
The early twentieth century
Fossils of similar plants and animals have been found on opposite sides of the Atlantic ocean, why did most people in the past think this was?
They thought that the continents had been linked by ‘land bridges’ which had sunk or been covered by water as the earth cooled.
What things puzzled people, regarding the Earth’s structure?
Why the coastlines of Africa and South America fit together
Why there are fossils of sea creatures in the Alps
In 1914 who hypothesised that Africa and South America had once been one continent?
Alfred Wegener
What evidence did Alfred Wegener find to back up his hypothesis?
There were matching layers in the rocks on different continents
There were similar earthworms living in both South Africa and South America
What did Wegener’s theory of ‘continental drift’ suppose?
It supposed that about 300 million years ago there had been one ‘supercontinent’ - which he called Pangaea
According to Wegener, Pangaea broke into smaller chunks and these chunks (our modern day continents) are slowly drifting apart.
Why wasn’t Wegener’s theory accepted at first?
It was a big change and the reaction from other scientists was hostile
His explanation of HOW the ‘drifting’ happened wasn’t convincing
The movement wasn’t detectable
He claimed the movement could be caused by tidal forces and the earth’s rotation
But other geologists proved the later was impossible
In what decade did scientists investigate the Mid-Atlantic ridge and why was this significant?
1960s
They found evidence that magma rises up through the sea floor, solidifies and forms underwater mountains.
This suggested that the sea floor was spreading at about 10cm per year and thus supported Wegener’s theory
Where did even better evidence that the continents were moving apart come from?
The magnetic orientation of the rocks.
Give evidence for the magnetic field of the Earth expanding and swapping directions
The rock on either side of the ridge had bands of alternative magnetic polarity.
These are symmetrical about the ridge.
How do volcanoes occur?
Molten rocks (magma) from the mantle emerges through the Earth's crust. Magma rises up (through the crust) and 'boils over' where it can erupt. This can sometimes be quite violent if the pressure is released suddenly.
What is the difference between magma and lava?
Molten rock below the earths surface is called magma
When it erupts from a volcano, it’s called lava.
Which is denser? The crust on the ocean floor or the crust below the continents?
The crust on the ocean floor
What is subduction?
When two tectonic plates collide, a dense oceanic plate will be forced underneath a less dense continental plate.1
Finish the sentence:
Oceanic crust tends to be ____ at the _____ of a tectonic plate - so the edges _____ easily, ______ the oceanic plate _____
cooler edges sink pulling down
What happens to the oceanic crust in subduction?
It is forced down, melts and starts to rise. When this molten rock finds its way to the surface, volcanoes form.
What is igneous rock?
It is made when any sort of molten rock cools down and solidifies.
What does the type of igneous rock depend on?
How quickly the magma cools
The composition of the magma
Is a volcano fairly safe or not if the magma produces iron-rich basalt?
Yes, the lava from this eruption is runny meaning it is fairly safe
Is a volcano fairly safe or not if the magma produces silica-rich rhyolite?
No, this means that they eruption is explosive. It produces thick lava which can be violently blown out of the top of the volcano.
Give an example of a way that scientists can detect if a volcano is going to erupt
If there is magma movement below the ground, near to a volcano
What are the three different types of rock?
Sedimentary
Metamorphic
Igneous
How are sedimentary rocks formed?
From layers of sediment laid down in lakes or seas
Over millions of years the layers get buried under more layers and the weight pressing down squeezes out the water.
What type of rock is limestone?
Sedimentary
What is limestone mostly formed from?
Seashells, calcium carbonate.
What happens to limestone when it is heated?
It thermally decomposes to make calcium oxide and carbon dioxide
Write a symbol equation for the thermal decomposition of limestone
CaCO3 (s) —> CaO (s) + CO2 (g)
How are metamorphic rocks formed?
They are formed by the action of heat and pressure on sedimentary (or even igneous) rocks over long periods of time.
Finish this sentence:
As long as the rocks don’t actually ___ they’re classed as __________ rocks.
melt
metamorphic
What happens if metamorphic rocks melt?
They turn into magma and are gone. They may eventually re-surface as igneous rocks.
What type of rock is marble?
It is a metamorphic rock formed from limestone
Out of marble, limestone and granite, label them in order of hardness rating from most hard to least hard.
Granite
Marble
Limestone
How does limestone turn into marble?
They are made of the same chemicals
Very high temperatures and pressures break down the limestone and it reforms as small crystals
This gives marble a more even texture and makes it much harder.
How are igneous rocks formed?
When magma cools
Why are igneous rocks very hard?
Because they contain various different minerals in randomly arranged interlocking crystals.
What is granite ideal for?
Steps and buildings
What are ores?
Minerals we can get useful materials from
Give two examples of construction materials that can be extracted from ores
Aluminium and iron
How is glass made?
By heating up limestone (calcium carbonate), sand (silicon dioxide) and soda (sodium carbonate) until it melts.
What is clay?
It is a mineral formed from weathered and decomposed rock.
How is clay made into bricks?
Dug from the ground, soft
Moulded into shape
Hardened by firing at very high temperatures
What does clay contain?
Aluminium and silicates
How is cement made?
Powdered clay and powdered limestone are roasted in a roasting kiln to make a complex mixture of calcium and aluminium and silicates