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Topic 7 - Does The Earth Move Beneath Our Feet > Part 3 > Flashcards

Part 3 Flashcards

1
Q

How might low sea level allow species to spread between continents?

A

Low sea level could expose dry land between continents removing the intervening ocean that was acting as a barrier to the natural spread of the species

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2
Q

What is the earths radius from the enter to the poles?

A

6357 km

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3
Q

What is the earths radius from the centre to the equator?

A

6378 km

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4
Q

What is the shape of the earth described as?

A

Oblate spheroid

Slightly flattened sphere

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5
Q

What distorts the earths shape?

A

It’s rotate

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6
Q

How does rigidity and density affect the speed of seismic waves?

A

Increasing rigidity acts to increase seismic wave speed, whereas increasing density acts to decrease it

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7
Q

What are seismic waves?

A

Vibrations from large earthquakes

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8
Q

What are seismometers?

A

They are sensitive vibration detectors that time arrivals of first vibrations at different distances from the known location of an earthquake

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9
Q

What is the deepest point in the ocean called and how many m deep is it?

A

It is called the challenger deep and it is 11034 m

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10
Q

What is the highest point about sea level called and how high is it?

A

Mount Everest 8848 m

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11
Q

Why is seismic speed halved when traveling through the earth?

A

Because the density of the core of the earth is about twice of the overlying mantle

So seismic speed is halved despite the greater rigidity of the mantle

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12
Q

What is the hard outer layer of the earth called?

A

The mantle

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13
Q

Is the outer part of the earths core solid?

A

Despite the immense pressure it is not solid

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14
Q

How many types of seismic waves concern us when dealing with the earths interior? And what are they called?

A

2 Types of seismic waves

Compressional wave (P wave)

A shearing wave (S wave)

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15
Q

What is a compressional wave also known as?

A

P wave

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16
Q

What is a shearing wave also known as?

A

S WAVE

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17
Q

Describe how a compressional (P) wave moves?

A

It is just like a sound wave in the air

It consists of alternate pulses of compression and dilation

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18
Q

Describe how a shearing wave moves?

A

It is an alternate side to side wobble traveling through the body of a material, rather like what happens inside a jelly of you shake it

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19
Q

What is the important distinction between compressional waves and shearing waves?

A

Compressional waves can travel through anything

Shearing waves can not pass through liquid as it offer no resistance to shearing motion

20
Q

How can we tell that the earths outer core is made of liquid?

A

Using a seismometer which can distinguish between the two types of waves, we can see that only P waves are transmitted through the outer core which must therefore be liquid

21
Q

Name the three main parts f the earths interior ?

A

Mantle (outer most)

Liquid outer core

Solid inner core

22
Q

What are the properties of the solid inner core of the earths interior?

A

The solid inner core has the properties we would expect of solid iron mixed with a few percent nickel.

It’s properties fits with other metals but iron core is the only reasonable one because t fits with the earth being rich in the same metallic as we find in the sun and meteorites

23
Q

What percentage of the earths liquid outer core is not metal?

A

It is thought to be about 10%

As it has a density too low to be pure metal

It is most likely composed of one of the relatively lighter elements like oxygen, carbon, hydrogen and potassium (however this has not been proved)

24
Q

How is the earths magnetism related to us thinking the core is made of iron?

A

The earth has a magnetic field that is believed to be the product of electrical currents generated by motion (a bit like dynamo) with the fluid outer core

To generate a field in this way, the zone responsible must be a good conductor of electricity and liquid (iron is but rock isn’t)

25
Q

What percentage of the earths core makes up its mass?

What percentage occupies the earths volume?

A

The earths core makes up 27.5% of its mass but its high density means that it occupies 10% of he earths volume

26
Q

What is the evidence that the mantle is not liquid?

A

S waves can pass though it

27
Q

What does the thickness of the continental crust vary between?

A

25 km in thin stretched regions

To as much as 90 km below the highest mountain ranges

28
Q

What does the thickness of oceanic crust vary between?

A

6-11 km

29
Q

What is the continental crust?

A

Underlying virtually all of land surface and the shallow sea out to the edges of the continental shelves

30
Q

What is the oceanic crust?

A

Forming the floor of the deep oceans

31
Q

What are the most abundant elements in crystal and mantle rocks?

A

Silicon and oxygen

32
Q

What is any comping made of chemical combinations of silicon and oxygen called?

A

Silica

33
Q

What are silicates?

A

Rocky materials dominated by silicon and oxygen but containing other elements too

34
Q

What is the moho?

A

The Moho is the interface between the denser l, silica poor rocks of the mantle and the less dense relatively silica rich rocks of the overlying crust

35
Q

Is oceanic crust denser than continental crust?

A

Oceanic crust is thinner and denser than continental crust

36
Q

What type of rock is most of the oceanic crust made of?

A

Igneous rock, generated by the solidification of formerly molten material( either erupted on the ocean floor as lave flows or injected in to the crust as intrusions)

37
Q

What type of rock is continental crust made of?

A

Some of it is igneous

There can be great thicknesses of sediment

Also contains metamorphic rock

38
Q

What rock type does the mantle of the earths interior have a chemical composition similar to?

A

Peridotite

39
Q

Why would it be impossible for the crust of the earth to slide around across the top of the mantle?

A

Because continental crust has deep roots that project in to it

The solution comes with recognition of layering based not on composition but on strength

40
Q

What do mountain belts need because the crust and underlying mantle do not have the strength to support them?

A

Buoyant roots

41
Q

What is the weakest point in the mantle or the earths interior and why do you think this is?
How deep down is it?

A

It is not immediately beneath the crust as you may think but around 100 km deep.

There is a slight drop of seismic speeds at this point

Which has been interpreted due to the presence of a few percent of molten material, however it must still be solid as S waves can still travel through it

42
Q

What is the weakest point in the mantle of the earths interior called?

A

Low speed layer sometimes low velocity layer is

43
Q

What does the weak zone of the mantle allow the outer shell of the earth to do?

A

It allows the outer shell to slide sideways across it

The outer shell is broken into large Slavs or plates

It is the sideways movement that enables continental drift to happen

44
Q

What is the lithosphere?

A

It is the uppermost part of the mantle and the continental crust/oceanic crust including the Moho

45
Q

What is the lithosphere mainly composed of?

A

Rocky material

46
Q

What is the asthenosphere?

A

It is the weak zone of the mantle which lies below the lithosphere

It is approximately 100km below the crust and includes the low speed layer

47
Q

Can you think of an everyday term that would describe something that does return to its original shape if deforming forces are removed?

A

The term elastic

You can stretch an elastic band but as soon as you relax the force it returns to its original shape

Topic 7 - Does The Earth Move Beneath Our Feet (6 decks)

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