lesson 1: the structure of the earth

Question 1

the crust (four points)

Answer 1

• The crust is the Earth’s outermost layer and it’s where we live.
• It has an irregular thickness, varying from about 5 km beneath the oceans (oceanic crust)
• to about 30 km beneath the continents (continental crust).
• The crust mainly consists of lighter rocks, such as basalt in the oceanic crust and granite in the continental crust.

Question 2

the mantle (four points)

Answer 2

• Beneath the crust lies the mantle, extending to a depth of about 2,900 km.
• It contains silicate rocks that are rich in iron and magnesium.
• There are two sections of the mantle: the upper mantle, which is more rigid and behaves elastically on short time scales,
• and the lower mantle, which is solid but flows on geological timescales.

Question 3

the inner core (four points)

Answer 3

• The inner core is the central part of the Earth.
• It extends from a depth of about 5,150 km to the Earth’s centre at about 6,371 km.
• Although it is very hot, the inner core is solid due to the immense pressure at this depth.
• It’s composed primarily of iron, with minor amounts of nickel and other lighter elements.

Question 4

the outer core (3 points)

Answer 4

• The outer core extends from 2,900 km to about 5,150 km beneath the Earth’s surface.
• It mainly consists of liquid iron and nickel.
• the motion within this layer generates the Earth’s magnetic field.

Question 5

the lithosphere (four points)

Answer 5

• The lithosphere, about 10 to 200 km thick,
• includes the uppermost mantle and the crust.
• It’s rigid and breaks under stress, which is why it’s broken up into tectonic plates.
• The lithosphere varies in thickness, being thinner at oceanic ridges and thicker beneath older oceanic and continental regions.

Question 6

the asthenosphere (four points)

Answer 6

• Beneath the lithosphere, from about 100 to 350 km, lies the asthenosphere.
• The asthenosphere is the part of the upper mantle that exhibits plastic (or ductile) behaviour.
• The tectonic plates slide around on top of this layer.
• It’s composed of similar material to the rest of the upper mantle – mainly peridotite, a rock rich in silicate minerals.

Question 7

the mesosphere (four points)

Answer 7

• Below the asthenosphere and extending to about 2,900 km is the mesosphere
• lower mantle.
• The mesosphere is a region of strong, rigid rocks that deform slowly under the intense heat and pressure.
• It’s composed of silicate minerals that change in structure with depth due to increasing pressure.

Question 8

crust types

Answer 8

oceanic and continental

Question 9

oceanic crust

Answer 9

located underneath the ocean and is 5km thick. It is composed of basalt and is much denser than the continental crust

Question 10

continental crust

Answer 10

located underneath land masses and is 30km thick (median). It is composed of granite and is less dense than the oceanic crust