3.1.5.2 Plate tectonics

Question 1

Describe features of the core

Answer 1

• Made up of dense rocks containing iron and nickel alloys
• Divided into a solid inner core and a molten outer one
• Over 5000 degrees C

Question 2

How is heat produced in the core?

Answer 2

Primordial heat - left over from the Earth’s formation
Radiogenic heat - produced by the radioactive decay of isotopes present in the core such as uranium and potassium

Question 3

Describe features of the inner core

Answer 3

• 1200 km thick
• Mainly nickel and iron
• Even though temperature is high, pressure is so high the molecules cannot flow past each other

Question 4

Describe features of the outer core

Answer 4

• around 2300 km thick - thicker than inner core
• Temperatures high enough that nickel and iron can melt
• Pressures low enough that they can still be in a fluid state
• Liquid outer core
• Low viscosity
• it is thought that the liquid outer core spins creating the `earth’s magnetic field

Question 5

Describe features of the mantle

Answer 5

• 2900-3000km thick
• made up of molten and semi molten rocks containing lighter elements such as silicon and oxygen
• Subdivided into the: upper mantle and lower mantle
• Upper mantle: roughly about 700km down, solid - cool enough - hasn’t reached melting point, pressure low enough to still be somewhat fluid
• Lower mantle: higher pressure - less fluid, thicker

Question 6

Describe features of the crust

Answer 6

• 30-60km deep
• Continental crust and oceanic crust
• Solid
• Divided into tectonic plates (solid rock)

Question 7

Describe what the lithosphere is

Answer 7

• Consists of the crust and the rigid upper section of the mantle and is approximately 80-90km thick
• Divided into seven very large plates and a number of smaller ones
• Plates divided into oceanic or continental depending on the type of material they are made from

Question 8

Describe features of continental crust

Answer 8

Thicker, older, lighter, mainly composed of granite, 35km thick on average - this increases under mountain chains, less dense than oceanic, formed primarily at subduction zones at destructive plate margin, the rocks contain mainly silica and aluminium and granites are the most common.

Question 9

Describe features of oceanic crust

Answer 9

Younger, heavier, mainly composed of basalt - containing silica and magnesium, mainly formed at constructive margins or spreading mid ocean ridges, 6-10km thick, constantly destroyed and recreated because of the processes taking place along ocean ridges and destructive plate margins

Question 10

Describe the athenosphere

Answer 10

Lies beneath the lithosphere and is semi-molten on which the plates float and move