The structure of the Earth - plate tectonics

Question 1

How did the Earth supposedly start?

Answer 1

Estimated to be 4.6 billion years old - Big Bang.
Ball of molten materials - slowly cooled to form a crust of solidified rocks.
Gasses escaping from Earth’s interior via volcanic activity - formed a primitive atmosphere.
Many asteroid impacts.
Not conducive to life.
No oceans, flowering plants etc.

Question 2

What is some old Earth evidence?

Answer 2

Oldest rocks on planet Earth - 2.5-3.8 billion years.

Oldest - found in Canadian Shield - coastline of Hudson Bay.

Question 3

What are the ‘newest’ main Earth features?

Answer 3

Rocks in North West Iceland - 16 million years old.
Some older underlying volcanic rocks - 37 million years old.
British Isles - half as old as the planet.
Humans are very new - arriving only 2.3-2.4 million years ago in Africa.

Question 4

How are plates supposedly formed?

Answer 4

Lithosphere - cooling of molten materials - forms crust.
Rocks fractured into huge segments - tectonic plates.
Slowly pushed around by convection currents.

Question 5

What is the Earth’s structure?

Answer 5

Lithosphere - hardened crust - O2, aluminium (light).
Asthenosphere - semi-molten.
Plates float and move on this - convection currents.
Mantle - molten/semi-molten rocks - oxygen and silicon.
Core of Iron/Nickel (solid) - temperature of 6200°C - intense pressure there.

Question 6

What are P waves?

Answer 6

(Primary).
Fastest waves.
Travels through liquids and solids.
Vibrate in the wave travelling direction.

Question 7

What are S waves?

Answer 7

(Secondary)
Slower than P waves - travel at roughly half their speed.
Shake the ground from side to side by vibrating at right angles to the direction of travel.
Solids only.

Question 8

What are L waves?

Answer 8

L - surface only.
Slowest waves.
Two types:
Love waves - vibrate at right angles to the direction of movement but have no vertical movement.
Rayleigh waves - have both vertical and horizontal displacement of the ground.

Question 9

Why are P,S and L waves important?

Answer 9

P/S - travel through Earth’s interior - be recorded on seismographs.
P/S travel at different rates - depends on material.
S - solids only - molten mantle has been detected.