Lecture Two

Question 1

What is a scientific theory?

Answer 1

Scientific theory consists of one or more hypotheses based on observations.
Observations –> Hypothesis –> Theory (repeat)

Question 2

How do we know the basic structure of the Earth?

Answer 2

• By observing the vibrations caused by earth quakes, that is, their reflection, absorption and refraction.
• By looking at the magnetic and physical properties of rocks and minerals and their behaviours under extreme temperature and pressure in a lab (replicating the conditions thought to exist in the layers of the Earth).
• By looking at the distribution of rocks and fossils around the world.
• By looking at satellites, which can monitor the movement of tectonic plates and the continents.

Question 3

What are the Earth’s layers, and what are their characteristics?

Answer 3

1) Atmosphere

2) Continental crust
- 25 - 70km thick
- Less dense than oceanic crust

3) Oceanic crust
- ~7km thick
- More dense than the continental crust

4) Upper mantle
- Solid

5) Lower mantle
- Solid, but over time acts ‘fluid’ due to convection currents

6) Outer core
- Predominantly iron and nickel
- Solid due to extreme pressure, despite extremely high temperatures

7) Inner core
- Predominantly iron
- Mostly solid, despite extreme temperatures, due to extreme pressure

Question 4

What and where are the asthenosphere and the lithosphere?

Answer 4

The lithosphere includes the crust and the upper mantle.

The asthenosphere is directly underneath the lithosphere. The asthenosphere is responsible for volcanoes.

Question 5

What is a divergent boundary?

Answer 5

A divergent boundary occurs when two plates are moving away from one anther and new crust is forming from magma that rises to the surface between the plates from the mantle.
Also known as mid ocean ridges, ridges and spreading boundaries.

Question 6

What is a convergent boundary?

Answer 6

A convergen boundary occurs when to plates are moving towards each other.
If the two plates are of equal density, they usually push up against each other and form mountains.
If they are of differing densities, one will sink beneath the other in a subduction zone.
Also known as subduction zones, convergent margin, consuming boundary or trench.

Question 7

Define subduction.

Answer 7

When the oceanic crust becomes a part of the mantle.