Lecture 6

Question 1

What caused the size increase of the proto-earth?

Answer 1

Accretion of particles of molten matter-atmosphere was cold, surface formed a crust of solid material.

Question 2

What caused an increase in temperature of the proto-earth?

Answer 2

Collisions from asteroids, debris, protoplanets etc, and the decay of radio active elements trying to find stable state. Heat was trapped inside the core and turned liquid.

Question 3

What is the gravitational differentiation process?

Answer 3

Different elements moved to different parts of the Earth due to the gravitational field-As Iron and Nickel reached their melting points, they moved towards the centre and silicate moved upwards.

Question 4

How did we first attempt to investigate Earths interior?

Answer 4

Wells (can’t go past 5000m). Miners (cant go past 2500 metres).

Question 5

What is seismic investigation?

Answer 5

Looks at the surfaces of discontinuity (boundaries of layers). Behaves differently at the seismic activity. Place Geophones at the surface and detonate-energy propagates through Earths interior. Measures waves that are reflected back by the surfaces of discontinuity.

Question 6

What are Earthquakes?

Answer 6

Natural phenomena generated by the rearrangement of Earth’s layers.

Question 7

What is the hypocentre?

Answer 7

Underneath the epicentre-distance between the two makes the earthquakes depth. Used to localize.

Question 8

What are body waves and the two types?

Answer 8

Waves which travel throughout the Earth. P-Waves: The first waves to get to the seismic observatories (very fast). S-Waves: Slower, produce damage.

Question 9

What are surface waves?

Answer 9

Last to reach seismic observatories. Extremely destructive.

Question 10

What is the chemical composition of the Earth?

Answer 10

Core (iron dominated, nickel 2nd). Mantle (silicates with low diversity. Crust (silicates with high diversity)

Question 11

What is the Guttenberg discontinuity (chemical)?

Answer 11

Boundary between the core and the mantle.

Question 12

What is the Mohorovich discontinuity (chemical)

Answer 12

Boundary between the mantle and the crust.

Question 13

What are the physical compositions of the Earth? (from outermost to innermost).

Answer 13

Lithosphere (solid), Athenosphere (exists solely on Earth, mobility of surface and existence of lifeforms, continents float on it, plastic surface), Mesosphere (solid, most of the volume of the earth (like the mantle), Outercore (Guttenburg discontinuity-only shared thing with chemical. Liquid Iron state due to temperature), Inner core (same chemical composition as outer, but is SOLID, due to very high pressures.

Question 14

How do we know the outer core is liquid?

Answer 14

S-waves can’t travel through it

Question 15

Where is the Moho discontinuity at a lower depth?

Answer 15

Continents

Question 16

What are the properties of the Oceanic Crust?

Answer 16

Thin, silicate dominated (Fe, and Mg) Denser than continental

Question 17

What are the properties of the continental crust?

Answer 17

Thick and silicate dominated BUT of lighter metals (Si, AL, Na, K). When a continent collides with oceanic crust, the oceanic crust moves under the continent.

Question 18

Which plate has been moving under the Americas?

Answer 18

Pacific Plate

Question 19

What did Francis Bacon discover about the shapes of continents?

Answer 19

There is a perfect match between the shores of South Africa and Europe.

Question 20

What did Alfred Wegener discover?

Answer 20

Igneous rocks in Africa and SA had similar chemical compositions, and also discovered rocks only found in glacial conditions in SA, Africa, Antarctica, and Australia. Observed a type of fern that reproduces through seeds rather than spores. Also found the Mesosaurus (skeletons in both SA and Africa, how did it swim there?)

Question 21

What was the interpretation of Alfred Wegeners data?

Answer 21

Supercontinent existed (Gondwana-from southern hemisphere).

Question 22

Which plates move with the Athenosphere?

Answer 22

Lithospheric.

Question 23

What are the 7 lithospheric plates?

Answer 23

North American Plate, Eurasian Plate, Australia Indian Plate, Pacific Plate, South American Plate, Antarctic PLate

Question 24

Which is the only Oceanic lithospheric plate?

Answer 24

Pacific.