Earth Structure: Indirect and Direct evidence

Question 1

Name the planets in order?

Answer 1

Mercury
Venus
Earth
Mars
(Asteroid Belt)
Jupiter
Saturn
Uranus
Neptune

Question 2

What is the asteroid belt?

Answer 2

Fragments of a terrestrial planet that either failed to form, or formed and broke up

Question 3

What is a comet

Answer 3

Composed of ice and dust which melts as it passes the sun creating a trail.

Question 4

What is the difference between a meteor and a meteorite?

Answer 4

Meteor - Burn up in the atmosphere
Meteorite - Rock fragments which fall and load on the Earth

Question 5

Define bolide

Answer 5

The term for an impacting extraterrestrial object

Question 6

Define ejecta

Answer 6

Material that fly’s out of the crater when a bolide hits the ground. It lands on the rim on top of the old rock called inverted strata

Question 7

Define brecciated

Answer 7

Broken rock

Question 8

What is usually found in an impact crater?

Answer 8

Radial pattern of ejecta
“Shocked” quartz grains
Tilted strata
Iridium

Question 9

How old is:
The Earth
Meteorites found in the solar system
And the solar systems age

Answer 9

All roughly 4.567 Ga (Billion years old)

Question 10

What are three types of meteorites?

Answer 10

1. Stony (93% of meteorites) = Represent mantle rocks (Silicates)
2. Iron (6% of meteorites) = Represents our core
3. Carbonaceous Chondrites (1% of meteorites) = Represents the Earths water + organic compounds

Question 11

How old is the universe?

Answer 11

13.7 - 14.0 Ga (Billion years old)

Question 12

What is the Nebular disc theory?

Answer 12

Gas and dust shockwave from an old supernova. This causes the nebular to collapse and spin. Nuclear fusion starts and a star is born. The heavy elements accumulate making planetesimals.

Question 13

What is elastic rebound theory?

Answer 13

Undeformed crust deforms due to stress. Faults in the crust occur when the crust folds and snaps and the crust reforms to its original state.

Question 14

Define focus and epicentre

Answer 14

Focus - Origin of the Earthquake
Epicentre - Point on the surface nearest to the focus

Question 15

What is a seismometer and seismograph?

Answer 15

Seismometer - Machines used to measure earthquakes that use inertia
Seismograph - The result of the measured earthquake

Question 16

What is a P-Wave

Answer 16

Are compressional waves and arrive first. Have the highest velocity (and travel through any material but are slower when travelling through liquids and gases)

Question 17

What is an S-Wave

Answer 17

Arrive second and can only pass through solids. Secondary shear/shake waves. Stopped by liquids and gases.

Question 18

What is an L-Wave

Answer 18

Two types: Rayleigh waves have a vertical motion and love waves have a horizontal motion. Longitudinal waves that arrive last as they are slowest. They are confined to the surface and dissipate rapidly but do the most damage.

Question 19

What does rheid mean?

Answer 19

A solid material that acts as a liquid

Question 20

At what angle is the P-Wave shadow zone?

Answer 20

103-142 degrees

Question 21

At what discontinuity are P-Waves refracted?

Answer 21

Gutenberg

Question 22

At what discontinuity are S-Waves stopped at?

Answer 22

Gutenberg

Question 23

At what angle is the S-Wave shadow zone?

Answer 23

103 degrees both sides

Question 24

What are the three discontinuities?

Answer 24

Moho - Crust 35km
Gutenburg - Separates lower mantle and outer core at 2900km
Lehmann - Separates outer core from inner core 5100km

Question 25

What is the lithosphere and how thick is it?

Answer 25

Contains the crust and the upper mantle 100km thick

Question 26

What is the asthenosphere and how thick is it?

Answer 26

The low-velocity zone (Lower mantle) where most material is a rheid and body waves slow down 100-2900km

Question 27

How thick is the outer core and what is it made of?

Answer 27

2900km - 5100km Made of molten liquid

Question 28

What is the inner core made of?

Answer 28

Solid, iron/nickel

Question 29

What are 4 bits direct evidence for the Earths composition?

Answer 29

-Deepest gold mine (4km) In South Africa
-Deepest borehole (12km) In Siberia
-Volcanos- xenoliths from the mantle found in kimberlite pipes which can tell us the chemistry, temperature and pressure.
-Ophiolite suites - Failed subduction thrusting oceanic crust upwards and we can study it to find the crusts composition.

Question 30

What does oceanic crust consist of?

Answer 30

Top
Sediments
Basalt pillow lavas
Dolerite Dykes
Gabbro
Peridotite
Bottom

Question 31

What are 4 bits of indirect evidences for the Earths composition?

Answer 31

-Missing mass- Most surface rocks have a density of 2.7g/cm^3 but the earth is 5.5 g/cm^3
-Iron has the right density and is common to explain the cores material and magnetic field
-Body waves
-Gravitational anomalies: positive shows denser rocks, negative shows less dense rocks
-Meteorites

Question 32

How did mohorovicic discover the moho discontinuity

Answer 32

Some S and P waves were arriving at faster speeds than expected. He found that they were taking a faster but longer route through the rigid upper mantle.

Question 33

What does Goldschmidt’s classification contain?

Answer 33

is a geochemical classification which groups the chemical elements according to their preferred host phases
1. Lithophiles (Rock loving elements) - Crust
2. Siderophiles (Iron loving elements)- Core
3. Chalcophiles (Ore loving elements) - Mantle
3. Atmophiles - Atmosphere + hydrosphere

Question 34

What happens to body waves when they travel through hotter rocks?

Answer 34

They slow down

Question 35

What causes the northern lights?

Answer 35

The magnetosphere allows charged particles to collide with atoms in the atmosphere which produce photons

Question 36

What is the self-exciting dynamo effect?

Answer 36

The liquid outer core flows around the solid inner core, generating electricity, inducing magnetism, which generates more electricity and therefore more magnetism. Repeats.

Question 37

How can we see where the poles were in the past?

Answer 37

Iron-rich minerals in igneous materials line up like compass needles. When the rocks pass the curie point, the minerals freeze in position lined up in the direction of the magnetic poles at the time. Called remnant magnetism.

Question 38

What is the angle of inclination?

Answer 38

Used to find the latitudes of volcanos at the time that it erupted. Shows the angle that they make with the horizontal ground. The dip is the same as the latitudes.

Question 39

What is the geothermal gradient?

Answer 39

Is the change in temperatures with increasing depth towards the centre of the Earth.