Characteristic and Internal Structure of the Earth

Question 1

What shape is the Earth and why is this?

Answer 1

The Earth is an ‘oblate spheroid’. The bulge occurs due to the rotation of the Earth, as the Earth s slightly plastic (deformable).

Question 2

What is the approximate radius of the Earth?

Answer 2

6378km

Question 3

About how much does the Earth radius vary due to mountains and oceans?

Answer 3

+/- 20km

Question 4

What is an equation to approximate the actual radius of the Earth considering the bulge in terms of the latitude?

Answer 4

R(λ) = Req(1-f*sin^2(λ))

where f is the flattening

Question 5

What is the equation for f, the flattening of the Earth?

Answer 5

f = (Req - Rpol)/Req

Question 6

What is the approximate radius from pole to pole of the Earth?

Answer 6

Around 22km less than at the equator.

Question 7

What is latitude? What is its symbol?

Answer 7

Specifies the north-south position of a point on the surface. Runs from 90°N - 90°S, where 0° is the equator. Symbol can either be λ or ϕ

Question 8

What is longitude? What is its symbol?

Answer 8

Specifies the east-west position of a point on the surface. Relative to defined meridian at Greenwich. Goes from 180°W to 180°E. Symbol can either be λ or ϕ

Question 9

What is Δ in Geophysics?

Answer 9

Angular distance in radians.

Question 10

What is the equation for actual distance in terms of angular distance?

Answer 10

X = Req * Δ

where Δ is the angular distance.

Question 11

What is the Cavendish experiment and what was found?

Answer 11

Torsion balance used to measure gravitational attraction between two large masses and compare this to their weight using Newton’s law.

Question 12

What is Newton’s law of universal gravitation?

Answer 12

F = GMm/r^2

Question 13

Who drilled the deepest into the Earth and how far did they go?

Answer 13

Drilled to 12,262 metres before the temperature forced them to stop from 1970-1989.

Question 14

What is the equation for gravitational acceleration including Req?

Answer 14

geq = GMe/Req

Question 15

What is the integral equation for the moment of inertia?

Answer 15

I = integral over V of r^2 dm

Question 16

What is the moment inertia of the Earth (including Me and Re?

Answer 16

I = 0.331MeRe^2

Question 17

What are the 4 most abundant elements?

Answer 17

Oxygen, Magnesium, Silicon and Iron

Question 18

What does mass segregation mean?

Answer 18

Heavier elements are more abundant near the Earths centre.

Question 19

What are the layers of the Earth in order?

Answer 19

Crust, Mantle, Outer Core, Inner Core (mostly Fe).

Question 20

What is the average thickness of the Earth’s crust (continental and oceanic)?

Answer 20

35km (continental) and 7km (oceanic)

Question 21

What is the Mantle subdivided into? What happens at each subdivision?

Answer 21

Upper mantle (Olivine composition), 2 transition zones(1- high pressures cause olivine to undergo phase transition that releases heat. 2- spinek to perovskite with 10% increased density), lower mantle (core-mantle boundary).

Question 22

What are the mechanical divisions of the Earth? How does this differ to the other layers?

Answer 22

Lithosphere, Asthenosphere, Mesosphere, Outer Core and Inner Core. This is the heat transport of materials rather than the composition and crystal structure of the Earth.

Question 23

What does the Lithosphere include?

Answer 23

Includes crust and some of mantle - heat transport predominantly by conduction. Over geological time periods undergos brittle fracture and elastic deformation but is rigid on seismic wave timescale.

Question 24

What does the Asthenosphere include?

Answer 24

Rigid on short timescales, and hence behaves as an elastic solid, transmitting shear and compressional elastic waves. Over geological time, sufficiently hot that viscous flow can occur, and heat transport by convection.

Question 25

What does the Mesosphere include?

Answer 25

Becomes less ductile and more rigid with increasing pressure and temperature.

Question 26

What does the outer core include?

Answer 26

Low-viscosity liquid, so shear waves are not transmitted, but compressional elastic waves are transmitted. Drives the geodynamo which produces Earth’s B-field.

Question 27

What does the inner core include?

Answer 27

Solid region due to pressure-freezing, detected by reflection of seismic waves. May rotate slightly faster than rest of the Earth as it is not connected mechanically to the mantle.

Question 28

What does seismic activity show evidence for?

Answer 28

Compressional and shear waves - indicate solid core and liquid outer core, and sharp transitions in density.

Question 29

What is the composition of the Mantle rock?

Answer 29

Xenoliths - mantle rock brought to surface

Ophiolite - oceanic crust and underlying mantle brought to continent

Question 30

What is the composition of meteorites?

Answer 30

Largely olivine (Mg, Fe, Si, …) with some metallic iron

Question 31

What are 4 ways we can measure the age of rocks?

Answer 31

• Radiometric dating
• Palaeontology
• Stratigraphy
• Magnetic reversals