Earth's Heat

Question 1

What are the two main contributions of surface heat on Earth?

Answer 1

• Solar heating (averages ~350Wm^-2)

- Heat flow from interior (averages ~150Wm^-2)

Question 2

What is the heat flow within the Earth dominated by?

Answer 2

The temperature gradient from the core to the surface.

Question 3

How was the formation of the Earth a source of heat?

Answer 3

Impact KE of planetesimals, iron catastrophe released GPE -> very large reservoir of heat

Question 4

How does radioactive decay release heat?

Answer 4

Each decay process releases large amount of energy over geological timescales

Question 5

How can we use radioactive decay to look at the heat of the Earth?

Answer 5

• Can detect ‘geoneutrinos’
• Estimate concentration of radioactive elements in to interior so can estimate internal heating
• Refine estimates of core temp

Question 6

What is the conductivity of the mantle material?

Answer 6

Thermal conductivity ~ 3-5 Wm^-1 K^-1

Question 7

What happens to do with convection within the Earth?

Answer 7

Strictly ‘advection’ i.e. motion of hot material masses (no diffusion)

Question 8

What is a geotherm?

Answer 8

A plot of the Earth’s temperature as a function of depth - can show liquid solid boundaries.

Question 9

What are the 3 possibilites for 2 parts of the mantle M1 and M2, one at P1 and T1, and the other at P2 and T2?

Answer 9

1- M2 cools to T1 = adiabatic
2- M2 cools to above T1 = superadiabatic
3- M2 cools to below T1 = subadiabatic

Question 10

What happens when M2 cools to above T1?

Answer 10

It will continue to rise and expand. M2 becomes less dense than surrounding material so rises.

Question 11

What does this model of M1 and M2 show for advection in the mantle?

Answer 11

That it creates a convection cell (material in constant circle moving around)

Question 12

How does the viscosity of the mantle compare to the viscosity of the outer core? What does this mean?

Answer 12

μ(mantle)&raquo_space; μ(core)

This means that thermal equilibrium is more easily obtained in the core.

Question 13

What are some important observations of the outer core having lateral temperature?

Answer 13

• Must be very non uniform heat transport to surface of earth and into mantle
• Must have non uniform structures of heat flow inside mantle

Question 14

What does seismology of the mantle-core boundary show us?

Answer 14

Seismic wave travel-time residuals show strong variations - “rough” hilly/valley layer around outer core.

Question 15

What is the D layer and what are some facts about it?

Answer 15

• Layer around outer core
• 200km thick
• Precise composition unknown
• Could be iron silicate, subducted cooler plate material or new post perovstsite materials
• Likely cause of uneven heat flow from core to mantle