# Earth's Heat Flashcards

1
Q

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

A
• Solar heating (averages ~350Wm^-2)

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

2
Q

What is the heat flow within the Earth dominated by?

A

The temperature gradient from the core to the surface.

3
Q

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

A

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

4
Q

How does radioactive decay release heat?

A

Each decay process releases large amount of energy over geological timescales

5
Q

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

A
• Can detect ‘geoneutrinos’
• Estimate concentration of radioactive elements in to interior so can estimate internal heating
• Refine estimates of core temp
6
Q

What is the conductivity of the mantle material?

A

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

7
Q

What happens to do with convection within the Earth?

A

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

8
Q

What is a geotherm?

A

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

9
Q

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?

A

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

10
Q

What happens when M2 cools to above T1?

A

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

11
Q

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

A

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

12
Q

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

A

μ(mantle)&raquo_space; μ(core)

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

13
Q

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

A
• Must be very non uniform heat transport to surface of earth and into mantle
• Must have non uniform structures of heat flow inside mantle
14
Q

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

A

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

15
Q

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

A
• 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