How is heat transferred from the core through the mantle to the crust?

Question

So, there are three main methods of transferring heat: radiation, convection/mass transfer, and conduction. Presumably radiation is not a major method of heat transport between the core and the crust, because it requires transparent materials (or a vacuum), and I don't think there is much of either in the mantle. Presumably conduction is the only significant method of transport in the crust, apart from volcanos.

So, in the mantle, between the core, where heat is generated, and the crust, where it is eventually dissapated, what proportion of heat is transported via convection and conduction?

Answer 1

It is still a little known fact that radiation play an important role in the Earth's mantle. Experiments show that mantle-material becomes transparent to infrared radiation at increasing pressures (http://www.esrf.eu/news/general-old/general-2004/earthbadro/index_html).

I would also say that the mantle is currently not understood in a way where estimates of heat-conduction-type versus depth can be accurately made. The heterogeneity of heat transfer (Cold detached subduction-slabs sinking to various depths and hot plumes quickly rising from the D''-layer) makes the question even more difficult.

Answer 2

Conduction probably is the main method in the crust, but do not underestimate fluid convection.

Every time you find a hot spring, then that is an example of fluid convection. Even volcanic eruptions could be considered convection.

Possibly even larger than these too, there is vigorous convection of seawater through young ocean crust. This can be seen on Figure 10 of Muller eta al Digital Models of the World's Ocean Crust. This plots depth vs age of ocean curve. The "TBL" line approximates the curve that is expected for conductive cooling of the Earth's crust. Reality (the bars) are rather different. Although most of this cooling is in young rock, the accumulative effect shows in the older crust. (this plot is trying to demonstrate something else, but I couldn't find a good example of this classic graph that implied this convection must exist long before Black Smokers were ever discovered)

Answer 3

At wikipedia you can find some answers. http://en.wikipedia.org/wiki/Geothermal_gradient

Here it states that in the crust indeed conduction is the main method of heat trasfer. From the geothermal gradient it is also obvious that the outer core/mantle boundary is a big insulater. Since these two are separate heat transfer from the outer core to the mantle is also mainly by conduction.

For the mantle it is a story of both convection and conduction. I dont think the final answer is known here.

As an extra note. It seems that in your question you suggest that heat is generated in the core only. This is not true. Heat is also generated in the mantle through radioactive decay. This is estimated according to the linked wiki to be between 45 and 90% of the heat that escapes earth.