Re: How much heat from the earth's core contributes to our conditions?

We are told that the sun is the source of life on earth, and it clearly makes a large contribution. However, the earth's core also appears to contribute. How much of a contribution does it make? Relative to the sun?

Also, does the heat from the earth's core "drive" ocean currents to any significant degree? If not, what is the source of this energy?

Obviously the number is higher at the equator and lower at the poles; the number is also averaged over the whole surface, while only half of the Earth receives sunlight at any given time. The energy intercepted by the Earth may be calculated by determining the surface area of the sphere of 1 AU radius, dividing into the cross-sectional area of the Earth, and multiplying by the Sun's total output. The Earth's radius is 6378 km.

Given the closeness of the numbers (±32 watts < 10%), the Earth radiates little or no more energy than it receives from the Sun. In other words, there is no significant energy received at the Earth's surface from any interior source. (Contrast this with Jupiter, which radiates about 10 times the energy it receives from the Sun.)

This answers your second question: the energy which drives ocean currents comes from the Sun, not from the Earth's interior. One has to go more than 100 miles down (the boundary between the Earth's crust and upper mantle) before reaching a point where interior heat is the primary driving force for physical processes.

Resources used in preparing this answer:

• Sooby Bhattacharjee's Blackbody emission calculator (with wavelength limits of 0.4 angstrom to 50 km, "Total emissive power" is the pertinent readout.)
• The Nine Planets

> quotes of my initial answer

I think you need to take the total amount of energy into account here. See below for a detailed exposition.

Firstly, what is a blackbody? I gather this relates to heat generation, or lack thereof?

A blackbody is an object which perfectly absorbs all radiation which falls on it. When heated to incandescence, it radiates all frequencies, with lambda-max dependent on temperature. (Read any history of quantum mechanics for "the ultraviolet catastrophe" which involved blackbody radiation and was solved by Planck's introduction of the quantization of energy.)

> Given the closeness of the numbers (±32 watts < 10%), the
> Earth radiates little or no more energy than it receives from the
> Sun. In other words, there is no significant energy received at the
> Earth's surface from any interior source. (Contrast this with
> Jupiter, which radiates about 10 times the energy it receives from
> the Sun.)

> This answers your second question: the energy which drives ocean
> currents comes from the Sun, not from the Earth's interior. One
> has to go more than 100 miles down (the boundary between the
> Earth's crust and upper mantle) before reaching a point where
> interior heat is the primary driving force for physical processes.

Is it then true to say that ocean currents are driven by the sun's energy input only? Is there any other contributor, such as the kinetic energy of the earth's rotation, or the presence of the moon?

For exact contributions you need an oceanographer, not a chemist or a physicist. But I can say the following:

1. Most (if not all) the heat from the Earth's interior is converted into the mechanical energy of plate motion. Convection cells within the mantle are thought to drive crustal plates across the earth's surface. Some heat is dissipated by volcanic activity; the waste heat from friction associated with plate motion goes partly into earthquakes; my guess is that very, very little is actually radiated to the oceans as "general heat" over a wide area (as opposed to local heat contributions from an underwater volcano).

2. Remember that factor of 10%. Even if all the excess heat at the Earth's surface (and its 10% overage of expected blackbody radiation from what it receives from the sun) is due to internal heat, it still means that 90% of the earth's surface heat is received from solar radiation. Thus, it is quite doubtful that internal heat has any major effect on the overall system of ocean currents. Coriolis forces probably contribute somewhat; currents tend to move, like the trade winds, in one direction in the Northern Hemisphere and the other in the Southern Hemisphere; but again I'd bet most of the actual driving energy comes from the sun.

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2/21/2000
Thank you to Mike Fox, who pointed out that radioactivity is the primary source of the roughly 10% excess heat that the Earth radiates, and further that radioactivity provides the heat which drives geophysical processes such as plate tectonics, the Earth's internal dynamo, and other effects of convection within the Earth.
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