|MadSci Network: Earth Sciences|
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?
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?
S.A. = 4pr2 = 6.1´1018 m2
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.The average surface temperature of the Earth (which is another blackbody) is 287 Kelvins (14°C). This works out to an energy output of 385 watts per square meter, while we have calculated solar energy input as 353 watts per square meter (which corresponds to a surface temperature of about 281 Kelvins, or 8°C).
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:
> quotes of my initial answerFurther questions
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.)A point of clarification: the earth's surface temperature would be lower (about -14 C) if it were not for greenhouse gases in the atmosphere, which retain some of the energy radiated as heat, but eventually a new equilibrium is reached and the planet once more radiates most of what it receives from the sun. In point of fact, the temperature discrepancy makes up most of the difference between the (theoretical) blackbody radiation expected from the earth and 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.So what happens to this heat from 100 miles down? I find it difficult to accept that it just dissipates, particularly because there's even more energy just a bit deeper. And none of this energy is being radiated. Where does this energy go - it must DO something (work) to not be evident closer to the surface, surely? It can't just dissipate into nothingness!
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:
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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