# Is geothermal energy ultimately derived from solar energy?

The following question is taken from 10th class science NCERT book chapter 14th.

Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy? (a) geothermal energy (b) wind energy (c) nuclear energy (d) bio-mass.

The answer is given as (c) nuclear energy.

I understand that the wind moves because of the uneven heating of the earth by the sun. And biomass uses solar energy for photosynthesis.

How is geothermal energy ultimately derived from the sun?

• I've removed a number of comments that were attempting to answer the question and/or responses to them. Please keep in mind that comments should be used for suggesting improvements and requesting clarification on the question, not for answering. – David Z Jul 7 '20 at 20:43

It is not a correct statement:

Geothermal energy comes from the heat within the earth. The word "geothermal" comes from the Greek words geo, meaning earth," and therme, meaning "heat." People around the world use geothermal energy to produce electricity, to heat buildings and greenhouses, and for other purposes.

The earth's core lies almost 4,000 miles beneath the earth's surface. The double-layered core is made up of very hot molten iron surrounding a solid iron center. Estimates of the temperature of the core range from 5,000 to 11,000 degrees Fahrenheit (F). Heat is continuously produced within the earth by the slow decay of radioactive particles that is natural in all rock

italics mine.

Geothermal energy comes from the original energy of the matter solidifying into the sun-planetary system, ultimately from the Big Bang, and from continuous nuclear decays and reactions .

• Do you have a source to dispute wikipedia: "An estimated 45 to 90 percent of the heat escaping from the Earth originates from radioactive decay of elements mainly located in the mantle", or are you saying something different? – Jason Goemaat Jul 6 '20 at 14:41
• Could part of geothermal come from gravitation (tidal effects)? – kjetil b halvorsen Jul 6 '20 at 16:37
• @kjetilbhalvorsen Yes, but tidal effects ultimately takes energy from Earth's rotation. – lvella Jul 6 '20 at 17:29
• @JasonGoemaat Then better use the @ sign followed by the name of the person you are reacting to. Just like I did right now with you. SO even helpfully displays the names of the relevant people ready for you to click once you start typing the start of the name. That way, the person gets notified of your comment, and we see that you were addressing the comment, not the answer. – cmaster - reinstate monica Jul 6 '20 at 20:51
• @PM2Ring - I suspect you are thinking of radioactive heating in the core, which is hypothesized to be very small, instead of radioactive heating in the Earth as a whole, which is suspected to be somewhere between a highly significant to the dominant source of heat escaping from the Earth's interior. – David Hammen Jul 6 '20 at 22:55

No , the geothermal Energy is not derived from Sun's Energy or Has any relation to Sun's heat energy under normal circumstances. It comes/transforms/translates from within the Earth's Crust through several Chemical and Physical Events inside.

The Answer given is Nuclear Energy , because Of the RadioActive Decay of Matter inside the crust but this is one of the factors that may result in Thermal Energy

An excerpt from Wikipedia says this.

Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. The geothermal energy of the Earth's crust originates from the original formation of the planet and from radioactive decay of materials (in currently uncertain but possibly roughly equal proportions).

Wikipedia Article Here About Geothermal Energy

• Well. It comes from a Sun's energy. Just not our current one. – Steve Cox Jul 6 '20 at 20:57
• @SteveCox I think there is only one star named the Sun, and a different start could be called a sun. – Volker Siegel Jul 6 '20 at 21:36
• @SteveCox Can you elaborate ? , I didn't follow – german_wings Jul 7 '20 at 2:27
• Don't bother with SteveCox's comment, it's just juggling with words. He's alluding to the fact that the heavy nuclei in our system seem to have come out of some long-forgotten supernova long ago. Which includes all the major sources of long-term radioactivity. But that's just derailing the discussion, for when we talk about "solar energy" we really mean the one star that our planet orbits. – cmaster - reinstate monica Jul 7 '20 at 13:43

To the extent that Geothermal Energy arises from the Primordial Energy from the accretion of the planets during the formation of the Solar System, you could correctly argue that Geothermal Energy is also ultimately attributable to the sun, albeit via the suns gravitational attraction rather than it's radiation. More precisely, however, Geothermal energy is comes not only this 'Primordial Heat, but also from 'Radiogenic Heat' from the decay of radioactive isotopes, in roughly similar proportions. According to this Wikipedia article the ranges of these sources are estimated at 15–41 TW and 12–30 TW for radiogenic heat and primordial heat, respectively. https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget

• Accretion wasn't due to the sun's gravity. – Acccumulation Jul 7 '20 at 19:58

Geothermal energy, ultimately, is derived from the Sun. How can that be? There's a couple of ways you could look at it.

First, models for planetary formation involve material ejected from primordial supernovae slowly coalescing under the force of gravity. Nearly all matter and energy trapped in the core of the Earth originated inside the Sun (not the same Sun, technically, since the current Sun formed out of that same supernova explosion the Earth came from).

Secondly, thermal energy is only useful when there is a temperature gradient. At the end of a thermal reaction (uniform temperature), the amount of energy in a system is the same, but no more meaningful work can be done with it. So the thermal energy in the Earth's core is only useful to us because of the relatively cooler surface temperature, and the surface temperature of a planet is directly attributable to the amount of solar energy it receives (among other things).

You could even argue that solar energy is nothing more than a side-effect of nuclear energy, the direct result of thermal energy released by nuclear fusion of lighter elements into heavier elements. But you can't argue that nuclear energy is the result of solar energy. It's kinda like how all squares are rectangles, but not all rectangles are squares.

• I think it's a main point whether it's from the star in the center of the Earth orbit, called the Sun, or any other star, be it sun-like or not, which you might call a sun. – Volker Siegel Jul 6 '20 at 21:33
• There is only one Sun (note the capitalization) in the entire universe. – David Hammen Jul 6 '20 at 23:01
• The matter that formed the Solar System didn't just come from a single supernova, it came from millions of stars. Please see How can there be 1,000 stellar ancestors before our Sun? OTOH, a supernova may have triggered collapse in a molecular cloud, leading to the formation of the Solar System, and probably several other star systems. – PM 2Ring Jul 7 '20 at 0:41