Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: TommySpitz on 12/02/2020 07:58:02
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Hi, I'm asking this because of an ongoing discussion on the subject which is causing its own heat. Here's the subject: as per the title question, I propose that heat radiating from the Sun over the last 4.5 billion years continues to move through the body of the Earth towards its centre, and clearly, under this proposition has already reached the core long ago and continues to do so, albeit probably in minute quantities. This is refuted, the opposition claiming that the heat from the Sun stops at the crust. I say this is scientifically unlikely. So my point is - if heat stops at the crust as they claim, at which depth does it stop, and why? They can't answer.
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The first thing to say is that, due to thermodynamics, heat naturally moves away from a hot temperature and toward a colder temperature*.
The surface temperature of the Sun is around 5500C.
- The temperature of deep space is about -270C, so heat moves outward from the Sun towards deep space.
- The Earth and Moon are partway between the Sun and deep space.
- The Moon has an average surface temperature of about -15C, although it has extreme temperature swings between its 2-week long daytime and its 2-week long night-time.
- The Earth, due to its blanket of warming air, has an average temperature around +15C. Due to the oceans, and our relatively quick rotation, the temperature swings are far more tolerable in temperate climates.
The core temperature of the Earth is about 6000C.
- That means that heat will flow out from the core of the Earth towards the cooler surface.
- But since the core is surrounded by a thick blanket of rock, the rate of heat escape is about 0.08 Watts/m2, averaged over the whole Earth
- This produces a temperature increase near the surface of around 15C per km of depth (although it's more in geothermally active areas).
So we have the surface of the Earth, irradiated by about 700 Watts/m2 in direct sunlight, increasing perhaps 10C during the day and cooling during the night.
- The thermal inertia of rocks means that this daily variation of temperature won't penetrate very far into the ground, although annual temperature variations due to the seasons might be detectable 1m underground.
So I would suggest that heat flows from the Sun perhaps 1m into rock during summer (and out again in winter).
It definitely would not penetrate more than 1km into the crust, because the temperature there is significantly above summer temperatures at the surface - and heat naturally flows from hot temperatures to colder temperatures.
So I vote with the opposition - heat from the Sun stops at most 1km below the surface of Earth's crust.
*Excluding things like refrigerators, which expend energy to move heat from a cool temperature to a warmer temperature.
See: https://en.wikipedia.org/wiki/Geothermal_gradient
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The first thing to say is that, due to thermodynamics, heat naturally moves away from a hot temperature and toward a colder temperature*.
The surface temperature of the Sun is around 5500C.
The core temperature of the Earth is about 6000C.
Which also means that if it were not for the intervening rocks radiating heat at night, the earth would in fact be heating the sun by radiative transfer! Counterintuitive or what?
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Can I take it then, that over billions of years and disregarding the Earth's mass that the ambient temperature of the planet Earth is unaffected by the Sun?
I understand crust warming - that's basic stuff, but your implication is that there's either a physical point when the heat from the Sun stops penetrating the Earth, or there's a point when the atomic structure of the Earth (or any heated object) ceases to react to the incoming heat - which must be a calculable known. Guessing at about 1metre does not highlight the mechanics, so to speak.
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Can I take it then, that over billions of years and disregarding the Earth's mass that the ambient temperature of the planet Earth is unaffected by the Sun?
I understand crust warming - that's basic stuff, but your implication is that there's either a physical point when the heat from the Sun stops penetrating the Earth, or there's a point when the atomic structure of the Earth (or any heated object) ceases to react to the incoming heat - which must be a calculable known. Guessing at about 1metre does not highlight the mechanics, so to speak.
Lots to unpack here:
First: the surface temperature of the Earth is very much determined by the sun (hence why it is typically colder at night than during the day, and colder during the winter than the summer), but overall, the Earth is not continuously just increasing in temperature due to heat from the sun, because the earth is also radiating (note that the atmosphere controls the rate of this radiation).
Second: I think it is important that we distinguish between "heat," "thermal energy," "temperature," and the "flow of heat." Also, there is some danger when ascribing whether "heat" "belongs to" or "came from" an object... Some of the energy from the sun comes to the Earth and warms the surface. Some of this energy continues to be transferred by convection, conduction and radiation, all the way to the center of the earth. However, most of the energy does not do this, and because the center of the earth is very hot (some residual heat from the formation and stratification of the earth, and some from radioactive decay) there is actually more energy leaving the center of the earth than coming in. By my reading, evan_au is saying that the heat from the sun is not penetrating below a certain depth because the net flow of thermal energy is out (again, this doesn't mean that no energy is going in, it just means more energy is coming out than going in--there is a depth at which those two are equal, and would be a calculable depth, based on some assumptions, and subject to change as the earth rotates and orbits etc.)
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Hi again, You said that "some of this energy continues to be transferred by convection, conduction and radiation, all the way to the center of the earth". Is it not just conduction?
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I would imagine that it is more than just conduction, especially since the mantle is fluid, so convection is a significant mechanism for heat transfer in the earth. Radiation is probably pretty small since conduction and convection both apply, but solid matter emits and absorbs photons at temperatures relevant to this discussion, so some of that energy will be transferred by photons.
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Thanks for that. The whole issue was raised by a great person I once met who said quite simply that 'nothing dies'. From the law of conservation of energy it then seemed likely that heat, or rather energy, from the Sun would eventually reach the core of the Earth. This was vehemently denied by those I mentioned. To my mind this is the denial of the most basic science, albeit complex to prove. There must be a mathematical standard somewhere to prove this.
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Your Great person was wrong. Everything dies. dS/dt > 0 is the universal law.
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Thanks for that. The whole issue was raised by a great person I once met who said quite simply that 'nothing dies'. From the law of conservation of energy it then seemed likely that heat, or rather energy, from the Sun would eventually reach the core of the Earth. This was vehemently denied by those I mentioned. To my mind this is the denial of the most basic science, albeit complex to prove. There must be a mathematical standard somewhere to prove this.
You're ignoring the fact that only one side of the Earth is receiving sunlight at a time and that the unlit side is radiating energy away into space. The energy conservation argument would only be valid if the Earth held on to all the energy it absorbs from the Sun, but it doesn't. The Earth radiates that energy fast enough that the surface never gets hot enough for that heat to penetrate very far into the surface. The interior of the Earth is so much warmer through radioactive decay and residual heat of formation that the any heat flow tends to got the other way.
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So at what point does heating stop? There must be a known. Or is it all guesswork?
I still maintain the energy (in whatever form) continues inwards.
"...energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another."
Law of Conservation of Energy.
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There must be a known. Or is it all guesswork?
There are many knowns - and they all produce different answers.
- If you know the thermal conductivity and heat capacity of a material, you can calculate it
- If you know the variable heating from one side, and the steady heating from the other side, you can calculate it.
- If it is solid rock, is it granite, limestone, or sandstone? is it wet or dry? (sandstone can hold a lot of water)
- Daily and seasonal heating depends on the latitude, altitude and cloud cover.
So solid, dry granite will show almost no seasonal variation 1m below the surface, at the equator.
However, a stream flowing through open air, and then into a limestone cavern 100m below the surface will show daily variations 100m below the surface.
And the depth of heating of the sea depends on how much winds ruffle the surface.
So you could calculate it, but you need to have more data than provided in the OP.
- And the results may be quite different for a different scenario
But the overall trend is the same - there is some equilibrium point where the Earth's internal temperature (of around 6000C) exceeds the daily and seasonal variations from Sunlight at Earth's surface (with an effective average temperature of around 15C).
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"Your Great person was wrong. Everything dies. dS/dt > 0 is the universal law." alancalverd
Universal law according to who? I'm afraid we're drifting here: how do you define time for a start?
Are you saying that 'energy' dies?. This flies in the face of the Law of Conservation of Energy, no?
My premise may disturb the givens of the scientific world, but it cannot be dismissed with man-made laws (which incidentally throughout time have been disproven).
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Can I take it then, that over billions of years and disregarding the Earth's mass that the ambient temperature of the planet Earth is unaffected by the Sun?
No
Obviously not, because you will have noticed that it gets cold at night.
Are you saying that 'energy' dies?.
Do you know what entropy is?
Alan's post say that entropy increases (for any isolated system yada yada...)
That's not the same as saying that anything happens to the energy.
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Are you saying that 'energy' dies?. This flies in the face of the Law of Conservation of Energy, no?
No one said energy dies. You were told that the sun's energy radiates back into space, so there is no violation of the conservation of energy.
My premise may disturb the givens of the scientific world, .
No one is disturbed, we are just trying to help with your question.
but it cannot be dismissed with man-made laws (which incidentally throughout time have been disproven).
If scientific principles disagree with your premise then science is wrong? Hmm, I'm starting to think you had a statement to make instead of a question to ask.
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Did you read the posts? I was responding to alancalverd's statement "everything dies".
I'm done here. Thanks everybody.
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I have split this thread, putting the unfounded theories posed by acsinuk (and responses thereto) into the "New Theories" section. The new topic can be found here: https://www.thenakedscientists.com/forum/index.php?topic=78859.0
In the future, please don't clutter up other discussion threads with your own pet theories, thank you!
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With all due respect, your attitude and views are bogged down in the 'what is' - dead knowledge passed down through the ages. True science is the consideration of the unlikely, the seemingly unapparent; in this way discovery is made, not by quoting archaic formulae. My initial enquiry remains valid.
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The inquiry is quite valid, and the discussion is interesting.
However, the notion that the sun is made of antimatter is experimentally falsified. acsinuk has a few closely-intertwined pet theories that are definitely wrong, and has been warned multiple times in the past not to insert them into other discussions. (Imagine if a young earth creationist had tried to answer your question by claiming that in fact the earth wasn't billions of years old, but only 6000ish years, and then continued to insist on it, disrupting any discussion of the original question)
TommySpitzt, I would also urge you to be less ready to dismiss "knowledge passed down through the ages" as dead, especially when it comes to "archaic formulae." These mathematical expressions are constantly checked and rechecked against experimental tests, and have held up against ages of testing and revalidation.
While it is true that some don't question the fundamentals as much as they should, and that there may indeed be some underlying assumptions that are incorrect and holding us back, I would suggest that we wait until the old models fail us before looking for errors in them. (How many man-hours must be devoted to re-discovering the periodic table, or re-deriving the relationship between electricity and magnetism?)