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Earth, The Scofflaw Planet (Posted on 2018-07-09) Difficulty: 2 of 5
The second Law of Thermodynamics is pretty clear about it: The entropy of a system not in equilibrium will tend to increase over time. (Entropy may be thought of as disorder or randomness). But, consider the history of Earth: It is a system that started out as a semi-molten mess. Later, it cooled and developed life, and it made those pesky structured organisms that went on to populate the seas and produce our jungles and forests. Then came those advanced animals that fashioned everything, even cities. Cities are much more ordered than jungles and so their entropy is lower.
Entropy(cities) < Entropy(jungles) < Entropy(molten mess). So, what's going on? How did we manage to violate the law? Are we somehow miraculously, divinely above the rules?

  Submitted by Steven Lord    
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Solution: (Hide)
The 2rd Law explicitly only applies to "closed" systems, (I left the word "closed" out of the puzzle on purpose) which the Earth alone is decidedly not. And yes, folks caught that, but that is not all. One cannot simply include the "Sun-Earth" system to wriggle free of the violation, since the Sun itself would also be in violation, as it busies itself full-time making the more ordered Helium (and the occasional organic stuff) from simple Hydrogen .

To contemplate the closed Earth system, one must imagine a bubble at least 4.5 billion light years in radius that includes all the Sun's disordered light made from masses of hydrogen, and all of the Earth disordered infrared light shone outward over all the eons. The high order (lowered entropy) we have achieved on Earth is more than offset by our huge random IR light footprint into this spatial bubble. Far outside the solar system is where the increase of entropy of our closed system lies. Our heat-radiation, when included, has our total entropy ever increasing and leaves us in obedience of the 2nd Law of Thermodynamics.

Your honor, Dr. Clausius, I rest my case.

If you want to get into it a little deeper, please consider separately: the Sun; the Earth interior; and the Earth surface.

The Sun, in addition to providing the gravity that holds the solar system together, does mostly two other things: converts H to He via fusion, and each second turns an additional 4 million tons of H into energy. Each new He has less entropy than the four contributing H's, so the Sun loses entropy. However, the entropy of the fusion byproducts: radiation (gamma rays which eventually redistribute to visible light), positrons, and neutrinos, leave the total entropy of the system increasing. The light and neutrinos fill an ever expanding sphere of space at the speed of light (as do the gravitons representing the Sun's gravitational field) which hold the system's entropy increase in a 4.6 billion light year radius expanding sphere). So, leaving Earth out of it, the Sun's orb considered alone loses entropy in time while its huge closed system gains entropy via gravitons, neutrinos and light. Earth, while being a benefactor, is not much involved in this equation.

The Earth interior, while in constant motion (e.g. the convection of the rocky mantle and spin of the molten core) maintains a surprising equilibrium in temperature. The heat of the Earth interior derives from two sources: half the energy is heritage from its formation: accretion of planetesimals losing their kinetic energy to potential energy and friction (heat), and friction from differentiation (the friction from the denser stuff sinking). The other half of Earth’s interior heat comes (surprisingly) from the decay of radioactive elements in rock. The interiors heat is maintained and reradiated to space (see below) while the elemental decay decreases the Earth interior entropy. So again, the orb loses entropy while space gains IR radiation that more than makes up for this. As a surprise to most, sunlight does not keep the interior of Earth warm, just the surface.

The early surface of Earth cooled, sending enormous amounts of IR light into space, thus keeping the total entropy of the system increasing (radiation, as did the recent solidifying lava flow on Maui). The present Earth surface is warmed by sunlight, an effect which is greatly enhanced by the greenhouse gases: were it not for these gases, all surface water would be ice. These gases, trapping energy, keep the surface and air some 15 C hotter than otherwise. Absorbed sunlight warms greenhouse gases and us. All this energy constantly inflowing energy is constantly reradiated into space as infrared light to keep temperatures mostly in equilibrium. So solar energy in and IR energy out is almost constant and likewise is their entropy, except for two things: The isotopes in the interior are losing entropy and the Earth is radiating this entropy to space. Also, (and here is where the question is answered) solar power is used by processes on the surface, such as, Galileo like, to say, ripening grapes. All processes that make or construct (cities, houses, cars) generate heat which the Earth must radiate in IR light to space, which accounts for the growing entropy.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
re(2): and one thing furtherSteven Lord2018-07-10 16:18:46
re: and one thing furtherKenny M2018-07-10 08:00:48
and one thing furtherSteven Lord2018-07-10 02:45:44
re(2): again, not the solutionSteven Lord2018-07-09 23:55:22
re: again, not the solutionCharlie2018-07-09 21:38:18
again, not the solutionSteven Lord2018-07-09 20:44:59
solutionCharlie2018-07-09 19:39:10
Not the solutionSteven Lord2018-07-09 18:24:44
SpoilerKenny M2018-07-09 18:02:24
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