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On earth, as far a we know, there are two main ways that bacteria gain energy.

  1. there is Photosynthesis, the transition of light into chemical based energies such as ATP.

  2. there are chemical processes in which the cell breaks down a variety of molecules to gain energy from the reactions. A example of this is Chemosynthesis.

Is it possible for there to be a bacteria or type of organism that gains energy from thermal energy?

For example, there could be a bacteria that lives in a volcanic area, somewhere hot enough that there is a excess of thermal energy. Would there be a way for such a cell to use this thermal energy in much the same way that some cells use sunlight in Photosynthesis?

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    $\begingroup$ Isn't this a thing on Earth? For instance in hydrothermal vents. Or are bacteria there using something different? $\endgroup$ – Denis de Bernardy Aug 6 '17 at 7:35
  • $\begingroup$ @Denis the heat certainly helps, but the bacteria at the bottom of the food chain feed off chemicals in the vent water. See divediscover.whoi.edu/hottopics/bacteria.html for an accessible explanation. $\endgroup$ – Spencer Aug 6 '17 at 11:43
  • $\begingroup$ You could extract energy at minus 100 degrees C... as long as you have minus 200 degrees C available too. It is not the heat itself that lets you extract energy... it is the heat gradient that allows you to do it. $\endgroup$ – MichaelK Sep 21 '17 at 8:15
  • $\begingroup$ As soon as AI on computers gets good enough that we would consider it life, a computer uses nothing but thermal energy, converted into electricity, and it spits out thermal energy. I was going to say that some type of liquid needs to exist for life, but if AI was ever considered life, imagine a solid state no moving parts computer, no liquid, all solid, and it would be considered life. $\endgroup$ – sthede Oct 24 '17 at 19:40
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It could be done, but it would be difficult. The trick is that you can't get usable energy from thermal energy directly. The only way to get usable energy from thermal energy is to find two areas with different temperatures, and transfer energy from hot to cold. This is what motors do.

A single celled organism like a bacteria would have a hard time generating energy. It would be much easier for a large colony to do this. I could see a colony taking advantage of the fact that particular reversible reactions are biased for at different temperatures. A colony may find a compound it can create at high temperatures, then pass out to low temperatures where the reverse reaction is preferred. This would generate usable energy by transferring the heat from hot to cold.

A single bacteria might be able to do this if there is a reliable thermal cycle. For example, if there was a major shift in temperature from daytime to night time, it might be able to hold onto those metabolites long enough to convert them one way during the day (generating energy), and then convert them the other way at night (also generating energy).

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    $\begingroup$ I was thinking about whether a organism can develop a mechanism to transfer heat from volcanos to cold places far away, possibly via conducting wire, similar to tree roots. But then I wonder how would this organism reproduce. $\endgroup$ – Ooker Aug 7 '17 at 4:35
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On a certain sense it already is, as the two processes you mention indirectly rely on thermal energy:

  • photosynthesis uses photons emitted via black body radiation by the sun
  • chemiosynthesis uses active chemicals generated thanks to high temperatures in volcanic areas and similar

Using directly thermal energy, and not via a chemical intermediate, is somehow tricky, since living cells as we know them are normally optimized to operate in a narrow ranges of temperatures, in which the achievable direct thermal energy is low (to directly use thermal energy one needs a high temperature source and a low temperature discharge).

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Please read about Carnot cycles and stuff. In order to utilize thermal energy, you need a hot and a cold "reservoir" or, in other words, a tempterature gradient and not just "high" temperatures. There are several problems with that when it comes to bacteria:

  1. Most cells are pretty small. There are exceptions, but your average microorganism will not be large enough to exhibit any singificant change of tempetature within it. Also it should only be able to live in a very small area and by drifting a bit might lead the entire organism to die because it's simply not made for those temperatures.

  2. If you find a way to deal with 1, you still need to consider that life as we know it needs liquid water. With a lot of salt, you can get let's say a range 140°C for water to be liquid, but no more is realistic if you want to permanently live in it. Mr. Spencer provided a reference in the comments: Some bacteria can grow at more than 113°C. Yes, microorganisms can survive pretty extreme conditions, but you cannot expect permanent temperatures much higher than that. So you have to be on the outside of the volcano where, coming back to point 1, the gradient will be much smaller than in the hotter zones. On top of that, you will almost certainly not find enough proteins that function properly in that entire range. A thermophile organism for example will not work at lower temperatures for that reason.

  3. It would have to evolve naturally with a pretty inefficient source of energy while a) Other live around it might have done it via the 2 options you named b) the environment it resides in is pretty unstable, a volcano isn't exactly a save place to live if you die from temperature changes and c) stuff wants to eat. Such an inefficient organism just doesn't make sense evolutionary. I think this becomes much more problematic if you make it bigger in order to compensate for the small temperature differences.

I could make a couple more points, but I'm running out of time. I'm not saying it is impossible, but you would have to adress those problems. Maybe you need to make up an organism that lives next to a volcano that touches a glacier.

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  • $\begingroup$ divediscover.whoi.edu/hottopics/bacteria.html - "temperatures well above 350C are not uncommon at [hydrothermal] vents." $\endgroup$ – Spencer Aug 6 '17 at 11:40
  • $\begingroup$ @Spencer I'm glad that we have a real world example that fits pretty well into my 140°C range for life. I was aware that certain organisms sustain pretty high temperatures, but not of the maximum they can prosper in. Thanks for the link! $\endgroup$ – Raditz_35 Aug 6 '17 at 11:45
  • $\begingroup$ @Spencer Included your link into my post $\endgroup$ – Raditz_35 Aug 6 '17 at 11:50
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As long as the first and second laws of thermodynamics are satisfied, then it would be possible in theory. This is a rather vague answer, but the organism would not be able to "live" if it just sat in an environment with a constant temperature. It might be able to go into dormancy in such a case, but dynamic activity would cease.

The organism will only absorb thermal energy if it's cooler than its local environment. Much of this absorbed energy will raise the temperature of the organism, and the rest will be used to drive chemical processes or modify the internal structure directly through thermal expansion/contraction. Some of these chemical processes may have an end result in the organism doing work on the environment or even on its own structure, but only if the first and second laws of thermodynamics can both be satisfied. These processes will stop when the organism reaches thermal equilibrium with its environment. In order to prevent the organism from eventually "cooking", it cannot just keep going warmer environments. It will have to eventually find itself in a local environment that's cooler than it is itself so that it can shed thermal energy, perhaps with the performance of more work. In order to meet any reasonable definition of life, the organism will have to find itself in an environment that oscillates thermally in order for it to create the structures and behaviors we would normally associate with life.

Unless the work the organism does is used to transport itself back and forth between warmer and cooler environments, it will have to rely on an external cause for the thermal oscillations.

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You might be imagining an organism, like a fungus or bacteria, that you can throw into a very hot environment. The heat would be "absorbed" and used by the organism, leaving less energy than before, essentially cooling it down. This organism would be incredibly convenient, and unfortunately breaks the laws of physics! It could be used to cool nuclear reactors and perhaps substitute for air conditioning if it were efficient enough. It would eventually reverse any kind of global warming.

I used quotes around the word "absorbed" because we don't have any way of doing that. Heat naturally flows from a high temperature area to a low temperature (moving to the state of maximum entropy: thermal equilibrium.) Moving thermal energy against this gradient require some kind of effort, which is inevitably going to increase entropy elsewhere.

High temperature areas like thermal vents also have high temperature gradients. Useful energy (mechanical or chemical) can be produced by a gradient in heat, but the reaction will always bring the whole system closer to thermal equilibrium.

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