Since life converts matter to energy, and there's no natural process that does the opposite (aside from supernovas), does this mean that the mass of our planet is gradually diminishing? I asked ChatGPT, but it's dumb as rocks, and this question has lingered in my mind for years, so I'd appreciate an answer from someone who knows their stuff.
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$\begingroup$ Hi Lynx. Welcome to Phys.SE. Did you try to do a back-of-an-envelope estimate? $\endgroup$– Qmechanic ♦Commented Jun 23 at 10:12
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$\begingroup$ Supernova synthesis of heavy elements is not the only endothermic process. $\endgroup$– PM 2RingCommented Jun 23 at 10:39
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2$\begingroup$ What process do you mean when you say "life converts matter to energy"? Humans do it using nuclear fission, but that's the only example I can think of. $\endgroup$– matt_ruleCommented Jun 23 at 17:47
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2$\begingroup$ Photosynthesis does create mass from energy. The masses involved are tiny, but they're not zero. The same mass is lost when respiration splits the sugar. $\endgroup$– Jack AidleyCommented Jun 23 at 18:16
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$\begingroup$ Not to mention that cosmic "dust" as well as meteorites are adding mass all the time -- and that the actual mass loss of Earth is primarily due to upper atmospheric escaping. $\endgroup$– Carl WitthoftCommented Jun 23 at 21:58
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2 Answers
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Remember that nearly all of life's energy ultimately comes from the sun. Life uses energy that is received from the sun, "mixes" it with matter from the earth, and eventually that energy gets radiated back into space as heat. So no energy is lost because if life depends on sunlight.
Some life forms, like the bacteria near "black smokers" use energy that ultimately comes from the earth's internal heat. Part of this heat is generated by the decay of radioactive elements, more comes from the heat of earth's initial formation. All of this energy would escape regardless of the existence of life. So you could say that a minute fraction of earth's mass is lost - but not because of life, it would disappear with or without life.
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Good question! No, life does not reduce the mass of Earth. Life is cycling elements such as C, O, N and H. It is fuelled nearly completely by solar energy. This is converted to heat, which at the end leaves Earth as thermal radiation. I neglected the contribution of the binding energy of biomolecules and fossil fuel, which actually reduces the mass of Earth.
