According to the Second Law of Thermodynamics (also known as the laws of conversation of energy and mass), anything is an isolated system cannot increase in complexity. For example, a wearing suit will eventually decompose.

Now we know the sun (and Earth mantle) is pumping energy into the system so the earth is not a closed system. However, the sun sends dangerous radiation that harms and even kills bacteria.

I am an advocate of evolution, but how can entropy begin when raw energy, unshielded from the sun, is ultraviolet light. As biological molecules require amino acids, proteins, DNA, and RNA is untenable when radioactive UV light kills simple bacteria.

I am well aware that the human body is a very complex machine. That is not the issue. My question concerns the first cell (inorganic material) from which life would sprout, as we know it. This inorganic material (soup that came alive) would not have been very complex at all. How did it survive the various heat of the sun in which all primitive life forms decay?

Source, please.

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    $\begingroup$ There are some misconceptions here. The second law of thermodynamics is not known as the "law of conservation of mass and energy". And the second law of thermodynamics makes no mention of the word "complexity". $\endgroup$
    – user40950
    Commented May 30, 2020 at 0:03
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    $\begingroup$ The second law of thermodynamics states that the change of entropy of an isolated system, under a physical or chemical process, is never a negative quantity. It is not an equivalent formulation for the energy and mass conservation laws. $\endgroup$ Commented May 30, 2020 at 2:54
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    $\begingroup$ In my opinion, the question should be rephrased, since what @Turk Hill wants to know is how did early life cope with UV radiation. There is not an special connection to entropy and thermodynamics. $\endgroup$ Commented May 30, 2020 at 2:58
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    $\begingroup$ If by everything you mean entropy, in regard to an isolated system, it increases with respect to time. $\endgroup$ Commented May 30, 2020 at 3:03
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    $\begingroup$ The blanket statement that UV kills bacteria is wrong, the huge number of earth bacteria that thrive in sunlight would be evidence of this. UV mostly just causes mutations, this could actually accelerate the evolution of early life. $\endgroup$
    – John
    Commented May 30, 2020 at 14:11

1 Answer 1


It's unclear how the laws of thermodynamics relate to the dangers of UV light in your question, but if I understand correctly your reasoning is the following:

1) The laws of thermodynamics say that order cannot increase in an isolated system, precluding life. 2) Life exists anyway because the Earth is not an isolated system: it receives energy from the Sun 3) Therefore, the energy received from the Sun is necessary for life 4) However, the Sun's rays also contain UV light, which would be fatal to primitive life forms 5) This leads to a contradiction, how do we resolve it?

The answer to the question as posed this way is that there is a flaw in items 2 and 3. It is true life needs inputs of energy to exist. It is also true the Earth receives energy from the Sun, and that this is the main source of energy that powers the modern biosphere. However it is not the only source of energy life can use to function; some organisms generate energy from chemical reactions such as the oxidation of hydrogen sulfide into sulfur. You yourself bring up "the Earth's mantle" as a possible source of energy, which is... The answer to your question :)


I believe it is generally agreed upon that however the first organisms got their energy they would not have used photosynthesis, and thus could perfectly well have developed away from sunlight and damaging UV radiation. See for example this article on the evolution of photosynthesis, which describes the consensus that it is a very ancient process that evolved not long after the origin of life:


Here is a hypothesis of the origin of life that suggests the first life used chemosynthesis, and in fact would have occurred in hydrothermal vents - about as far from sunlight as you can get:


  • $\begingroup$ I agree with what you stated, and it seems that early life developed far from the archean ocean surface, where UV radiation would be several magnitudes of order above the radiation you would get now. Early life must have survived in certain depths such that the radiation dose would be very low, atleast until DNA damage response mechanisms were developed. $\endgroup$ Commented May 30, 2020 at 14:56
  • $\begingroup$ Thank you for your answer. @LuisSierra I agree with what you wrote about the ocean. Oosaka, thank you again for sending the links. $\endgroup$
    – Turk Hill
    Commented May 30, 2020 at 17:50

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