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I heard that the Earth's atmosphere is opaque at most wavelengths and only allows visible light and radio waves through, so why have plants evolved to only absorb visible light?

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    $\begingroup$ @AlwaysConfused even humans don't use it naturally. I ain't sure, but as Alex says, there is probably no molecule which can release electrons by getting energy in RF range. $\endgroup$ – another 'Homo sapien' Sep 14 '16 at 12:46
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    $\begingroup$ Super low energy means super-low energy per single quantum. But even if we increase the intensity of radiation, i.e. higher rate of quanta-release at unit time, as well more total energy; yet it will remain inefficient to create reaction directly. $\endgroup$ – Always Confused Sep 14 '16 at 13:07
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    $\begingroup$ @AlwaysConfused some of your questions can be researched by googling. Also, comments on StackExchange are for discussing posted question, not other stuff like random ideas $\endgroup$ – aaaaa says reinstate Monica Sep 14 '16 at 18:20
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    $\begingroup$ Possible duplicate of Why do some bad traits evolve, and good ones don't? $\endgroup$ – kmm Sep 15 '16 at 1:57
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    $\begingroup$ @AlwaysConfused Comments are not for extended discussion. You can use the chat if you want. $\endgroup$ – WYSIWYG Sep 16 '16 at 5:12
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Even if the atmosphere is mostly transparent in the radio domain, most of sunlight is visible light.

Also, to make photosynthesis work, you need photons of high energy (say: wavelength shorter than 700nm) in order to excite electrons in the reaction centres. Radio waves cannot do that.

The most widespread photosynthetic organisms make use of visible light and water, which are plentiful on Earth.

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