Could plants on other planets not be green?

[Chronos]

Yes, all Earthly life needs nitrogen compounds, and yes, for those few organisms that do the fixing, the atmospheric nitrogen is relevant, but that’s why I said that the atmospheric nitrogen is irrelevant for most organisms.

[OtakuLoki]

@Stranger_On_A_Train

Absorbing X-rays is unlikely; UV is somewhat less so, although most life that we know cannot withstand large amounts of UV (but non-Earthlife may be more robust in this regard). Infrared is a possibility, but the problem there is the low energy plus the need to exhaust waste heat back to the environment, so that would have to occur in a very low temperature environment. Most likely phototropic organisms as we would recognize them as plant analogues would convert radiative energy in the visual spectrum.

Stranger

I thought that the atmosphere on earth was composed such that it leaves really only two wavelength “windows” for passing through EM radiation: One that corresponds roughly to visible light, and another that corresponds to what is called the radio spectrum.

If I’m correct about that, ISTM that terrestrial life evolved in a low-X-ray and UV environment. Which would indicate that there’d be little pressure to select for hardening to those wavelengths. If one posits a change in the spectra of radiation that are hitting our alien planet’s surface, so that more of the X-ray or UV energy is coming through - I believe that could provide evolutionary pressures to harden organisms to those kinds of radiation.

FTM, wasn’t there a recent discovery of an organism using melatonin to capture relatively higher energy photons for photosynthesis inside the ruined Chernobyl reactor facility? IIRC by collecting the energy from such radiation for photosynthesis, the organism was, at the same time, reducing the biological damage it was taking from the radiation. So, it seems to me that properly tuned photosynthetic dyes could act to help protect the rest of the organism from the effects of X-rays.

[Stranger_On_A_Train]

@OtakuLoki

If I’m correct about that, ISTM that terrestrial life evolved in a low-X-ray and UV environment. Which would indicate that there’d be little pressure to select for hardening to those wavelengths. If one posits a change in the spectra of radiation that are hitting our alien planet’s surface, so that more of the X-ray or UV energy is coming through - I believe that could provide evolutionary pressures to harden organisms to those kinds of radiation.

The problem is that protein-based structures that make up life as we know it don’t tend to survive long enough in high energy (UV and above) environs to even develop protection. Most viruses, for instance, (while not technically alive) are quickly destroyed by exposure to ultraviolet. I highly doubt that any kind of organism that we could conceivably recognize would be able to resist or absorb X-rays. This doesn’t mean that some form of self-organizing and -replicating, thermodynamically auto-regulating criticality couldn’t fit in this environment, but I don’t think it would look anything like “life” as we conceive of it.

@OtakuLoki

FTM, wasn’t there a recent discovery of an organism using melatonin to capture relatively higher energy photons for photosynthesis inside the ruined Chernobyl reactor facility? IIRC by collecting the energy from such radiation for photosynthesis, the organism was, at the same time, reducing the biological damage it was taking from the radiation. So, it seems to me that properly tuned photosynthetic dyes could act to help protect the rest of the organism from the effects of X-rays.

This is true, but again, the organism had already evolved the capacity to make melatonin–a fairly complex hormone that is used in numerous roles in metabolism–and was adapting to a new environment. Also, don’t get the impression that it was directly absorbing gammas or x-rays; it was absorbing daughter products from scattered radioactivity. X-rays are too energetic to be safely absorbed by anything “organic”, i.e. carbon-backbone structures or nucleic acids.

Stranger