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From what I understand, Venus's upper atmosphere is much more habitable than its surface, with a temperature and pressure that humans could tolerate. However, lack of oxygen and the presence of sulphuric acid would likely kill most earth life. I would think plants could thrive on the abundant CO2 though if the acid did not kill them. I am curious if it is likely that purely airborne life exists in this zone of Venus's upper atmosphere?

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    $\begingroup$ Extremophiles could probably survive for a while in the upper cloud layers of Venus, but the interesting question is whether life could evolve there in the first place; I strongly doubt it. Lack of oxygen would not be a problem, though, as there is plenty of life on Earth to whom oxygen is toxic (methanogens) and keep in mind that life gave rise to the oxygen we have in our atmosphere. Main problem on Venus would be the absence of meaningful quantities of water and the absence of a strong magnetic field, assuming we're talking about life in the atmosphere, and not on the surface. $\endgroup$ – Happy Koala Feb 18 '17 at 15:37
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    $\begingroup$ To further the point: there would have to be liquid water in order for the necessary chemistry to take place. So, perhaps the question becomes: can life-evolving chemistry take place in a droplet of water of the size clouds are made of, is there a "sweet spot" in the Venusian atmosphere where water clouds can/do occur, and is there enough of it for enough "rolls of the dice" to get things going? $\endgroup$ – Anthony X Feb 18 '17 at 17:04
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    $\begingroup$ True, and the interaction between water and rocks in combination with a stable source of energy probably played a crucial role in life arising on Earth. I read a book called Life Ascending by Nick Lane in which he mentioned that microscopic cavities in rocks on the seafloor might have been the first cellular walls, so to say, which allowed the chemical reactions necessary for life to form to take place. Whether that's how it happened or not is anybody's guess, but I'm inclined to believe that you need rocks interacting with water in one way or another for abiogenisis to take place. $\endgroup$ – Happy Koala Feb 18 '17 at 21:48
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    $\begingroup$ The primary problem is that Venus is very dry. 20 ppm of water - 0.002% of the atmosphere. Far too little to support life, or form liquid water in any reasonable amounts. $\endgroup$ – SF. Feb 18 '17 at 21:53
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    $\begingroup$ Yea, I would like to add, though, that Venus might very well have hosted life in the early years of the solar system. Sun was colder, then, than it is today, and whatever gave Earth water probably gave Venus water, too. While I'm no betting man, I'd bet my hat that there's a higher likelihood of life having existed on Venus rather than Mars at some point in the history of the solar system. $\endgroup$ – Happy Koala Feb 18 '17 at 22:00
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I still would not bet on it, even with the recent detection of phosphine (see below). While the prospect is attractive because we would be able to search for this life without having to dig through anything, this question shows we are not yet ready to declare life likely in those clouds. Only the lowest level of planetary protection (that term means we avoid confounding or contaminating any possible life), which is really no protection, is called for on Venus today.

While the clouds of Venus have some intriguing features, AFAIK the kinds of complex organic compounds we normally associate with life, such as amino acids, are not known there (whereas we have seen such compounds on comets and in the plumes of Enceladus). Until this changes, Venus is a long shot for life.

Recently, phosphine has been detected in the clouds of Venus, and this is considered a possible biosignature because no known abiotic process forms it on terrestrial planets. This, however, does not of itself indicate the presence of life. We still must identify organic compounds unless we are prepared to suppose and test for some alternative, noncarbon basis for life. What the phosphine finding does is, it raises the stakes for finding such organic compounds. At this moment, scientists cautiously do not rule out "unknown" chemical processes for generating the phosphine, which itself is not an organic compound. Having organic compounds accompany the phosphine would make Occam's Razor more favorable to life. Engineers at Los Alamos National Laboratory are proposing to send an instrument to identify such organic compounds.

Readers who have knowledge about organic compounds on Venus should contribute to this question.

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For life as we know it, it is not likely it could exist !

Even bacteria need metal ions like $\text{K}^+$ and $\text{Mg}^{2+}$ in their cytoplasm, and these metals have not been detected in the atmosphere of Venus.

For life as we do not know it, we just cannot answer the question !

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    $\begingroup$ Is there much solid dust of any kind in the upper atmosphere there? I could imagine it being thrown up by vulcanism or lifted from the surface by winds. $\endgroup$ – Steve Linton Oct 5 '18 at 9:48
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    $\begingroup$ @SteveLinton This article hou.usra.edu/meetings/venus2014/pdf/6005.pdf mentions only iron of the metals measured in the middle and lower cloud. And it tells about the possibility of near-surface hazes, In the middle clouds there is the question of cloud condensation nuclei for the H2SO4, which could be meteoritic dust or vulcanic ash $\endgroup$ – Cornelisinspace Oct 5 '18 at 10:31
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If you want to go further, it is worth distinguishing between life can exist there and whether life could have arisen there. It is possible to say Yes to the first question and No to the second.

It is quite likely that life can’t arise on our Earth with its atmosphere full of poisonous oxygen but that, having arisen elsewhere (such as on the earlier oxygen-free Earth) it can learn to deal with that new environment quite well. You can allly a similar argument to Venus.

The first question is probably more interesting because more accessible to our thinking now without speculating on unknown details of primaeval events.

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It's possible.........but unlikely A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100 °C (212 °F) at sea level, but at 93.4 °C (200.1 °F) at 1,905 metres (6,250 ft) altitude. For a given pressure, different liquids will boil at different temperatures.

Venus is dry, because without water there's no universal carrying fluid for metabolism or dissolving of organic materials. Organic molecules require lower temperature condditions to create organic substances like proteins or DNA. Even with Venus high pressure; water boils at 365 degrees celsius. Venus is simply too hot for water; thus too hot for living things. Based on fundamental life chemistry water is the universal solvent and carrying fluid. Even up high where it's cooler.........there's the upper atmosphere is still hazardous. Venus has little magnetic field or ozone layer to fight off intense radiation. Being millions of miles closer to the sun, organic molecules would be destroyed

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