I was just wondering if it would be possible for a planet to have life that only uses noble gases in their biology. Like for example breathing in certain noble gases like Argon or Krypton for energy, or plants that react noble gases for energy and release other release noble gases.
Life requires metabolic pathways to create and store energy. Plants utilize sunlight to create carbohydrates through photosynthesis (a metabolic pathway) using ATP (adenosine triphosphate) as an intermediary.
Animals use carbohydrates from plants to create energy through aerobic respiration (a metabolic pathway) using ATP as an intermediary.
All the chemicals used in these reactions whether simple (oxygen, water, carbon dioxide) or complex(various proteins and various phosphorous-having organic molecules) have to be...well...reactive to have reactions.
Noble gases are not reactive. They do not form complex molecules, and I don't believe they form naturally occurring simple molecules either. Under laboratory conditions some compounds could be made, but the pressure and temperature requirements are challenging.
Without forming these molecules, I don't see how they can be used in any energy-creating or energy-storing reactions, not even as a catalyst.
Anything's possible. We don't really know what the required conditions are for life. That being said, it is extremely unlikely that life will use just noble gasses. For one thing, they just don't have any chemistry to speak of. They're called noble gasses because they don't react to form compounds in nature. In fact we didn't even think they were capable of forming compounds until the 1930s and never made one until 1962. Its just that hard to make them do it. Even then, they were reacted with strong oxidizers like fluorine and oxygen, which defeat your "only noble gasses" rule.
For reference, here's a complete list of every noble gas compound we've ever been able to construct in a laboratory. That's all of them.
This more of a conjecture than a full blown answer. Based on Cort Ammon's answer and my comment. So feel free to shoot me down in flames. For a biosphere to exist that based on noble gas chemistry the planet in question must have an extreme environment. It must be somewhere where "the pressure and temperature requirements are challenging" (to quote kingledion).
This suggests the environment must so extremely energetic that other chemical compounds will be volatile, labile and unstable. The environment must contain large amounts of noble gases either by mass or by percentage composition or possibly in terms of their chemical stability.
My first thought was a hot jupiter planet, but their environments may not be ionizing enough. My suggestion is the surface of brown dwarf.
While this isn't a planet the conditions in or on a brown dwarf might extreme enough to support the necessary high-energy chemistry for a noble gas compound biosphere.
This is simply a speculative train of thought. Most likely, it's completely wrong. But it would be possible to follow up different parts of the reasoning to see if they hold up to careful scrutiny.
These include the temperatures and pressures either on the surface of a brown dwarf or in the upper regions of its interior. The composition of elements in a brown dwarf to see if they meet the criterion of availability in the reasonably correct proportions for noble gas chemistry.
Other than under extreme pressures and temperatures, no noble gases create chemical compounds. One could, in theory, make biochemistry based on van der Waal interactions. These are forces that bring molecules together. This is a very exotic type of biochemistry if possible at all, as the noble gases involved would be in no set ratio and food may be just more gases absorbed into itself.
Alternatively, the biosphere could be made of noble gas plasma. According to Vadim Tsyovich's computer simulations, life could exist because of its electrical properties. The plasma self-organizes into a double helix and splits into daughter plasma-structures. Only the most stable of the organisms survive until they reproduce.