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You're actually expecting too many similarities from life that would've evolved independently from Earth. If a certain metabolic pathway is only present in bact

by nnq 13y ago

You're actually expecting too many similarities from life that would've evolved independently from Earth. If a certain metabolic pathway is only present in bacteria in Earth's ecosystem, it doesn't mean that you could not find a very optimized version of it in bigger organisms in an independently evolved ecosystem. If you were from a world where photosynthesis is rare and not very efficient, or maybe not present at all in nature (like Europa's dark oceans?), you would probably assume that no large organisms could use such a weird and inefficient process as an energy source, whereas in an open sunlit ecosystem like Earth there are lots and lots of photosynthesizing organism. (I give the example of photosynthesis because it's actually a very complicated process: in order to achieve the kinds of efficiency that they do, the systems in plants and algae use very complicated mechanism that exploit even obscure quantum effects that are probably not used by any other biomolecular systems - there are studies using quantum tunneling to explain some properties of the molecules involved and others that talk about states similar to the ones in superconductors to explain some of the couplings and efficient energy conversions!)

gus_massa 13y ago
It's about universal chemistry rules. For example, it's very difficult to make a family of many complex stable molecules without carbon, so the "organic" chemistry of other words is probably based in carbon as our organic chemistry. Moreover, organic chemistry actually means "carbon based" rather than "life based". Many of these carbon bases molecules are built also by inorganic means in other words and in deep space. It's possible to make some complex molecules with boron and nitrogen, but most of them are not stable enough to bet your life on them. Other main detail is that you need some very energetic reactions, like combining the hydrogen in a molecule with oxygen to produce water. (The smaller example is CH4 + 2O2 -> CO2 + 2H2O, but methane is not easy to store, so most of the time earths life depend on the combustion of more complex molecules like sugars of fatty acids.) It's a matter using oxidations and reductions to obtain energy in a weight efficient way. Oxygen is easy to distribute, big organic molecules are easy to store and use in chemical reactions in controlled setting. So if you want to find whales, look for oxygen. In Earth's atmosphere is easy to find some strange non equilibrium mixing of oxygen from plants and methane from cows. (In any case, most of the oxygen and methane on Earth is probably produced by bacteria.) If you are really pessimistic, look for any anomalies in the spectrum. I checked Wikipedia http://en.wikipedia.org/wiki/Europa_(moon)#Potential_for_extraterrestrial_life http://en.wikipedia.org/wiki/Europa_(moon)#Potential_for_ext... . The article says that there are oxygen molecules in Europa! Mostly produced by the decomposition of water by the Sun's radiation. Someone estimated that the concentration of oxygen in water is enough to support fish equivalents, but it's an estimation not a measurement, and estimation are usually optimistic.

by nnq 13y ago

gus_massa 13y ago

It's about universal chemistry rules. For example, it's very difficult to make a family of many complex stable molecules without carbon, so the "organic" chemistry of other words is probably based in carbon as our organic chemistry. Moreover, organic chemistry actually means "carbon based" rather than "life based". Many of these carbon bases molecules are built also by inorganic means in other words and in deep space. It's possible to make some complex molecules with boron and nitrogen, but most of them are not stable enough to bet your life on them. Other main detail is that you need some very energetic reactions, like combining the hydrogen in a molecule with oxygen to produce water. (The smaller example is CH4 + 2O2 -> CO2 + 2H2O, but methane is not easy to store, so most of the time earths life depend on the combustion of more complex molecules like sugars of fatty acids.) It's a matter using oxidations and reductions to obtain energy in a weight efficient way. Oxygen is easy to distribute, big organic molecules are easy to store and use in chemical reactions in controlled setting. So if you want to find whales, look for oxygen. In Earth's atmosphere is easy to find some strange non equilibrium mixing of oxygen from plants and methane from cows. (In any case, most of the oxygen and methane on Earth is probably produced by bacteria.) If you are really pessimistic, look for any anomalies in the spectrum. I checked Wikipedia http://en.wikipedia.org/wiki/Europa_(moon)#Potential_for_extraterrestrial_life http://en.wikipedia.org/wiki/Europa_(moon)#Potential_for_ext... . The article says that there are oxygen molecules in Europa! Mostly produced by the decomposition of water by the Sun's radiation. Someone estimated that the concentration of oxygen in water is enough to support fish equivalents, but it's an estimation not a measurement, and estimation are usually optimistic.