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User:Robertinventor/Simple animals could live in Martian brines - Extended Interview with planetary scientist Vlada Stamenković (edit)

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→‎Background information - why oxygen is so significant for multicellular life
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ThereAn isoxygen muchbreathing moreorganism energycan availableget tofar anmore organismenergy from the same amount of food with oxygen. Without oxygen, the {{w|Glucose|glucose}} that's the source of energy in Earth organisms can only be broken up into two {{w|Pyruvic acid|pyruvate}} molecules (each of 3 carbon atoms). This process produces two molecules of {{w|Adenosine triphosphate|ATP}}, the energy molecule that powers our cells. This worksis quicklya fast reaction, but the amount of energy it produces is limited;. it'sThis is the energy production method used in sprinter's "fast twitch" white muscle fibers. When Usain Bolt ran his 100 meters sprint he was relying on this chemical process. He wasn't really using much oxygen, mainly it was using up stores of glucose in his fast twitch muscles.
 
WithThis is not much use if you want to run a marathon however. Luckily for us, if you use oxygen, glucose can also be reduced all the way to carbon dioxide, and in the process {{w|Cellular respiration#Efficiency of ATP production|30 or 32 ATP molecules}} can be produced from a single molecule of glucose. This is the type of energy production used in the "slow twitch" red muscle fibers of a {{w|Marathon|marathon runner}}, or {{w|Ultramarathon|ultramarathon}} runner. It lets them run for many miles using little by way of glucose from their food. It amounts to (about 100 calories ofin excess calories over the resting metabolic calories, depending on body mass, or around 25 grams of glucose per mile, which in turn is derived from {{w|Glycogen|glycogen}} and then fat as the race progresses). In this way a large organism can sustain itself with little by way of food if it relies on oxygen.
[[File:Spinoloricus.png|thumb|This tiny animal, which never grows larger than a millimeter in size, is a species of {{w|Loricifera#In_anoxic_environment|loricifera}}, a rare multicellular anaerobe. Shown this colour because it is stained with Rose Bengal. Scale bar is 50 μm. In 2014, Carling et al. showed from general energetic considerations that should also apply to extraterrestrial carbon based life, that it is not easy for a food chain of anaerobes to sustain complex lifeforms even as large as 10 cms in diameter {{Image source|Danovaro et al.}}]]
WithoutA oxygenlifeform athat lifeformcan't woulduse oxygen needneeds to eat more than ten times as much food to get the same amount of energy as one that can use oxygen. It is hard for it to grow large because so much food is needed just to sustain itself and for reproduction. On Earth we don't know of any {{w|Anaerobic organism|anaerobes}} (organisms that can manage without oxygen) larger than those three species of {{w|Loricifera#In_anoxic_environment|loricifera}}, which are less than a millimeter in size. Anaerobes can buld large structures, as with the {{w|Stromatolite|stromatolites}}, which build up layer by layer but only the outermost layer, a thin biofilm, is actually alive.
 
It is possible for microbes to slowly build large structures without breathing oxygen, as with the {{w|Stromatolite|stromatolites}}, which build up layer by layer. However, only the outermost layer, a thin biofilm, is actually alive. Lichens of course do use oxygen, produced by the algal component. Trees and other plants produce oxygen but also use it at night.
What about extraterrestrial life though? Could it use something else in place of oxygen? Well, perhaps, but there is some earlier research that may suggest that it couldn't get very large. In 2005, Catling et al investigated the amount of energy available to carbon based organisms if with and without the use of oxygen in their metabolism. Oxygen produces the largest amount of free energy per electron transfer apart from fluorine and bromine, which are too reactive to build up in quantities useful to life. They found on general energetic principles that it still needs oxygen to sustain large complex lifeforms, from around 10 cms in size or larger. This is for any extraterrestrial food web for carbon based life.▼
 
▲What about extraterrestrial life though? Could it use something else in place of oxygen? Well, perhaps, but there is some earlier research that may suggest that it couldn't get very large. In 2005, Catling et al investigated the amount of energy available to carbon based organisms if with and without the use of oxygen in their metabolism. Oxygen produces the largest amount of free energy per electron transfer apart from fluorine and bromine, which are too reactive to build up in quantities useful to life. They found on general energetic principles that itextraterrestrial life would still needs oxygen to sustain large complex lifeforms, from around 10 cms in size or larger. This is for any extraterrestrial food web for carbon based life.
 
They worked it out by looking at how many smaller organisms are needed to support larger ones in the food web. For aerobic life the number of organisms in a food web is inversely proportional to the mass, if you are ten times heavier then there are ten times fewer of you in the food web. These numbers are much less for {{w|Anaerobic organism|anaerobes}}.
 
According to Catling et al's modeling, if an organism is a hundred times larger (and so a million times more massive), then organisms of that size are a million times less numerous in an aerobic food web, butthen the same size of organism isit's a billionmillion times less numerous in an anaerobic food web. So for instance, if (you'd have aonly 200one micronlarge organism preying on 20 micron organisms and they in turn on 2 micron organisms then there will be onlyfor a thousandthmillion ofsmaller the aerobic numbers in an anaerobic food chain. By the time you get to large organisms of 10 cm scale or larger they should be almost non existent in an anaerobic food webones).
 
Meanwhile an organism that's a hundred times larger in an anaerobic food web is a billion times less numerous in an anaerobic food web.
 
So for instance, if you have a 200 micron organism preying on 20 micron organisms and they in turn on 2 micron organisms then for a billion of the 2 micron organisms there will be a thousand of the 200 micron organisms in an aerobic food chain, but only one in an anaerobic food chain. By the time you get to large organisms of 10 cm scale or larger they should be almost non existent in an anaerobic food web.
 
So, ifIf Catling et al are correct in their inference here, then on general energetic principles that an extraterrestrial biosphere with large carbon based animals, at least of 10 cms scale or larger, is going to need oxygen. It seems to apply to Earth anyway. In anoxic environments, Earth animals have found it a challenge to get as large as 1 mm in size without oxygen, though it is possible that larger creatures lived on Earth when the seas were all anoxic.▼
 
Whether or not this applies generally to all extra terrestrial life, it does seem to apply to Earth life. In anoxic environments, Earth animals have found it a challenge to get as large as 1 mm in size without oxygen. It is possible that larger creatures lived on Earth when the seas were all anoxic before the Great Oxygenation Event. There are no surviving multicellular lifeforms from those times but they would be likely to be soft tissued and hard to preserve.
 
▲So, if Catling et al are correct in their inference here, then on general energetic principles that an extraterrestrial biosphere with large carbon based animals, at least of 10 cms scale or larger, is going to need oxygen. It seems to apply to Earth anyway. In anoxic environments, Earth animals have found it a challenge to get as large as 1 mm in size without oxygen, though it is possible that larger creatures lived on Earth when the seas were all anoxic.
==Technical details - guide to paper==
 
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