User:Robertinventor/Simple animals could live in Martian brines - Extended Interview with planetary scientist Vlada Stamenković: Difference between revisions

==Background information - historicalhistory contextof ideas of oxygen breathing life on Mars==

A historical 101 on multicellular life on Mars may be of interest here. First, of course back in the early twentieth century there was much speculation about oxygen breathing multicellular life there, with Lowell even speculating that intelligent Martians built the canals that he thought he could see in his telescope. By the time of early spaceflight it was already clear that the atmosphere was far too thin for terrestrial animals, but there was some hope for plant life. But the early observations from space showed a barren crater covered land and since then the idea of life on Mars has focused mainly on anaerobic microbes and photosynthetic life.

In 2014, however, researchers for DLR, Vera et al surprised many astrobiologists with their experimental result that multicellular lifelichens could bepotentially possiblegrow on present day Mars. ButThis is multicellular life, but only in the form of photosynthetic life able to produce its own oxygen. SomeThey took some lichens, such as {{w|Pleopsidium chlorophanum}} arethat were able to survive in close to Mars-like conditions high up on Antarctic mountain ranges, andsurviving only on the humidity in the air without any water. These did show promise in Mars simulation chamber experiments. They can do this because the algal component is able to make the oxygen needed by its fungal component. They can also do this without needing any extra water as intermediary, in the experiments they are able to grow in partial shade, using only the night time humidity of the atmosphere itself.

InIt principleis youalso couldpossible alsoto have microscopic (submulticellular millimeteranimals sized)that multicellularcan animalsmanage inwithout anoxicoxygen conditionsat all (sub millimeter sized). There are only a three species of suchthese creatures known on Earth, however, and they are not candidates for life on Mars. They are three species of {{W|Loricifera#In_anoxic_environment| Loricifera}}, tiny animals about the size of a large amoeba, are able to survive without oxygen in deep extremely salty mud sediments in the Mediterranean.<!--See sources in linked Wikipedia article and: Animals thrive without oxygen at sea bottom in background sources -->

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.

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.

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).