Not the pond scum of Darwin’s theory, but real pond scum that exist here on Earth today, and that makes life possible for all of us. Marine algae, single celled photosynthetic plants, produce 70 to 80 percent of the Oxygen on the Earth. Thus without pond scum, we as Oxygen consumers, could not exist. Thus, it will be necessary to genetically engineer a type of photosynthetic algae for Europa, if it does not exist there already, and if the ice is not too thick to prevent the sun’s penetration.
Food for thought.