There are some very interesting links there. Here's just my opinion:
NASA seem to often flaunt the idea that there could potentially be hydrothermal vent systems in places such as Jupiter's moon Europa, based on evidence that there are cracks on the surface of this ice covered moon. The implication is there must be a warm core causing the ice covered surface to crack, move and refreeze driven by currents welling up from below causing the visual scarring so well documented by the Voyager probes, amongst others. Obviously Europa has an active core to create these currents, and hydrothermal vents must, therefore, exist. So far so good.
However, if one examines the hydrothermal vent fauna on this planet, practically every species seems to be a related to a surface living relative. Most of the animals that exist there seem to have migrated down from shallow surface waters over millions of years, slowly adapting and evolving to fit an increasingly hostile environment. So we have clams, crabs, shrimp and even octopi (Vulcanoctopus
), and not strange animals with unique body plans which is what one might expect if the community had truly evolved independently at the vent system.
Even the Riftia
tube worms, despite their unusual system of using sulphur fixing bacteria for energy are not unique; the animal has shallow water cousins that work in a similar manner. (Will try to find the reference, can't remember exactly where I read this).
So it seems, from my rather simplistic viewpoint, that in order for life to exist at hydrothermal vent systems, whether they be on Earth, Mars or Europa, the surface conditions must have been suitable for life to evolve first. I doubt if Europa ever had conditions even remotely favourable for the evolution of life, let alone complex life, being too cold and dark. Mars, well possibly, although we know the planet once had oceans, but the conditions now are very harsh. It stretches credibility to believe there could be a thriving system of complex life underground after hundreds of millions of years.
Even on earth, some of the the earliest fossils, stromatolites, evolved on the surface of the oceans absorbing nutrient from sunlight. This is why I have always been sceptical about these reports that complex life evolved at the hydrothermal vents and could exist elsewhere at these locations, if they exist, in the solar system. I seems to me that life moved
to the vents, not originated
Perhaps I'm talking cobblers. Believe me, I'd love to be proved wrong though!