Evidence of life on Europa and Enceladus?

[Anomalocaris]

The water in lake vostok is practically fresh, being mostly melt water from the glacier above.

I agree that lake Vostok is fresh water, but I believe that prevailing thought is the lake was there before the glacier above it formed.

The water under the ice cover of Europa and Enceladus would be to be highly enriched in inorganic minerals, and is likely to be quite acidic or basic. There is good chance DNA won't survive in the water in Europa and Encledus.

Lake Voctok results suggests life can exist in cold, low light, ice conditions. But there are a lot more hurdles life must overcome before it can survive in the likely water conditions on the ice moons.

Enriched like the environment around a hydrothermal vent?

Relative to the majority of the deep sea, the areas around submarine hydrothermal vents are biologically more productive, often hosting complex communities fueled by the chemicals dissolved in the vent fluids. Chemosynthetic bacteria and archaea form the base of the food chain, supporting diverse organisms, including giant tube worms, clams, limpets and shrimp. Active hydrothermal vents are believed to exist on Jupiter's moon Europa, and ancient hydrothermal vents have been speculated to exist on Mars.

https://en.wikipedia.org/wiki/Hydrothermal_vent

I guess this means you don't care much for Iron–sulfur world theory?

I am all for Wächtershäuser's theory.

But there are detailed implications of the theory which makes it not quite so applicable to Europa and and Enceledus as one might think:

1. Evolved life on earth may readily take advantage of most of existing, magma powered hot hydrothermal vents on earth. Europa probably has this type of vents too. but Iron-sulfide world theory does not postulate that life can originate there.

2. Instead the theory postulate life started in another type of much cooler hydrothermal vent, called "white smokers", which has very different chemistry from the magma driven type. These vents are associated with rapid subduction, which requires plate tectonics. They are thought to have been abundant in archean era, but are very rare now on earth. Europa is not thought to have crustal plate tectonics under its ocean. So Europa probably doesn't have any crustal subduction or white smokers at all. So the Iron Sulfide world theory does not apply for how life could originate on Europa.

Having suitable environment for life to start is not the only issue. Because unlike the ocean on earth, which is open to air and separate chemical processes can occur on land, in the air and in the oceans to maintain a narrow range of ph value, Europa's oceans is global encompassing, and does not interact with any separate environment. So chemical interaction between rocks on Europa's sea floor and water in Europa's oceans over the life of the moon could have resulted in a highly acidic or basic water chemistry that is not condusive to survival of life.