Jupiter's ocean moon Europa, thought to be habitable, may be oxygen-starved

Somehow we have an entire article about how a person can't walk around Europa without a helmet, as if it was news. The actual research is news, but it's about something completely different.

  Although the event is inferred to have constituted a mass extinction,[7] due in part to the great difficulty in surveying microscopic organisms' abundances, and in part to the extreme age of fossil remains from that time, the Great Oxidation Event is typically not counted among conventional lists of "great extinctions", which are implicitly limited to the Phanerozoic eon. In any case, isotope geochemistry data from sulfate minerals have been interpreted to indicate a decrease in the size of the biosphere of >80% associated with changes in nutrient supplies at the end of the GOE.

Makes you think of the sulphur dioxide in Venus' atmosphere, and whether life could still evolve in those conditions.

Getting the Carbon from CO2 gets the backbone of organic compounds. Getting the Hydrogen from H2O is also necessary and is also part of photosynthesis.

We have chemosynthetic bacteria on earth that use chemical energy rather than light. There is also a hypothetical biological process called radiosynthesis: https://en.m.wikipedia.org/wiki/Radiotrophic_fungus

I am not a biologist - but I find biology fascinating!

In the universe, and outer planets, yes. But the hotter (and smaller) inner planets have a hard time of keeping hold of lighter elements, so it's much rarer and only really available when bound to heavier compounds such as water.

1. Latent heat of formation. As the planet forms, denser materials sink down to the core and lighter materials float up to the top. This releases their gravitational potential, heating the planet. Over time though, this heat radiates into space. Icy moons are too old for this to be enough heat to support a liquid ocean.

2. Radioisotope decay. Particularly stuff like Potassium, on long time scales, decays and releases heat energy. This is a significant source of heating on Earth. Less significant on a small moon since radioactive isotopes are pretty rare, all things considered.

3. Solar heating. Sun hot. Planet kinda hot.

4. Tidal heating. The planet gets physically flexed by interacting orbital resonances between another moon and the host planet. This can be powerful enough to drive large amounts of volcanic activity on the surface of Io.

Europa Clipper is a mission that will fly high-precision magnetometers over Europa relatively soon (by NASA standards). It's possible that those magnetometers could pick up on induced magnetic fields from the interaction of charged salt ions moving in Europa's ocean with the magnetic field of Jupiter. If that signal can be detected, it may be possible to map the sub-surface ocean and start to do some sort of astro-oceanography.