[Lewis Thomson (OP)]

Donald has been pondering this question and seeks answers from The Naked Scientists,

"Photosynthesis is but one of the routes that energy begins to flow through living organisms. Chemosynthesis around deep sea volcanic vents is another, and is more likely to be more ancient. Are there any others?"

Can you help him find answers in the comments below?

[chiralSPO]

There are microbes that "eat" minerals via electrochemical means: https://www.quantamagazine.org/electron-eating-microbes-found-in-odd-places-20160621/

Also, while less interesting, there are plenty of life-forms that derive value from heat in their environment, especially sunlight. So, while not metabolically useful, lizards basking in the sun are able to use that energy to maintain their body temperature to facilitate their metabolism and other biochemical processes.

[evan_au]

Another source of energy is from natural nuclear radiation, ionising water.
https://www.livescience.com/4229-bacteria-2-miles-underground.html

There have been bacteria discovered living within the cooling water of operating nuclear reactors. I wonder whether they can take advantage of similar mechanisms?