differentiation may have been, or what elements of biological interest may have been lost to space as that differentiation took place.

Chemosynthesis may have occurred either at the present or in the past. Terrestrial chemosynthetic organisms take advantage of sluggish oxidation-reduction reactions as energy sources. Many redox reactions remain far from equilibrium owing to kinetic constraints, and life has evolved many ways of taking advantage of redox disequilibria involving iron, sulfur, carbon, nitrogen, manganese, arsenic, uranium, and other redox-sensitive elements. Redox reactions may also supply the chemical energy that could drive organic synthesis or the processing of organic compounds into primitive versions of biomolecules.

One test of whether Europa can support life is to identify whether there are sources of chemical energy available that are sufficient to drive metabolism. Measurements of the nature and abundance of chemical species within the water, the extent of any redox disequilibrium, and the abundance, if any, of organic molecules will help to determine the biological potential within the ocean.


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