Other extant ocean worlds in our solar system possess processes and characteristics similar to those that evolved and sustain life on Earth.

There are other ocean worlds in our solar system that may contain rock-water systems similar to those that could have given rise to life on Earth.

Processes unique to Earth make it the only ocean world in our solar system capable of evolving and supporting life.

Life on Earth likely began on land and not in the ocean, and abiogenesis required a unique combination of geologic, atmospheric, and orbital characteristics.
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Geologic Processes


Plate tectonic systems in ice can maintain redox disequilibria.

eTectonic systems in the shells of icy worlds can support redox gradients for life.


Lithic plate tectonics are required to maintain redox gradients over long time periods.

ePlate tectonics support long term life by recycling metabolic substrates.


Magnetic fields are required to maintain habitable environments.

eMagnetic fields support by geodynamos permit stable atmospheres and habitable surface environments.

Orbital Parameters and the Habitable Zone


Only bodies within a star’s habitable zone can host life.

eOutside of a star's habitable zone, planetary surfaces are either too hot or too cold for liquid water and life.

Initial Conditions


Chondritic planetary compositions provide the required elemental abundance for abiogenesis

eExtant ocean worlds in our solar system, such as Europa, accreted with similar initial chondritic compositions as Earth and have subsequently differentiated.


Other ocean worlds have ongoing rock-water interactions, akin to seafloor hydrothermal or terrestrial serpentinizing systems, where life may have begun on Earth.

eSome ocean worlds have pressure regimes permitting liquid water oceans in direct contact with silicate seafloors; others have high pressure ices with liquid or brine layers below which could support abiotic serpentinizing or hydrothermal seafloor alteration reactions.

ePlume material from Enceladus’ ocean contains H2, demonstrating ongoing hydrothermal alteration in an extraterrestrial sub-ice ocean.


Life on Earth began in the ocean, via serpentinizing or hydrothermal systems.

eHydrothermal systems on Earth produce reduced compounds such as H2 which supports abiotic production of CH4, and these processes are hypothesized as the early inorganic model for the evolution of ancient metabolism on Earth.


Life began in surface geothermal pools.

eOnly subaerial aqueous environments enable the condensation polymerization reactions critical for formation of complex organic molecules.

eHigh concentrations of ionic species in water, such as in seawater, inhibit assembly of proto-cell membrane structures.