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Analog examples of what primeval oceans might have looked in the Precambrian are probably extant in various regions
and at various size scales in present day oceans albeit they have not been sufficiently recognized and/or studied. The
Eastern Boundary Current Ecosystems (EBCEs), with their characteristic high productivity-inducing coastal upwelling
events, their extensive and intensive anoxic/hypoxic water column and methane and sulfide-rich benthic environment,
appear to represent such analogs. Moreover, recent studies have shown that they possess diverse anaerobic prokaryotic
communities of mat-forming large multi-cellular filamentous bacteria similar to fossils found in Archean and Proterozoic
rocks. Observations in the Bay of Concepcion, central Chile (~36°S), inserted in the second most productive EBCE of
the world, suggests that given similar oceanographic dynamics, past oceans may have presented different predominant
colorations after the first probable "red" color of the reduced iron-rich Archean ocean and prior to the present day
"blue" color. In this coastal ecosystem a "black" coloration has been observed to form as the result of the floating to the
surface layer of sulfide-blackened benthic detritus together with chunks of microbial mats, and a "milky to turquoise"
coloration resulting from different concentrations of colloidal, nano-sized particles which may include elemental sulfur
and/or microorganisms. If the present is the key to the past we posit that "black" color oceans could have existed during
the Proterozoic "Canfield sulfidic ocean" followed by "milky to turquoise" colored oceans during later stages of the
Proterozoic. Meso-scale examples of "milky" and "turquoise" portions of oceans, caused by elemental sulfur from
oxidized hydrogen sulfide eruptions, have been described from off Namibia and there appear to also exist elsewhere.
Examples of "black" oceans have apparently not been reported but the name of the Black Sea, the largest permanent
anoxic basin on Earth, suggests that at some point in time it may have been black, at least locally and/or for short
periods, prompting the name. We conclude suggesting that analogous to the present "Blue Planet" denomination, in the
past our Earth could possibly have deserved the successive names of "Red", "Black" and "Milky-Turquoise" Planet.
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