Were Earth’s oceans once green? 100Y Design/Shutterstock. ... But Japanese researchers have made a compelling case that Earth’s oceans were once green, in a study published in Nature.

Were Earth’s oceans once green? (Image credit: 100Y Design via Shutterstock) Nearly three fourths of Earth is covered by oceans, making the planet look like a pale blue dot from space.

If we discover a green-tinted world, it could mean that early photosynthetic organisms are thriving there, just like they once did on ancient Earth. Earth’s green oceans may be long gone, but ...

The reason Earth’s oceans may have looked different in the ancient past is to do with their chemistry and the evolution of photosynthesis. As a geology undergraduate student, I was taught about ...