For more than 400 years, sailors have reported a mysterious phenomenon in which the ocean appears to glow bright green […] ...

depending on the chemical makeup of the water. The abundance of iron and the flourishing of microbial life provide evidence for a green ocean. Blue-green algae, also called cyanobacteria ...

and future changes could shift ocean colors again. Earth is known as the “blue planet,” but a new study published in Nature suggests that our oceans may have once looked green instead of blue.