Earth's Oceans Were Once Bright Green, New Study Suggests

Many poems and songs pay respect to our “oceans blue.” But a new study suggests they weren’t always that hue. Two billion years ago, they were more likely a vivid green. They may even change colors again.  

Researchers in Japan have found a link between the oceans of the Archaean Age (3.8-2.5 billion years ago) and the waters around Iwo Jima. It is an active volcanic island in the Pacific Ocean. Its waters are rich in sulphur and iron. This makes it ideal for blue-green algae. The algae are a type of bacteria. They turn Iwo Jima’s waters bright green.

Iwo Jima’s high iron levels are close to those found in all oceans in the Archaean Age. That, scientists say, suggests that there might've been lots of blue-green algae around the world. It might also help astronomers as they study outer space.

As we observe other galaxies, the colors of the planets may provide evidence of single-celled life forms, even if those colors aren’t the same as hues found on Earth. Red oceans may indicate the presence of bacteria that thrive in oxidized iron, for instance. Or a purple planet could reveal microorganisms that process sulphur. And, should the chemical makeup of our oceans shift as it did in the past, we may cease to be the solar system’s “blue planet.”

Reflect: How do you think it would impact the environment and ocean creatures if Earth's oceans changed color?

Gif of the ocean from GIPHY.