We call Earth the “Blue Planet” for a reason—but what if it used to be green?
A recent study out of Japan is flipping the script on what we thought we knew.
Their claim? Billions of years ago, Earth’s oceans weren’t blue—they were green.
Not because of algae blooms or pollution, but thanks to a whole lot of iron and a little thing called anaerobic photosynthesis.
Back in the Archaean eon, long before trees, whales, or Wi-Fi, Earth’s seas were loaded with dissolved iron.
Slowly Transforming The Planet
As the first microbes began using sunlight for energy, they produced oxygen—slowly transforming the planet.
That oxygen reacted with all the iron, forming oxidized particles that literally colored the water green.
“It’s like looking at Earth through a green-tinted lens,” the researchers suggest.
Modern blue-green algae, it turns out, thrive in similar iron-rich waters near volcanic islands like Iwo Jima.
And here’s the kicker—they use a special pigment that works best in green light.
This green ocean era lasted over a billion years.
And scientists say it’s a hint for finding life elsewhere—pale-green planets might be hiding alien microbes.
So yes, Earth’s oceans may have changed color before—and who knows, maybe they will again. Blue today.
Green tomorrow. Maybe even purple. The ocean’s true color story? Still being written.
