Monday April 14, 2025
Live Science —
Nearly three fourths of Earth is covered by oceans, making the planet look like a pale blue dot from space. But Japanese researchers have made a compelling case that Earth’s oceans were once green, in a study published in Nature.
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 the importance of a type of rock deposit known as the banded iron formation in recording the planet’s history.
Banded iron formations were deposited in the Archean and Paleoproterozoic eons, roughly between 3.8 and 1.8 billion years ago. Life back then was confined to one cell organisms in the oceans. The continents were a barren landscape of grey, brown and black rocks and sediments.
Rain falling on continental rocks dissolved iron which was then carried to the oceans by rivers. Other sources of iron were volcanoes on the ocean floor. This iron will become important later.