A new study published by an international team of researchers led by Taro Matsuo, an astrophysicist at Nagoya University in Japan, argues that this evolutionary trend made sense 3 billion years when Earth’s oceans had a different color.

Although the Earth’s been decidedly blue for 600 million years, rising populations of phytoplankton caused by rising temperatures are once again causing the world’s oceans to turn green.

Earth's oceans may have been green for billions of years until the first photosynthetic organisms flooded our atmosphere with oxygen.