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.

Some cyanobacteria have pigments that specialise in harvesting green light to power photosynthesis, which may be because they evolved at a time when the oceans were iron-rich and green-tinged