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 ...

However, "blue-green algae are peculiar because they carry the common chlorophyll pigment, but also a second pigment called phycoerythrobilin," Cédric M. John, a professor and the head of data ...

This could explain why blue-green algae evolved both forms of photosynthetic pigments. Chlorophyll is best for white light which is the type of sunlight we have today.