<ul><li>Earth's oceans were not always blue, they were green for over 2 billion years.</li><li>Earth's earliest oceans had a green tint due to the presence of ferrous iron released by hydrothermal vent systems.</li><li>Cyanobacteria, the ancient algae, evolved phycobilins to absorb light in the iron-rich, green oceans.</li><li>The findings may help in understanding Earth's distant past and expanding the search for life in the universe.</li></ul>

Earth’s oceans weren’t always blue, scientists say

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