When was the last time you thought about your breathing? Take a breath right now and think about it. You breathe because you need oxygen, a gas which makes up 21 percent of the Earth’s atmosphere. All that oxygen has to come from somewhere. You might already know that it comes from photosynthetic organisms like plants. But did you know that most of the oxygen you breathe comes from organisms in the ocean?

That’s right—more than half of the oxygen you breathe comes from marine photosynthesizers, like phytoplankton and seaweed. Both use carbon dioxide, water and energy from the sun to make food for themselves, releasing oxygen in the process. In other words, they photosynthesize. And they do it in the ocean.

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