Have you ever stopped to think where oxygen comes from? Your first thought may be a rainforest, but here’s a cool science fact for you: We can thank plant-based marine organisms for all that fresh air, according to the National Oceanic Service. Plankton, seaweed, and other photosynthesizers produce more than half of the world’s oxygen. While we may know the answer to this question, scientists still can’t explain these other ocean mysteries.