What percentage of Earth's oxygen is produced by marine plants?

Marine plants, including phytoplankton, seaweeds, and seagrasses, play a crucial role in producing oxygen through the process of photosynthesis. It is generally estimated that marine plants contribute approximately 50% to 80% of the total oxygen available on Earth. While the specific percentage can vary based on several factors, the commonly referenced figure in many scientific discussions highlights that around 50% of Earth's oxygen is produced by oceanic sources.

The highest percentages in the choices, such as 75%, 85%, or others, might be overstated when considering the contribution from terrestrial plants and trees, which also account for a significant proportion of atmospheric oxygen production. Therefore, while marine plants are tremendously important, the most accurate representation of their contribution is roughly at the lower end of the scale, closer to 50%, rather than the highest option given.