We get oxygen primarily from photosynthesis carried out by various plants and organisms. The major sources of oxygen on Earth include:
- Oceans: The ocean is a critical source of oxygen, producing roughly half of the oxygen on Earth. This is mainly due to phytoplankton and other marine plants like seaweed and seagrass that photosynthesize and release oxygen.
- Phytoplankton: These microscopic photosynthetic organisms in oceans and rivers contribute about half of the oxygen we breathe, producing as much oxygen as all forests combined.
- Forests and other land plants: Though they contribute less oxygen than oceans and phytoplankton, forests (often called the "lungs of the Earth") and other vegetation also produce significant oxygen through photosynthesis.
Thus, most breathable oxygen comes from a combination of oceanic phytoplankton and terrestrial plants. The oxygen released over hundreds of millions of years accumulates in the atmosphere, enabling life.
