10. What would happen if oxygen were not available?

Without oxygen, aerobic organisms, including humans, would struggle to survive as our cells rely on oxygen for efficient energy production through cellular respiration. This would lead to a massive decline in populations of animals and humans, as we would have to depend on anaerobic organisms which generate energy less effectively. Decomposition would also slow down, leading to a buildup of organic matter since the processes require oxygen. In the grand ecosystem, plants and phytoplankton would also face a crisis. They not only contribute oxygen through photosynthesis but also depend on it for respiration at night. The resultant chaos would mean a drastic shift in the balance of life on Earth, likely favoring anaerobic bacteria and resulting in a very different world, replete with swamps and overgrown algae instead of lush forests.