Final answer:
Oxygen is essential for most life on Earth and originated from the process of photosynthesis by cyanobacteria about 2.4 billion years ago. This led to the Great Oxygenation Event, dramatically changing Earth's atmosphere and enabling more complex life forms to evolve. Oxygen is also a byproduct of the photosynthesis process, which has inadvertently supported a diverse biosphere.
Step-by-step explanation:
Oxygen (O₂) is a colorless, odorless, tasteless gas that is essential for most forms of life on Earth. Its story begins with the Great Oxygenation Event, which took place about 2.4 billion years ago. This event marked the accumulation of free oxygen in our atmosphere, largely due to the photosynthesis performed by cyanobacteria. These organisms released oxygen as a byproduct, which ultimately led to the formation of the ozone layer and allowed more complex life forms to develop.
Initially, oxygen was not needed for life, as early conditions on Earth did not have free oxygen gas. However, after the onset of photosynthesis, oxygen levels in the atmosphere increased significantly. The excess oxygen had a dramatic impact, causing many organisms to go extinct due to their inability to handle reactive oxygen species (ROS). The survivors used oxygen to produce energy more efficiently through cellular respiration, a process that includes glycolysis followed by the Krebs cycle and electron transport, resulting in the production of ATP (adenosine triphosphate) in the presence of oxygen, also known as aerobic respiration.
Interestingly, oxygen can also be described as a waste product of photosynthesis. It is a 'leftover' from the reaction that converts carbon dioxide into carbohydrates, using the energy from sunlight. This 'waste' has been a boon for the development of life on Earth, as it supports a larger, more productive biosphere and enables biochemical reactions that were not possible before the increase in atmospheric oxygen levels.