Describe three ways in which the presence of life has affected the composition of Earth’s atmosphere.

Oxygen Production: The most significant way life has affected the composition of Earth's atmosphere is through the production of oxygen. This is primarily done by plants, algae, and cyanobacteria through the process of photosynthesis. These organisms absorb carbon dioxide from the atmosphere and, using sunlight, convert it into oxygen and glucose. This process has led to the current oxygen-rich atmosphere that supports a wide variety of life forms.

Carbon Dioxide Reduction: In addition to producing oxygen, photosynthesis also reduces the amount of carbon dioxide in the atmosphere. This is important because carbon dioxide is a greenhouse gas that traps heat in the atmosphere, contributing to global warming. By absorbing carbon dioxide, plants help to regulate the Earth's temperature and climate.

Methane Production: Certain types of bacteria and other life forms produce methane, a potent greenhouse gas, as a byproduct of their metabolic processes. This includes bacteria in the guts of animals like cows and termites, as well as bacteria in wetlands and other anaerobic environments. While methane is less common in the atmosphere than carbon dioxide, it is much more effective at trapping heat, making it a significant contributor to global warming.