The Dawn of Photosynthesis and the Oxygenation of Earth: Around 2.4 billion years ago cyanobacteria emerged, the architects of the planet’s first photosynthetic processes. These microscopic prokaryotes harnessed the Sun’s energy, transforming it along with water and carbon dioxide into glucose and, crucially, oxygen. This period, known as the Great Oxidation Event, marked a dramatic increase in atmospheric oxygen levels, fundamentally altering the course of life’s evolution. Before this event, Earth’s atmosphere was largely devoid of oxygen, dominated instead by methane, ammonia, and other gases. 

Most life on Earth today consumes the Sun’s energy directly or indirectly, but not all life. Plants consume the Sun’s energy directly, plant eaters indirectly, and meat eaters one more step away. In addition to this chain of food, some life on Earth do not consume the Sun’s energy at all. Instead they consume nutrients found in extreme environments. Food to them like hydrogen sulfide.