How Photosynthesis Changed Earth

Photosynthesis changed Earth’s atmosphere and made complex life possible. It began about 3.4 to 3.8 billion years ago, when the first photosynthetic organisms used light energy to build organic compounds. These early organisms were anoxygenic phototrophs, which means they made food from light but did not release oxygen.

Photosynthesis, the process by which photosynthetic organisms convert light energy into chemical energy, likely began around 3.5 billion years ago.

The earliest form of photosynthesis was likely anoxygenic, using several alternative electron donors, such as hydrogen sulfide or ferrous iron, and releasing sulfur or oxidized iron rather than...