Earliest Evidence of Anoxygenic Photosynthesis

Around 3.4 billion years ago, anoxygenic photosynthesis appears in rock evidence from the Barberton Greenstone Belt in South Africa. This process used hydrogen, hydrogen sulfide, or ferrous iron as electron donors instead of water and produced no oxygen. Molecular fossils and isotopic evidence indicate early bacteria evolved to capture light energy using non-water compounds. This metabolic development preceded oxygen-producing photosynthesis by hundreds of millions of years, allowing early microorganisms to harness solar energy before atmospheric oxygen transformation occurred.