The ancient process that fuels your life and our fossil fuels

Science · Published 31 October 2026 Swipe more like this →

In short: Photosynthesis is more than just plants making food; it is a planetary engine of transformation. It converts light into the chemical bonds that sustain almost every food web on Earth, while simultaneously sculpting our atmosphere and providing the raw energy for modern industrial civilization.

Photosynthesis functions as a multi-stage biological system where autotrophs—including plants, algae, and cyanobacteria—convert light energy into chemical energy. In green plants, this occurs primarily within chloroplasts using pigments like chlorophyll a and b to capture specific spectra of light. The process is divided into two main phases: the light reaction and the Calvin cycle. During the light-dependent reactions, electrons are stripped from substances like water, releasing oxygen as a byproduct and creating essential molecules like ATP and NADPH.

The evolutionary history of this process reveals a complex lineage. While oxygenic photosynthesis (which releases oxygen) is dominant today, anoxygenic photosynthesis existed earlier. Some bacteria split hydrogen sulfide instead of water to release sulfur, while certain archaea may have used retinal pigments to create proton gradients as far back as the Paleoarchean. This suggests that the earliest forms of photosynthesis might not have been the oxygen-producing varieties we see in modern cyanobacteria.

The impact of these biological reactions on Earth's history is profound. The Great Oxidation Event, driven by photosynthetic cyanobacteria roughly 2.4 billion years ago, raised atmospheric oxygen to nearly 1 percent of current levels over 600 million years. This shift paved the way for multicellular life. Furthermore, the energy captured by plants millions of years ago was sequestered into the Earth's crust as fossil fuels—coal, oil, and natural gas. Modern civilization is now rapidly returning that ancient, sequestered carbon to the atmosphere in just a few centuries.

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