How plants turned a barren planet into a living world

Science · Published 27 October 2026 Swipe more like this →

In short: Photosynthesis is more than just plants making food; it is a sophisticated energy conversion system that built our atmosphere. By capturing photons and splitting water molecules, life on Earth fundamentally rewrote the planet's chemistry, creating the oxygen we breathe and the fossil fuels we burn today.

The process begins when chlorophyll captures photons from sunlight, initiating a complex series of energy conversions. Inside the leaf, Photosystem II splits water molecules to create oxygen as a byproduct, while Photosystem I works to produce NADPH. These components, along with ATP generated by the turbine-like protein ATP synthase, provide the chemical energy needed for the Calvin Cycle to transform carbon dioxide into glucose. This intricate system allows plants to convert minerals into organic compounds. The process is categorized into different types, including C3, C4, and CAM pathways.

This biological machinery changed the course of history approximately 2.4 billion years ago during the Great Oxidation Event. Driven largely by photosynthetic cyanobacteria, atmospheric oxygen levels rose to nearly 1 percent of current levels over a period of 600 million years. This shift in the biosphere paved the way for the evolution of most multicellular life forms, effectively creating the oxygen-rich environment we inhabit today. Without this continuous process, most life forms would eventually vanish. The biosphere would lose its foundational autotrophs, leading to a world devoid of oxygen.

The legacy of ancient photosynthesis persists in our modern world. Fossil fuels like coal, oil, and natural gas are essentially the remains of plants and small organisms that lived millions of years ago. These organic remains were deposited in the Earth's crust and protected from oxidation, where they were slowly converted into energy-rich compounds. Today, modern civilization is consuming these millions of years of accumulated photosynthetic production at an incredibly rapid rate, returning carbon dioxide to the atmosphere that was removed by plants in the distant past. These ancient deposits also serve as the primary raw materials for modern plastics. We are currently depleting this prehistoric energy surplus in just a few centuries.

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