Plant Life
During the Carboniferous and Permian periods, approximately 360 to 250 million years ago, vast swamps and forests covered much of Earth’s landmass. The decomposition and burial of this plant material, along with marine organisms, formed the organic deposits that would eventually become fossil fuels such as coal, oil, and natural gas. This accumulation of biomass represented an unprecedented concentration of carbon in the geological record.
Atmospheric Composition
The formation of these fossil fuel deposits fundamentally altered Earth’s atmospheric composition. As organic material was buried under layers of sediment, atmospheric oxygen levels rose significantly during the Carboniferous period, reaching concentrations higher than those present today. Conversely, carbon dioxide levels declined as plant material—which had extracted CO₂ from the atmosphere through photosynthesis—became sequestered underground rather than being recycled back into the atmosphere through decomposition. These atmospheric shifts had profound effects on global climate, ocean chemistry, and the evolution of terrestrial life.
The eventual uplift and erosion of these deposits over subsequent geological periods made fossil fuels accessible to humans, who would extract and burn them beginning in the Industrial Revolution, reversing millions of years of carbon sequestration in a matter of centuries.