During the Carboniferous period, plant growth was extensive but rates of decomposition slowed (probably due to the formation of vast, oxygen-poor swamp habitats). As a result, large amounts of biomass accumulated in terrestrial environments (much of this biomass is now coal). The fossil record indicates that atmospheric oxygen increased, atmospheric carbon dioxide decreased, and global temperatures dropped. Explain why.

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1. During the Carboniferous period, extensive plant growth led to increased photosynthesis, which absorbs carbon dioxide (CO₂) from the atmosphere and releases oxygen (O₂). This process contributed to the rise in atmospheric oxygen levels.
2. The formation of vast swamp habitats, which were oxygen-poor, slowed down the decomposition of plant material. Decomposition typically releases CO₂ back into the atmosphere, so its reduction meant less CO₂ was being returned to the atmosphere.
3. With less CO₂ being released due to slowed decomposition, the atmospheric concentration of CO₂ decreased. CO₂ is a greenhouse gas, so its reduction contributed to a decrease in global temperatures.
4. The accumulation of plant biomass in these swamps, which eventually became coal, effectively sequestered carbon from the atmosphere, further reducing atmospheric CO₂ levels.
5. The combination of increased O₂ from photosynthesis and decreased CO₂ from reduced decomposition and carbon sequestration led to cooler global temperatures, as CO₂ is a key driver of the greenhouse effect.

Key Concepts

Carboniferous Period

The Carboniferous period, occurring approximately 359 to 299 million years ago, was characterized by extensive plant growth, particularly in swampy environments. This era saw the formation of vast coal deposits due to the accumulation of plant biomass, which was preserved in oxygen-poor conditions, slowing decomposition and leading to significant carbon storage.

Photosynthesis and Oxygen Production

Photosynthesis is the process by which plants convert carbon dioxide and water into glucose and oxygen using sunlight. During the Carboniferous period, the extensive growth of plants increased photosynthesis rates, leading to higher oxygen production. This contributed to a rise in atmospheric oxygen levels, as more carbon dioxide was converted into oxygen by the abundant plant life.

Carbon Sequestration and Climate Impact

Carbon sequestration refers to the long-term storage of carbon in plants, soils, and geological formations. During the Carboniferous period, the accumulation of plant biomass in oxygen-poor swamps led to significant carbon sequestration, reducing atmospheric carbon dioxide levels. This decrease in greenhouse gases contributed to global cooling, as less carbon dioxide was available to trap heat in the atmosphere.