Final answer:
CO2 levels remained low during glacial periods due to natural processes like increased rock weathering, plant growth, and the formation of permanent ice sheets, which all worked to reduce atmospheric CO2 and the greenhouse effect, leading to a cooler planet.
Step-by-step explanation:
The levels of carbon dioxide (CO2) in the Earth's atmosphere have fluctuated throughout history due to various natural processes. These fluctuations have significantly impacted the global climate. During glacial periods, CO2 levels remained low, which led to less heat being trapped by the greenhouse effect, thereby cooling the planet. There are multiple factors that contributed to the reduced levels of CO2 during these times.
- One significant factor was the increased weathering of rocks due to the Sun's increasing luminosity, which led to a chemical reaction that removed CO2 from the atmosphere.
- Also, as plants began to spread on land, they absorbed more CO2, thus reducing the atmospheric CO2 concentrations.
- Furthermore, the formation of permanent ice sheets in Antarctica, driven by CO2 levels dropping past a critical threshold and changes in ocean circulation, helped maintain low CO2 levels during ice ages.
Measurements of CO2 trapped in the ice at places like the Vostok station in Antarctica have allowed scientists to observe these historical CO2 levels and their correlation with glacial and interglacial periods.