To illustrate the interaction between the atmosphere and the geosphere in the carbon cycle, a strong example would be the process of weathering of rocks.
When carbon dioxide (CO2) in the atmosphere combines with rainwater, it forms carbonic acid. This acid can then react with minerals in rocks in the geosphere, leading to chemical weathering. This process releases bicarbonate ions into the soil and waterways, which eventually can be transported to the ocean, where it can contribute to the formation of calcium carbonate in marine organisms.
This example effectively demonstrates how carbon from the atmosphere interacts with geological materials, showcasing the dynamic exchanges in the carbon cycle between these two spheres.