From Earth's atmosphere, a carbon atom can go next to several key reservoirs or "sinks" as part of the carbon cycle:

• Biosphere : Carbon atoms in the atmosphere mostly exist as carbon dioxide (CO2), which plants absorb through photosynthesis to create energy and build organic molecules. This moves carbon from the atmosphere into living organisms

• Hydrosphere (Oceans) : Carbon dioxide from the atmosphere dissolves into the surface waters of oceans. It can be used by marine plants and algae for photosynthesis or can combine chemically to form carbonate ions, contributing to oceanic carbon storage

• Geosphere (Rocks and Soil) : Carbon can be transferred from the atmosphere to the lithosphere through processes like chemical weathering, where carbonic acid formed from CO2 and rainwater dissolves rocks. The carbon eventually forms sediments and sedimentary rocks such as limestone. Over long timescales, carbon is stored in rocks and soils

• Back to Atmosphere : Carbon atoms eventually return to the atmosphere through respiration, decomposition of organisms, volcanic eruptions, and human activities such as burning fossil fuels

In summary, from the atmosphere, a carbon atom can next enter the biosphere (plants and animals), the hydrosphere (oceans), or the geosphere (rocks and soil), continuing its cycle through Earth's systems