Answer :
Final answer:
The correct answer is option d) Rocks. Most of Earth's carbon, about 99.9 percent, is stored in rocks as carbonate minerals. The atmosphere, while containing carbon dioxide, does not hold the majority of Earth's carbon. Oceans and soils are also part of the carbon cycle, serving as significant reservoirs.
Explanation:
About 99.9 percent of all carbon on Earth is stored within the crust as calcium and magnesium carbonate in sedimentary rocks. Although the atmosphere contains recognizable carbon forms such as carbon dioxide (CO₂), it holds only a minute fraction of Earth's total carbon. The world's oceans are also major carbon reservoirs, mostly in the form of bicarbonate ions (HCO₃). Terrestrial rocks and minerals weather over time, releasing carbon into soils, contributing to the carbon cycle, which also includes deep Earth's carbon storage.
The biogeochemical carbon cycle highlights the movement of carbon through land, water, and air, displaying the complexity and varying speeds at which carbon is cycled through different reservoirs. Carbon reservoirs include the atmosphere, oceans, ocean sediment, soil, rocks (including fossil fuels), and Earth's interior. It is these reservoirs that hold carbon for extended periods until processes such as photosynthesis, respiration, decay, and combustion of fossil fuels release it back into the cycle.
