gen-define-the-carbon-cycle-in-rocks-and-give-one-short-worked-e-69bb

Define the carbon cycle in rocks and give one short worked example.

# Carbon Cycle in Rocks The **carbon cycle in rocks** (geological carbon cycle) describes the long-term movement of carbon through Earth's crust over millions of years. It involves: 1. **Weathering**: Atmospheric CO₂ dissolves in rainwater, forming carbonic acid that breaks down silicate rocks, releasing ions 2. **Deposition**: Carbon is transported to oceans where organisms use it to form calcium carbonate (CaCO₃) shells/skeletons 3. **Burial & Lithification**: Dead organisms accumulate on the seafloor and compress into sedimentary rocks (limestone) 4. **Subduction & Metamorphism**: Tectonic plates carry carbonate rocks into Earth's mantle where heat/pressure release CO₂ 5. **Volcanism**: CO₂ returns to atmosphere through volcanic eruptions --- ## Worked Example: Limestone Formation **Process**: Marine organisms extract dissolved carbon from seawater **Chemical reaction**: ``` Ca²⁺(aq) + 2HCO₃⁻(aq) → CaCO₃(s) + CO₂(g) + H₂O(l) ``` **Calculation**: How much limestone forms from 1000 kg of dissolved calcium ions? - Molar mass: Ca = 40 g/mol, CaCO₃ = 100 g/mol - Moles of Ca²⁺ = 1,000,000 g ÷ 40 g/mol = 25,000 mol - Moles of CaCO₃ formed = 25,000 mol (1:1 ratio) - Mass of limestone = 25,000 mol × 100 g/mol = **2,500 kg (2.5 tonnes)** This limestone locks away carbon for millions of years until geological processes release it.