Carbonate rocks would release about 70 bars of carbon dioxide if heated, against a present carbon dioxide pressure of only 0.0005 bar. What does that comparison show?

1. Pressure measures how much gas is pressing down on each patch of surface. 2. The air today carries only 0.0005 bar of carbon dioxide. 3. The sedimentary carbonate rocks could give up about 70 bars if they were heated. 4. That store is more than a hundred thousand times the amount now in the air. 5. So almost all of the planet's carbon dioxide is held in the crust as rock, not in the sky. 6. The oceans hold water rather than the bulk of this carbon, so that option misplaces the store. 7. The early air was rich in carbon dioxide, so the claim that it held none is simply wrong. 8. Volcanoes only release gas that was already buried, so they are a doorway and not a store. _Source: OpenStax Astronomy (CC BY 4.0), section 8.3 Earth’s Atmosphere_