B.13C_Carbon_approaching – 03
Dinosaurs and other animals release carbon dioxide into the air. The carbon dioxide is a product of respiration that occurs in cells of living things. The carbon dioxide can circulate and reach the air above an ocean.
The carbon dioxide can be absorbed by ocean water at certain temperatures. The carbon dioxide dissolves in the water and forms carbonate. Marine organisms use the carbonate in the water to form shells. This connects carbon dioxide to shells.
The students must find out facts to connect the shells to chalk. In the museum’s hall of rocks and gems, they learn that chalk is a form of limestone. Limestone is made of calcium carbonate. It is formed mainly from the shells and bones of dead marine animals. As the animals die, they fall to the floor of the ocean. As time goes on, layers upon layers are packed on top of each other. Over millions of years, limestone is formed.
This completes the path of carbon from dinosaur to chalk. Carbon dioxide is exhaled. The carbon dioxide is absorbed by the ocean. The carbon dioxide forms carbonate in ocean water. Marine animals use carbonate to make shells. The shells and bones of dead marine animals settle at the bottom of the ocean. After millions of years, the layers form limestone, or chalk.

Carbon in limestone can remain stored for millions of years. It can enter the carbon cycle again when magma pushes through limestone during a volcanic eruption. The carbon dioxide that is given off during the eruption comes from the limestone. The carbon dioxide enters the air and can be used in the cycle again.