1. Formation of Calcium Carbonate
Investigation 5: Limestone
Earth History
Grade 6

2. Quick Write
In your ISN on page 74, titled “Limestone Fizz Quick Write”, please respond to the following question:
How do you think limestone forms? What process of sedimentation might produce a rock that fizzes with dilute acid?

3. Fizzing of Limestone
Limestone fizzes in acid because they contain calcite.
Calcite is one form of calcium carbonate.
The fizzing is CO2 (Carbon Dioxide) being releases.

4. Think About This…
Scientists want to know…
“Where does calcium carbonate come from, and how does it get into the limestone?”

5. Formation of Limestone
Calcium carbonate does not dissolve in water (H2O).
If calcium carbonate forms in the sea or falls into the sea, it will sink to the bottom forming a layer.
The layer turns to rock and the rock is limestone.

6. Where Does Calcium Carbonate Come From?
Calcium Carbonate forms in the sea in two main ways:

7. Where Does Calcium Carbonate Come From?
Type1:
Some animals use calcium to make their bones, shells, and scales.
The calcium in shells combines with carbon and oxygen to make CaCO3 (calcium carbonate).
When the animal dies, the calcium settles to the bottom and can be incorporated into the forming rock.
Example: Oyster shells can be a main component of limestone.

8. Where Does Calcium Carbonate Come From?
Type 2:
Calcium carbonate also forms when CO2 (carbon dioxide), exhaled by organisms living in the sea, reacts with calcium in the water.
Calcium carbonate forms right in the water and precipitates to the bottom.
Example: the reside at the bottom of our cups.

9. Calcium Carbonate Chemical Equation
Ca(OH)2 + CO CaCO H20