How does studying rocks and shells of aquatic organisms help scientists understand the history of Earth's climate?

Earths history of climate is easily understandable through the study of existing rock and shells aquatic organisms. Rocks came into the earth million of years ago. So, the study of age determinism of rock gives an idea of climate through which it has come across. This is called paleontology.  

Explanation:

In studying  Earth's history of climate scientists take help of available rocks and body parts of aquatic animals. As rocks are the most eventful findings on the earth's surface which has come across million of  years and witnessed several changes. These study if changes in rock is called paleontology.

Shells of aquatic animal which found in underwater are also a good evidence of earth's history of climate. It is found in the layers of sedimentary rock which is soft in nature and found in layerwise. Where all the organism became fossil after death and its body parts remains in the form of stone.