The statue of liberty is made out of copper and was once shiny and copper-colored. over the years, the copper has gone through a process called oxidation, where it has changed into a new material. what has occurred?

A chemical reaction

Explanation:

What has ocurred in this situation is a chemical reaction known as oxidation.

To understand it better:

When the Statue of Liberty was sent as a gift from France to the United States in 1886, it was of a shiny reddish brown color, because its outer layer is copper of a thickness of two pennies put together (copper is a strong metal, so, this was not a problem).

However, years later, the outer layers of the Statue of Liberty reacted with the air (a natural chemical process due weather, called oxidation) forming a green-like layer of copper carbonate known as patina. This layer, in fact, protects the underlying copper layers from corrosion and degradation.