What large, cold substance once covered the state of Michigan?

The large, cold substance that once covered the state of Michigan is indeed a glacier. During the last Ice Age, approximately 20,000 years ago, significant portions of North America, including Michigan, were covered by massive ice sheets known as glaciers. These glaciers shaped the landscape, carving out valleys, and creating features such as the Great Lakes. The weight of the ice also affected the underlying land, causing it to depress. As the climate warmed and the glaciers melted, they left behind various geological formations such as moraines, drumlins, and sandy plains, which are integral parts of Michigan's current landscape.

The other options are not applicable as water, while abundant in Michigan today, did not cover the entire state in the same manner as glaciers. Desert sand does not characterize Michigan's environment due to its temperate climate and abundant freshwater systems. While solid rock is present in the state, it does not represent the large-scale, cold coverage that glaciers did during the Ice Age.