What natural resource is still mined today that was formed from the ancient oceans?

The correct answer is salt. Salt is a natural resource that is still mined today, and it has a geological formation linked to ancient oceans. Millions of years ago, when these oceans existed, the processes of evaporation and sedimentation resulted in the deposition of salt. Over time, as the oceans receded, these salts became buried and compacted, forming large deposits that can still be found and extracted today.

Salts are essential in various applications, from food preservation and seasoning to industrial processes and chemical manufacturing. In Michigan, significant salt deposits exist, notably in the form of rock salt, which can be mined through solutions mining or traditional mining methods.

While copper and iron have also been important resources in Michigan's mining history, they do not share the same direct connection to the ancient oceans as salt does. Sandstone is a sedimentary rock formed from accumulations of sand that have been compacted, but it is not primarily a mined natural resource like salt. Hence, salt is the most appropriate choice due to its direct formation from the deposition of minerals from ancient seas.