Geologists study this history to find out how the earth looked in the past and how it has changed. Geologists are earth detectives. They piece together small bits of information to create the story of the earth. Geologists try to understand how rocks were created and destroyed. The events which shaped the earth are put in order, from oldest to youngest, to understand how the earth changed over time.
Geologists break time down into geologic time units called eras .
Each era contains smaller time units called periods . Check out our Minnesota geologic time table. The rocks were either destroyed, eroded away, or never formed. Without the rocks, it is harder for geologists to tell what was going on in Minnesota during these periods. The Division of Minerals is responsible for managing 12 million acres of state-owned mineral rights.