As an example, archaeologists divide human occupation of northeast Minnesota into numerous time periods. They are: the Paleo-Indian period from 7,000 years ago (5000 BC) extending back to an uncertain time after the glaciers receded from the last Ice Age; the Archaic period from 2,500 to 7,000 years ago (5000–500 BC); the Initial Woodland period from 2,500 to 1,300 years ago (500 BC–700 AD); the Terminal Woodland period from 1,300 to 400 years ago (700–1600 AD); and the historical period after that time. These rough dates are open to debate and vary by location in the state.