Archaeological and other scientific investigations have focused on the prehistoric exploitation of wild rice by humans, including: 1) the Anishinaabe, 2) so-called proto-Anishinaabe who may have later transformed into this culture from an earlier form, 3) other indigenous groups who exist today such as the Sioux people, and 4) archaeological-categorized cultures from the Initial and Terminal Woodland periods whose living lineages today are more difficult to identify. A seminal 1969 archaeological study indicated the prehistoric nature of indigenous wild rice harvesting and processing through radiocarbon dating, putting to rest argument made by some European-Americans that wild rice production did not begin until post-contact times. Researchers tested clay linings of thermal features and jigging pits associated with parching and threshing of the plant.