In general, two lines of inquiry have focused on archaeological wild rice: 1) The radiocarbon dating of charred wild rice seeds or the associated charcoal left behind during the parching stage of rice production, and 2) Examination of preserved wild rice seeds associated with specific prehistoric pottery styles found in excavations of processing sites. Different pottery styles in northern Minnesota are linked to certain times in the Initial and Terminal Woodland periods stretching from around 500 BC to the time of contact between indigenous peoples and Europeans. To place this in context, "Although ceramics may have appeared as early as 2,000 BC in the southeastern United States, it is about 1,500 years later that they became evident in the Midwest". After European contact, indigenous wild rice processors generally abandoned ceramic vessels in favor of metal kettles.