growth, and persistence of iron bogs. Bog iron is a renewable resource; the same bog can be harvested about once each generation. Iron extraction Europeans developed iron smelting from bog iron during the Pre-Roman Iron Age of the 5th/4th–1st centuries BCE, and most iron of the Viking era (late first millennium CE) came from bog iron. Humans can process bog iron with limited technology, since it does not have to be molten to remove many impurities. Due to its easy accessibility and reducibility, bog iron was commonly used for early iron production. Early metallurgists identified bog-iron deposits by indicators such as withered grass, a wet environment, hygrophilous grass-dominated vegetation, and reddish-brown solutions or depositions in nearby waters. They stabbed wooden or metal sticks into the ground to detect larger ore-deposits, and cut and pulled back layers of peat in the bog using turf knives to extract smaller, pea-sized nodules of bog iron. Early iron-production from bog ore mostly occurred in bloomery furnaces. The resources necessary for production were wood for charcoal, clay for the construction of bloomery furnaces, and water for processing. Iron in the ore is reduced to a spongy iron bloom that stays in the upper part of the furnace while the undesirable elements stream downwards as slag. Smelting with a bloomery furnace often results in between 10 and 20 mass percent Fe being reduced to iron bloom, while the rest is transferred into the slag. The bloom must then be consolidated with a hammer to make usable wrought iron. There is some archaeological evidence that lime was added to furnaces to treat silica-rich ores that were difficult to smelt by the bloomery process. Europe First iron smelting attempts date back to the 2nd millennium BCE in the Near East. The technology then spread throughout Europe in the following two millennia, reaching Poland in the 2nd century BCE. Iron production reached Scandinavia around 800-500 BCE. Iron production sites in central Sweden are dated to the late Bronze Age and the innovation might have been transmitted from both the south and the east. The ore used was limonite in the form of red soil and bog ore. From 200 CE ore from limonite-deposits in lakes was used. The ore was reduced in bloomeries. There is evidence of a direct relationship between Viking settlements in Northern Europe & North America and bog iron deposits. Bog iron dominated the iron production