coal terminology. This classification designates oil shales as terrestrial, lacustrine (lake-bottom-deposited), or marine (ocean bottom-deposited), based on the environment of the initial biomass deposit. Known oil shales are predominantly of aquatic (marine, lacustrine) origin. Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil. Resource As source rocks for most conventional oil reservoirs, oil shale deposits are found in all world oil provinces, although most of them are too deep to be exploited economically. As with all oil and gas resources, analysts distinguish between oil shale resources and oil shale reserves. "Resources" refer to all oil shale deposits, while "reserves" represent those deposits from which producers can extract oil shale economically using existing technology. Since extraction technologies develop continuously, planners can only estimate the amount of recoverable kerogen. Although resources of oil shale occur in many countries, only 33 countries possess known deposits of potential economic value. Well-explored deposits, potentially classifiable as reserves, include the Green River deposits in the western United States, the Tertiary deposits in Queensland, Australia, deposits in Sweden and Estonia, the El-Lajjun deposit in Jordan, and deposits in France, Germany, Brazil, China, southern Mongolia and Russia. These deposits have given rise to expectations of yielding at least 40 liters of shale oil per tonne of oil shale, using the Fischer Assay. A 2016 estimate set the total world resources of oil shale equivalent to yield of of shale oil, with the largest resource deposits in the United States accounting more than 80% of the world total resource. For comparison, at the same time the world's proven oil reserves are estimated to be . The largest deposits in the world occur in the United States in the Green River Formation, which covers portions of Colorado, Utah, and Wyoming; about 70% of this resource lies on land owned or managed by the United States federal government. Deposits in the United States constitute more than 80% of world resources; other significant resource holders being China, Russia, and Brazil. The amount of economically recoverable oil shale is unknown. History Humans have used oil shale as a fuel since prehistoric times, since it generally burns without any processing. Around 3000 BC, "rock oil" was used in Mesopotamia for road construction and making architectural adhesives. Britons of the Iron Age used to polish it and form it into ornaments. In the 10th century, the Arab physician