A commodity market is a market that trades in the primary economic sector rather than manufactured products, such as cocoa, fruit and sugar. Hard commodities are mined, such as gold and oil. Futures contracts are the oldest way of investing in commodities. Commodity markets can include physical trading and derivatives trading using spot prices, forwards, futures, and options on futures. Farmers have used a simple form of derivative trading in the commodity market for centuries for price risk management. A financial derivative is a financial instrument whose value is derived from a commodity termed an underlier. Derivatives are either exchange-traded or over-the-counter (OTC). An increasing number of derivatives are traded via clearing houses some with central counterparty clearing, which provide clearing and settlement services on a futures exchange, as well as off-exchange in the OTC market. Derivatives such as futures contracts, Swaps (1970s–), Exchange-traded Commodities (ETC) (2003–), forward contracts have become the primary trading instruments in commodity markets. Futures are traded on regulated commodities exchanges. Over-the-counter (OTC) contracts are "privately negotiated bilateral contracts entered into between the contracting parties directly". Exchange-traded funds (ETFs) began to feature commodities in 2003. Gold ETFs are based on "electronic gold" that does not entail the ownership of physical bullion, with its added costs of insurance and storage in repositories such as the London bullion market. According to the World Gold Council, ETFs allow investors to be exposed to the gold market without the risk of price volatility associated with gold as a physical commodity. History Commodity-based money and commodity markets in a crude early form are believed to have originated in Sumer between 4500 BC and 4000 BC. Sumerians first used clay tokens sealed in a clay vessel, then clay writing tablets to represent the amount—for example, the number of goats, to be delivered. These promises of time and date of delivery resemble futures contract. Early civilizations variously used pigs, rare seashells, or other items as commodity money. Since that time traders have sought ways to simplify and standardize trade contracts. Gold and silver markets evolved in classical civilizations. At first, the precious metals were valued for their beauty and intrinsic worth and were associated with royalty. In time, they were used for trading and were exchanged for other goods and commodities, or for payments of labor. Gold, measured out, then became money. Gold's scarcity, its unique density and the way it could be