Beer is one of the oldest drinks humans have produced. The first chemically confirmed barley beer dates back to the 5th millennium BC in modern-day Iran, and was recorded in the written history of ancient Egypt and Mesopotamia and spread throughout the world. As almost any cereal containing certain sugars can undergo spontaneous fermentation due to wild yeasts in the air, it is possible that beer-like drinks were independently developed throughout the world soon after a tribe or culture had domesticated cereal. Chemical tests of ancient pottery jars reveal that beer was produced as far back as about 7,000 years ago in what is today Iran. This discovery reveals one of the earliest known uses of fermentation and is the earliest evidence of brewing to date. Author Thomas Sinclair says in his book, "Beer, Bread, and the Seeds of Change: Agriculture's Imprint on World History" that the discovery of beer may have been an accidental find. The precursor to beer was soaking grains in water and making a porridge or gruel, as grain were chewy and hard to digest alone. Ancient peoples would heat the gruel and leave it throughout the days until it was gone. A benefit to heating the gruel would be to sanitize the water and the temperature required to denature grain proteins would also denature disease microbes. Leaving the gruel to sit would change it. Fermentation would occur and they noticed the change in taste and effect. Yeasts would settle on the mixture and rapidly consume the oxygen in the mixture. The low oxygen would force the yeast to digest sugars by anaerobic respiration. Then the yeast would release ethanol (alcohol) and carbon dioxide as by-products and, hence, beer was born. In Mesopotamia, the oldest evidence of beer is believed to be a 6,000-year-old Sumerian tablet depicting people consuming a drink through reed straws from a communal bowl. A 3,900-year-old Sumerian poem honouring Ninkasi, the patron goddess of brewing, contains the oldest surviving beer recipe, describing the production of beer from bread made from barley. In China, residue on pottery dating from around 5,000 years ago shows beer was brewed using barley and other grains. The invention of bread and beer has been argued to be responsible for humanity's ability to develop technology and build civilization. The earliest chemically confirmed barley beer to date was discovered at Godin Tepe in the central Zagros Mountains of Iran,