Researchers have pushed back the date of the earliest known alcoholic beverage repeatedly in the last few decades. In 1992, researchers led by Dr. Patrick E. McGovern Ⓒdiscovered chemical evidence of barley beer dating to around 3500-3100 BCE in Godin Tepe in western Iran. Four years later, chemical testing ⒷⒸconfirmed the presence of wine residue in two jars from another Iranian site, Hajji Firuz Tepe, which dates to 5400 BCE. In 2004, the beginning of the era of alcoholic beverages was pushed back to the seventh millennium BCE by the discovery of pottery in China that had contained a mixed fermented beverage of rice, honey, and fruit, the complexity of which hints at the existence of an even older brewing industry.
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Q13
According to paragraph 2, what makes some researchers believe that the first alcoholic beverages were produced earlier than the seventh millennium BCE?