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第1段
1 .Listen to part of a lecture in an anthropology class.
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2 .Okay, now we\'ve discussed how early modern humans used fire to cook food, a development from over 800,000 years ago. But what are some other ways that early humans used fire?
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3 .Do a pottery, like from clay that they heated up, or tools made out of metal?
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4 .Uh huh, pottery and metal tools. That\'s a good start.
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5 .Now here\'s the interesting thing. Remember, early humans started cooking about 800,000 years ago, right? Oh, and keep in mind that on this scale, these numbers are not exact dates. They\'re more to give us a general time frame for when certain advances occurred.
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6 .Anyway, pottery, or the earliest evidence of pottery appeared about 30,000 years ago, and metalworking was even more recent, only 5,500 years ago.
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7 .So what do you notice, given these dates? A gap, right, a pretty big gap between the developments of cooking and pottery making with seemingly no significant developments in the use of fire between them.
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8 .Well, that has all changed now thanks to some exciting findings by a researcher named Kyle Brown while he was working at Pinnacle Point in South Africa.
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9 .Pinnacle Point is a Stone Age site dating from about at least 72,000 years ago. Brown and his team of researchers found early tools with sharp, fine blades, perfect for tasks such as cutting animal skins to make clothes.
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10 .They were of such good quality, they may have even been traded, and these tools were made out of silcrete.
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11 .Silcrete is a hard rock made of silica, and the silcrete tools that were found were dark reddish-brown and highly glossy.
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12 .But when Brown began searching the areas near Pinnacle Point, he couldn\'t find any silcrete that had the same properties as the silcrete tools he found at the site.
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13 .The silcrete that Brown found around Pinnacle Point was yellow and dull.
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14 .It crumbled easily and was not good for making tools, so Brown was unable to account for where the silcrete tools at Pinnacle Point had come from.
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15 .That is until one day, Brown found a large piece of silcrete in what had once been a fire pit used by the early humans at Pinnacle Point.
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16 .It looked like it might have been accidentally dropped in the fire or maybe not. Most of the silcrete tools they found at the site were small, probably made by chipping small pieces off a larger rock.
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17 .So finding an unusually large piece of silcrete buried in ash, could this mean that the silcrete had been heated before being made into tools?
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18 .So to test his hypothesis, Brown conducted an experiment. He collected some yellow silcrete from the area around Pinnacle Point and heated it in a fire.
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19 .He found that not only was it easier to work with, it flaked rather than crumbled, but it looked exactly like the silcrete tools he had found at Pinnacle Point.
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20 .The mystery was solved. So why is all of this important?
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21 .First of all, the tools that Brown found were from at least 72,000 years ago, and represent a developmental step in the use of fire between cooking and pottery making.
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22 .But more importantly, the process that Brown had to follow to create his replicas of the stone tools was very complex.
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23 .First, he had to gather firewood and fuel for the project in advance, then bury some silcrete in sand and build a fire over the sand.
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24 .He had to gradually increase the temperature of the fire over a period of 12 hours,
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25 .then maintain a constant temperature for about five more hours, and then let the fire cool slightly so the stone didn\'t crack.
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26 .But once he did all this, he was able to create exact replicas of the tools he had found.
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27 .This complex process means that these early humans had advanced cognitive abilities, such as the ability to solve problems and plan ahead.
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28 .They also needed to have language, to communicate, to teach each other how to create these amazing stone tools.
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29 .Now, some of you might be wondering, could the tools have been burned unintentionally?
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30 .They could have been made from unbaked stone and then caught in a bushfire or something later on. I don\'t know.
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31 .I agree with Brown when he said that the greasy, shiny gloss on the thin blades proves that these were heated before being chipped off.
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