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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? Uh huh, pottery and metal tools. That\'s a good start.
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4 .Now here\'s the interesting thing.
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5 .Remember, early humans started cooking about 800,000 years ago, right?
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6 .Oh, and keep in mind that on this scale, these numbers are not exact dates.
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7 .They\'re more to give us a general time frame for when certain advances occurred.
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8 .Anyway, pottery, or the earliest evidence of pottery appeared about 30,000 years ago,
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9 .and metalworking was even more recent, only 5500 years ago.
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10 .So what do you notice, given these dates, a gap, right,
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11 .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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12 .Well, that has all changed now thanks to some exciting findings by a researcher named Kyle Brown
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13 .while he was working at pinnacle point in South Africa.
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14 .Pinnacle point is a stone age site dating from about at least 72,000 years ago.
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15 .Brown and his team of researchers found early tools with sharp, fine blades
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16 .perfect for tasks such as cutting animal skins to make clothes.
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17 .They were of such good quality, they may have even been traded
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18 .and these tools were made out of silcrete.
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19 .Silcrete is a hard rock made of silica,
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20 .and the silcrete tools that were found were dark reddish brown and highly glossy.
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21 .But when Brown began searching the areas near pinnacle point,
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22 .he couldn\'t find any silcrete that had the same properties as the silcrete tools he found at the site.
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23 .The silcrete that Brown found around pinnacle point was yellow and dull.
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24 .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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25 .That is, until one day, Brown found a large piece of silcrete in what had once been a fire pit
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26 .used by the early humans at pinnacle point,
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27 .it looked like it might have been accidentally dropped in the fire
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28 .or maybe not. Most of the silcrete tools they found at the site were small,
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29 .probably made by chipping small pieces off a larger rock. So finding an unusually large piece of silcrete buried in ash.
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30 .Could this mean that the silcrete had been heated before being made into tools?
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31 .So to test his hypothesis,
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32 .brown conducted an experiment.
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33 .He collected some yellow silcrete from the area around pinnacle point and heated it in a fire.
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34 .He found that not only was it easier to work with, it flaked rather than crumbled,
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35 .but it looked exactly like the silk Creek tools he had found at pinnacle point.
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36 .The mystery was solved. So why is all of this important?
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37 .First of all, the tools that Brown found were from at least 72,000 years ago,
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38 .and represent a developmental step in the use of fire between cooking and pottery making.
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39 .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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40 .First, he had to gather firewood and fuel for the project in advance,
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41 .then bury some silcrete and sand and build a fire over the sand.
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42 .He had to gradually increase the temperature of the fire over a period of 12 hours,
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43 .then maintain a constant temperature for about five more hours, and then let. Let the fire cool slightly so the stone didn\'t crack.
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44 .But once he did all this, he was able to create exact replicas of the tools he had found.
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45 .This complex process means that these early humans had advanced cognitive abilities,
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46 .such as the ability to solve problems and plan ahead.
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47 .They also needed to have language, to communicate, to teach each other how to create these amazing stone tools.
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48 .Now, some of you might be wondering, could the tools have been burned unintentionally?
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49 .They could have been made from unbaked stone and then caught in a bushfire or something later on.
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50 .I don\'t know.
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51 .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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