One of Dr Weiss's former students, Sarah Parcak, of Cambridge University, presented data to the meeting on how a third period of cooling and drying, 4, 200 years ago, destroyed the Old Kingdom of Egypt.

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He also prepared period paints, thinned with benzene to accelerate drying.

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In the Middle East people started to build settlements as early as 15, 000 years ago, a period called the Early Natufian, but a drying of the climate made them nomadic again between 12, 800 and 11, 500 years ago.

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