Assertion: desertification | /r/CapableOf | start in northwest china
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text: Various geological, geochemical and lithological methods used to study the geological ages of different desert areas in China indicate that desertification coincided with global climatic change, although estimates as to when desertification started in northwest China vary widely: early Tertiary, late Tertiary to early Pleistocene, late Pleistocene and early Holocene