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The desiccation of the Sahara and the associated neolithisation of West Africa is also cited as a possible cause for the dispersal of the [[Niger-Congo]] linguistic phylum.<ref name=Manning/><ref name=Kopytoff/>
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==Environment==
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{{Holocene}}
{{Main|Atlantic (period)}}
Based on studies by [[glaciologist]] [[Lonnie Thompson]], professor at [[Ohio State University]] and researcher with the [[Byrd Polar Research Center]], a number of indicators shows there was a global change in climate 5,200 years ago, probably due to a drop in solar energy output.<ref>{{cite web|url=http://www.news-about-space.org/story/2409.html |title=Major Climate Change Occurred 5,200 Years Ago: Evidence Suggests That History Could Repeat Itself |access-date=2004-12-17 |url-status=dead |archive-url=https://web.archive.org/web/20080115112153/http://www.news-about-space.org/story/2409.html |archive-date=2008-01-15 }}</ref>
* The [[Older Peron]] transgression was a period identified in 1961<ref name="fairbridge-1961">{{cite journal | last1 = Fairbridge | first1 = Rhodes W. | year = 1961 | title = Eustatic Changes in Sea Level | journal = Physics and Chemistry of the Earth | volume = 4 | pages = 99–185 | doi=10.1016/0079-1946(61)90004-0|bibcode = 1961PCE.....4...99F }}</ref> happening between 6,000 and 4,600 years [[Before Present|BP]] when sea levels were 3 to 5 metres higher than today.<ref>{{cite book|first1=Colin |last1= Murray-Wallace |first2=Colin |last2=Woodroffe |title=Quaternary Sea-Level Changes: A Global Perspective |publisher= Cambridge University Press|year=2014 |page=338|isbn= 9781139867153 |url=https://books.google.com/books?id=l13BAgAAQBAJ&q=%22Older+Peron%22&pg=PA328 }}</ref>
*Plants buried in the [[Quelccaya Ice Cap]] in the Peruvian Andes demonstrate the climate had shifted suddenly and severely to capture the plants and preserve them until now.<ref>{{Cite journal | last1 = Thompson | first1 = L. G. | last2 = Mosley-Thompson | first2 = E. | last3 = Brecher | first3 = H. | last4 = Davis | first4 = M.| last5 = León | first5 = B.| last6 = Les | first6 = D. | last7 = Lin | first7 = P. -N. | last8 = Mashiotta | first8 = T. | last9 = Mountain | first9 = K. | title = Inaugural Article: Abrupt tropical climate change: Past and present | journal = Proceedings of the National Academy of Sciences | volume = 103 | issue = 28 | pages = 10536–10543 | year = 2006 | doi = 10.1073/pnas.0603900103| pmid = 16815970 |bibcode = 2006PNAS..10310536T | pmc = 1484420 | doi-access = free }}</ref>
*c. [[3750 BC]] – The last North American [[mammoth]]s, on [[Saint Paul Island (Alaska)|Saint Paul Island]], [[Alaska]], go extinct.
*Tree rings from Ireland and England show this was their driest period.<ref name=SD5200>{{cite web |url=https://www.sciencedaily.com/releases/2004/12/041219142907.htm |title=Major Climate Change Occurred 5,200 Years Ago: Evidence Suggests That History Could Repeat Itself |work= [[Science Daily]]|access-date=19 December 2010}}</ref>
*Ice core records showing the ratio of two oxygen isotopes retrieved from the ice fields atop Africa's [[Mount Kilimanjaro]], a proxy for atmospheric temperature at the time snow fell.<ref name=SD5200/>
*Major changes in plant pollen uncovered from lakebed cores in South America.<ref name=SD5200/>
*Record lowest levels of [[methane]] retrieved from ice cores from [[Greenland]] and [[Antarctica]].<ref name=SD5200/>
*End of the [[Neolithic Subpluvial]], start of [[desertification]] of [[Sahara]] ([[35th century BC]]). North Africa shifts from a habitable region to a barren desert.<ref name=SD5200/>
*c. [[3150 BC]] a lesser [[Tollmann's hypothetical bolide]] event may have occurred.
*3051 BC [[Methuselah (tree)|The oldest currently (2013) living]] non-clonal organism germinated in the Grove of the Ancients.
==Calendars and chronology==
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