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This was covered pretty well in a PBS documentary (Nova, I think) that focussed on the back-tracking of human history via the Y chromosome. However, IIRC, they felt the drought, due to an Ice Age, was comewhat more recent than 70,000 years.

Dating is important as one major known catastrophic event happened at roughly that time. The most recent eruption of a super volcano, Toba in Indonesia happened about 75k years ago and blew a hole 60 by 18 miles wide and up to a mile deep there. Toba is by far the largest geologic event of the last 100k years. Shooting all that material into the atmosphere certainly messed up the world climate for several years. If this African drought happened right after Toba blew than look no further for its explanation. Also look no further than Toba for the reduced human population of that time that genetic research implies. It had to have a major effect on mankind at the time, but I don't think we have any human records, not even the legends of the Australian aborigines, that go back quite that far.

"However, IIRC, they felt the drought, due to an Ice Age, was comewhat more recent than 70,000 years."

See my post #24. It may have been the Last Glacial Maximum, the coldest period of the Ice Age.