This is a chronological map for that completely conjectural Green Sahara migration theory. The dates are all of real events, one date about the supposed Sahara migration to the Igbo area (5000 BP), is also estimated, and the 5500 BP date of migration to the east is also a theory. All these 'coincidentally' happened around the end of the Neolithic Subpluvial, or when the Sahara went dry.
In this theory, Megachad, the original size of Lake Chad, is probably the heart of the Sahara population.
More information about the theory see The Wet Sahara: A Practical Approach to the Question of the ‘Origin of the Igbo people?’