The African savannah landscape arose where climate was too dry and too cold to support a rainforest environment; thus, one may say the area of the savannah increased at the cost of a rainforest. After evolving over a period of several million years, finally, sometime after the middle of the Miocene period, the proportion of savannah grew equivalent to what we know it as today. Along with the evolution of the savannah came other important environmental changes that impacted its look and composition. Between Miocene and Pliocene periods, there was a decrease in atmospheric threshold for carbon dioxide, which caused a change of vegetation from C3 to C4 plants (grasses); thus leading to the expansion of the savannah.
This shows how the Savannah spread throughout Africa over millions over years, the numbers below the continent are in millions
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