Changes in the Earth’s orbit that influenced the planet’s climate could lead to more humid corridors that allowed human migration from Africa to the Middle East, say researchers.
As revealed in a recently published study led by John Kutzbach of the University of Wisconsin-Madison, mankind may have moved out of Africa into the rest of the world thanks to climate change influenced by a change in Earth’s orbit.
The new paper describes a dynamic climate and vegetation model that explains when the regions of Africa, the areas of the Middle East, and the Mediterranean became wetter and drier and how the composition changed together, possibly providing migration corridors over time for populations to take advantage of.
“We don’t know why people move, but if the presence of more vegetation is helpful, these are the times that would have been advantageous to them,” Kutzbach revealed in a statement.
The model also explains the relationships between the Earth’s climate and its orbit, the concentrations of greenhouse gases, and its ice sheets.
For example, the newly proposed model reveals that around 125,000 years ago, North Africa and the Arabian Peninsula experienced an increase in summer monsoon rains that reached the north and narrowed the Saharan and Arab deserts due to the rise in grasslands.
At the same time, in the Mediterranean and the Levant (an area that includes Syria, Lebanon, Jordan, Israel, and Palestine), winter storm precipitation also increased.
These changes were driven by the position of the Earth in relation to the sun the new study has shown.
The northern hemisphere at that time was as close as possible to the sun during the summer, and as far as possible during the winter. This resulted in hot and humid summers and freezing winters.
“There was heavy summer rains in the Sahara and heavy winter rains in the Mediterranean,” explained Kutzbach.
Given the nature of Earth’s orbital movements, collectively referred to as the Milankovitch cycles, the region should be positioned in this way approximately every 21,000 years.
Approximately every 10,000 years or so, Earth’s northern hemisphere would then be at its furthest point from the sun during the summer, and much closer during the winter, explaining the abrupt changes in the climate experienced on Earth.
The model showed significant increases in rainfall and vegetation 125,000, 105,000, and 83,000 years ago, with corresponding decreases 115,000, 95,000, and 73,000 years ago, when summer monsoons declined in magnitude and stayed further south.
Between approximately 70,000 and 15,000 years ago, our planet experienced a glacial period and the model showed that the presence of reduced ice sheets and greenhouse gases increased Mediterranean winter storms, but limited the withdrawal of the southern summer monsoon.
The decrease of greenhouse gases also caused cooling near the equator, which generated a drier climate and reduced forest cover.
These developing regional patterns of climate and vegetation could have created gradients of resources for humans living in Africa, boosting migration to areas with more water and vegetation, helping them explore territories that were previously unavailable.