Climate's role in Out of Africa 1

So now we've explored the route the first adventures took, lets take a closer look at what was going on with the climate. The reason why I'm devoting a blog post on this topic is that the changes in climate in the time period 1.8-2 ma (million years ago)  was one of the main factors enabling this migration of Homo erectus to occur.

The epoch we are looking at is the Pleistocene, it lasted from approximately 2.6 ma until 11,000 years ago and is characterised by a climate which fluctuated between cold glacial to warmer inter glacial periods. As the world slipped into a glacial period, huge ice sheets would descend from the poles and drape themselves across the Northern Hemisphere, locking away massive quantities of fresh water in the process.

Figure 1 Although it doesn't go right back to the period we're looking at this graph gives you an idea of the shifting climate occurring in the Pleistocene

Prior to the Pleistocene the climate had been relatively stable; in Africa grass lands were dominant and the rainforests had receded. It is interesting to note that this change can be determined by looking at the type of carbon that has been stored by the plants - C4 grasses are more dominant in arid environments and C3 leaves and plants prefer warm wet conditions. We use carbon dating amongst other methods to create a picture of the palaeoenvironment.

So anyway, the stage was now set for migration: resources were becoming scarcer, resulting in groups of Hominins having to travel further for their meals. There was only one problem - there was no way out of Africa. This all changed with the arrival of the glacial periods; the formation of ice requires large quantities of water, water which was sourced from the oceans. So much water was taken to form these ice sheets that sea level dropped by around 100m, opening up land bridges and allowing species to cross continents. In our case this land bridge was the Levantine corridor in Israel. Once H. erectus were across this land bridge they could spread onwards to conquour the rest of Asia and eventually a very chilly Europe.

Figure 2 Hominins in Europe