Geology Reference
In-Depth Information
About 5,500 years ago the rugged savannah country in north Africa vanished unbeliev-
ably fast. Whatever happened set the feedbacks off in the opposite direction towards
drying with exponential rapidity. Mathematical models suggest that a small change in
the earth's orbit led to subtle changes in the distribution of sunlight over the earth's sur-
face which were then amplified by long-distance teleconnections amongst sea ice, air,
ocean and vegetation in various parts of the world, as well as by the more local feed-
backs shown above. Modelling work combined with evidence from the field show how
these slight changes conspired to push the system across a threshold beyond which the
Figure 31: The rapid change from savannah to desert in North Africa 5,500 years ago. a: Change
in the amount of sunlight received in North Africa,
