Changes in Earth’s Orbit May Have Turned Lush Region Into Sahara Desert

Subtle changes in the Earth’s orbit may have been responsible for the abrupt transformation of a large region of North Africa from a lush garden into the Sahara Desert. Radiocarbon dating shows that the changes occurred in two phases, one beginning 6,700 years ago and a sharper change beginning 4,000 years ago.

During those periods, temperatures rose and precipitation dropped sharply, German researchers report in the July 15 Geophysical Research Letters. During the last 9,000 years, they say, the Earth’s axial tilt decreased from 24.14 degrees to 23.45 degrees, and perihelion, the point in the Earth’s orbit closest to the sun, shifted from July to January, leading to the changes.

--Compiled by Times medical writer Thomas H. Maugh II