The arid landscapes of the Sahara and the darker vegetation of the wetter, semi-arid woodland known as the Sahel... The dark green marshes of Lake Chad stand out in the foreground. Even though it is more than 200 kilometers (120 miles) long, modern Lake Chad is just a small remnant of a vast lake that has repeatedly occupied the most of this landscape in the recent geological past. This lake basin stretches almost 1000 kilometers (600 miles) from the foreground of the image to the foot of the Tibesti Mountains.