Ronald Summers, age 11, of Philadelphia, Pennsylvania, for his question:
Was the Sahara really once a jungle?
Some 50 million years ago, magnolias thrived in the tropical climate of Alaska and crocodiles basked in the steamy rivers of the Dakotas. Every part of the earth has had a variety of different climates, somewhat like long chapters in a very eventful diary. Not so long ago in geological time, the hot and barren Sahara was indeed a thriving jungle. And farther back, this region had an even more dramatic change of climate.
Nowadays, the big thing in earth sciences is the theory of continental drift. Actually, most geologists now think there is enough evidence to accept this theory as fact. They assume that all the earth's land was once a single continent and investigate how and when this super continent broke up and drifted apart. We now know that the earth's crust gradually inches around like a loose skin, taking the geographic poles on slow, global tours. Some earth scientists suspected that about 450 million years ago, the South Pole was located in tile Sahara region of Africa.
Research teams investigated a number of places in this hot, arid desert. They probed into samples of its bedrock and examined rocky outcroppings exposed by the shifted sands. In January of this year, scientists from 11 nations arrived to survey the evidence on the spot. They agreed that 450 million years ago the South Pole was right there. At that time the present desert was buried under the south polar ice cap. Deep scratches gauged on its exposed rocks could have been made only by massive glaciers During this Ordovician Period of geological history, the ice cap extended 2,500 miles through Morocco and Mauritania, Algeria and Niger, Lybia and Chad.
The contrast between then and now is extreme. It makes it easier to believe that the Sahara also had a less dramatic jungle chapter in its past history. This chapter has been known to scientists for some time. Some of the best evidence was left by Neolithic people who lived there at least 10,000 years ago. They covered stony cliffs and whole hillsides with their sketches and colored paintings. And these early artists drew just about everything in the region.
They drew browsing giraffes and river hippos, deer and elephants and countless other jungle animals that depend on rich vegetation that requires plenty of water. Fossil evidence also proves that the region was inhabited by jungle animals during the ice ages of the past million years. One was a monster mastodon who must have needed at least a whole tree on his daily menu. The rivers that fed the region left their channels in the rocks. The Sahara enjoyed this thriving jungle climate fur perhaps a million years. Then, about 7,000 years ago, the evidence of this chapter begins to dwindle. The rivers and moisture dried up and, just before recorded history, the Sahara was remodeled to become the earth's largest desert at least for the present.
We have known for some time that the earth has been modeling and remodeling its features through more than four billion years. The continents and even the poles are slowly inching around the globe. Mountains rise and decline, ice ages come and go, seas invade the land and retreat. These events are more real to us when we survey the past chapers of the Sahara, or some other special region of the earth.