Until the 19th century, most of Africa was a mystery to the western world. Its impassable forests, rivers blocked by falls, enormous deserts, and deadly diseases had foiled explorers' attempts to infiltrate the interior. Little was known about the hundreds of groups of people who lived south of the Sahara in communities ranging from small villages to sprawling kingdoms. Nor was it guessed that our earliest ancestors took their first upright steps in Africa's heartland some four million years ago. Africa and the home of the lion elephant, the tall Watusi and diminutive Pygmy, the longest river and most giant dessert, was also the birthplace of humanity.
             Africa is a vast continent, second in size only to Asia, but few other geographical features are found on different continents. Its coastline has a relatively small number of inlets and peninsulas. Most of the continent consists of a vast high plateau that drops steeply to narrow coastal plains. Few mountain regions mark Africa, and those like the Atlas in the northwest are relatively small ranges or are isolated volcanic mountains, such as Mount Kilimanjaro. In addition, Africa's major rivers follow very irregular courses, and Africa's unique geological history explains these features. On a world map, Africa's West Coast and South America's east coast look as though they could fit together. That is because they once did. About 200 million years ago, the continents were part of a supercontinent called Pangaea. Africa lay in the southernmost part called Gondwana. About 180 million years ago, Gondwana broke away from Pangaea. Latter continent size chunks of land broke away from Gondwana and drifted away on tectonic plates. Some pieces collided with other plates and crumpled along their edges, forming long mountain chains. The African plate moved much slower than the others did, so it has no collision-caused ranges such as the Andes or the Himalayas.
             Sharp land drops called escarpmen...