Is is the concern of geography to describe the physical characteristics of the earth – its size, its major features (like the continents and ocean basins), and its natural resources.
Nile River – Longest River in the World
Over 70% of the earth’s surface is water, most of which is ocean salt water. Actually, no boundaries divide the oceans; thus, there is really only one world ocean. It is customary, however, to divide this one large ocean into four big bodies of water – the Pacific, Atlantic, Indian, and Arctic oceans. The oceans are connected by straits (narrow bodies of water). Smaller parts of the oceans bodies of water). Smaller parts of the oceans are called seas, bays, or gulfs.
Rivers are usually formed in mountain or highland regions by melting snow and ice, runoffs from rain, and water from the underground springs. A river and its branches (or tributaries) form a river system. River systems empty into the sea. There place where the river starts is called its SOURCE; the place where a river empties into another body of water is called its mouth.
The total land area of the earth is approximately 57,280,000 square miles. It is divided into seven large masses called continents - Asia, Europe, Australia, and Antarctica. Islands are land forms that are smaller than continents and are completely surrounded by water. Greenland is the largest island. Peninsulas are tract of land that are nearly surrounded by water and are connected to a larger land form, usually a continent. The Iberian Peninsula, the Italian Peninsula, and the Balkan Peninsula are three large peninsulas in Europe.
The surfaces of continents and islands have different land forms. Geographers use elevation and relief to distinguish one land form to another. The four major type of land forms are mountains, hills, plains, and plateaus.
Mountains have a high elevation, usually 6,600 ft or more above sea level. They have a high relief (meaning, within a short distance, the elevation from one point to another may rise or drop greatly). Hills have moderate relief. Many hills are the remnants of mountains that have been diminished by erosion – the process by which water, wind, or ice slowly wears down land forms.
Plains are relatively flat or gently rolling lands. Their elevation and relief are usually less then 500 ft. Plateaus are also flat lands, but they have a higher elevation then plains – usually 1,650 ft or more. Plains and plateaus have relatively low reliefs.