World
The Earth is the first planet known to have liquid water on the surface and is the only place in the universe known to harbor life. Earth has a magnetic field that, together with a primarily nitrogen-oxygen atmosphere, protects the surface from radiation that is harmful to life. The atmosphere also serves as a shield that causes smaller meteors to burn up before they strike the surface.
Lake
A lake (from Latin lacus) is a body of water or other liquid of considerable size contained on a body of land. A vast majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes. In ecology the environment of a lake is referred to as lacustrine.
Lakes have numerous features in addition to lake type, such as (but not limited to) drainage basin (also known as catchment area), inflow, and outflow, nutrient content, dissolved oxygen, pollutants, pH, and sedimentation.
Sea
A sea is either a large expanse of saline water connected with an ocean, or a large, usually saline, lake that lacks a natural outlet such as the Caspian Sea and the Dead Sea. The term is used colloquially as synonymous with ocean, as in "the tropical sea" or "down to the sea shore", or even "sea water" to refer to water of the ocean.
Mountain
A mountain is a landform that extends above the surrounding terrain in a limited area. A mountain is generally steeper than a hill, but there is no universally accepted standard definition for the height of a mountain or a hill although a mountain usually has an identifiable summit.
The altitude of mountains means that the tops exist in higher cold layers of the atmosphere. They are consequently often subject to glaciation and erosion through frost action. This produces the classic mountain peak shape. Some mountains have glacial lakes, created by melting glaciers; for example, there are an estimated 3,000 in Bhutan.
Ocean
An ocean (from Ωκεανός, Okeanos (Oceanus) in Greek) is a major body of saline water, and a principal component of the hydrosphere. Approximately 70% of the Earth's surface (an area of some 361 million square kilometers) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.
River
A river is a natural waterway that transits water though a landscape from higher to lower elevations. It is an integral component of the water cycle.
Rivers have been used by man since the dawn of civilization as a source of water, for food, for transport, as a defensive barrier, as a source of power to drive machinery, and as a means of disposing of waste.
Desert
In geography, a desert is a landscape form or region that receives very little precipitation. Deserts are defined as areas that receive an average annual precipitation of less than 250 mm (10 in).
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