Earth is the third planet from the Sun. Earth is the largest of the terrestrial planet in the Solar System in diameter, mass and density. It is also referred to as the World and Terra.
Home to millions of Species, including humans, Earth is the only place in the universe where life is known to exist. The planet formed 4.54 billion years ago, and life appeared on its surface within a billion years. Since then, Earth's bioshpere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organism as well as the formation of the ozone layer which, together with Earth's Magnetic field, blocks harmful radiation, permitting life on land. The physical properties of the Earth, as well as its geological history and orbit, allowed life to persist during this period. The world is expected to continue supporting life for another 1.5 billion years, after which the rising luminosity of the Sun will eliminate the biosphere.
Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually migrate across the surface over periods of many millions of year. About 71% of the surface is covered with salt-water oceans, the remainder consisting of continents and island; liquid water, necessary for all known life, is not known to exist on any other planet's surface. mantle, a liquid outer coreinner core. Earth's interior remains active, with a thick layer of relatively solid that generates a magnetic field, and a solid iron 
Earth interacts with other objects in outer space, including the Sun and the moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365.26 solar days. The Earth's axis of rotation is tilted 23.4° away from the perpendicular to its orbital orbital, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. A cometary bombardment during the early history of the planet played a role in the formation of the oceans. Later, asteriod impacts caused significant changes to the surface environment.
Both the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to support a global human population. The inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth, and a modern perspective of the world as an integrated environment that requires stewardship. Humans first left the planet in 1961, when Yuri Gagarin reached outer space.
Source: http://en.wikipedia.org/wiki/Earth
A river is a natural stream of water, usually freshwater, flowing toward an ocean, a lake, or another stream. In some cases a river flows into the ground or dries up completely before reaching another body of water. Usually larger streams are called rivers while smaller streams are called creeks, brooks, rivulets, rills, and many other terms, but there is no general rule that defines what can be called a river. Sometimes a river is said to be larger than a creek, but this is not always the case.
