What is the Meaning & Definition of land

The Earth is the third planet of the solar system (taking into account its distance from the Sun, 150 million kilometers) and despite the fact that it was formed at the same time that the Sun and the rest of the system hosting, 4,570 million years ago is the only planet in which so far has proved that there is life.
After successive controversies, dimes and bickering and some more complicated issues which occurred in some moments of history (middle ages), such as persecution against those who argued a position or a different view of the established order, precisely in historical periods in which was not well seen, came to the conclusion that the shape of the Earth is geoid similar to a sphere but flat. In this way, was discarded what the first cultures argued about the format of the planet as "Earth flat", giving the right to several astronomers and philosophers such as Plato and Aristotle, who thought that it was round. On the basis of this suspicion of the sphericity of the Earth, Eratosthenes had been able to calculate the diameter of the planet with negligible error. In addition, many civilizations not European, some Asian peoples and cultures of Mesoamerica, gambled with the sphericity of the Earth already in ancient times. However, in the 16th century recently could be demonstrated this hypothesis through around the world undertaken by boat Juan Sebastián Elcano, as surviving captain of the journey started by Magellan.
8 planets currently seen in the solar system, Earth is defined as the greatest of solid planets, with 12756 km from Equatorial diameter, thus beating Venus, Mars and mercury, in that order of volume. It is also the only one that has a single natural satellite (Moon), the remaining planets have already with at least 2 moons (as Mars) either have no satellites, as it is the case with mercury or Venus. It is worth to remember that Pluto is not currently considered a planet, but a celestial body at an intermediate level (dwarf planet or plutoid).
The Earth is made up of four large areas or layers: the lithosphere, the hydrosphere, the atmosphere, and the biosphere; Meanwhile, it is the only planet that owns 71% of its surface covered by water. This situation is that explains the color blue and also undoubtedly have allowed the development and survival of the living species that inhabit it. Another peculiarity is the ability of homeostasis presenting this and thanks to this property may recover from the worst natural disasters in a very short time. It is also the only celestial body of the solar system whose atmosphere describes a predominance of nitrogen and oxygen, which is ideal for the growth and development of human beings.
And respect of their movements, studies have shown that the Earth has at least two movements: the translation, which is the movement around the Sun, and the rotation, which consists of a change of direction. The phenomenon of translation is done on an elliptical orbit and takes an approximate total of 365 days, which gives rise to a calendar year and the 4 seasons as we know them. On the other hand, the process of rotation is the rotation of the planet on a hypothetical shaft, which is completed in a period of approximately 24 h and is considered responsible for the sequence of the day and night. Stands that Moon does homologous movement relative to the Earth, that is, makes a translation around our planet and carries out a rotation on its own axis. Both processes, unlike what happens with the Earth, have a matching period of 28 days, by which our satellite ends always displaying the same face in the skies of our world.
Accordingly, emphasis on the importance of the land by its unique status in the solar system, such as celestial body habitable by all known life forms and, in particular, the human race. Given the concrete impossibility that we currently have to "terraform" (make similar to Earth) to other planets or satellites, it is essential to preserve the planet in a responsible and systematic manner.

Article contributed by the team of collaborators.