The earth It is the third planet in the solar system (taking into account its distance from the sun, 150 million kilometers) and although it was formed at the same time as the sun and the rest of the system that houses it, it has been 4,570 million years, is in the the only planet on which until now it has been proven that there is life.
After successive polemics, dimes and diretes and some more complicated issues that occurred at some moments in history (Middle Ages), such as persecutions against those who held a different position or vision of the established order, precisely in historical periods in which was not frowned upon, it was concluded that the shape of the Earth is geoid, similar to a sphere but flattened. In this way, what the first cultures maintained about the format of the planet as "flat Earth" was discarded, giving the right to several astronomers and ancient philosophers such as Plato and Aristotle, who thought 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. Likewise, many non-European civilizations, such as the cultures of Mesoamerica and some peoples of Asia, speculated on the sphericity of the Earth already in ancient times. However, in the 16th century this hypothesis could only be demonstrated thanks to the voyage around the world that Juan Sebastián Elcano undertook by boat, as the surviving captain of the voyage initiated by Magellan.
Among the 8 planets currently considered in the solar system, Earth is defined as the largest of the solid planets, with an equatorial diameter of 12,756 km, thus surpassing Venus, Mars and Mercury, in that order of volume. Likewise, it is the only one that has a single natural satellite (the Moon), since the remaining planets either have at least 2 moons (such as Mars) or lack satellites, as occurs with Mercury or Venus. It is worth remembering that Pluto is not currently considered a planet, but rather an intermediate level celestial body (plutoid or dwarf planet).
The Earth is composed of four great zones or layers: the lithosphere, the hydrosphere, the atmosphere and the biosphere; meanwhile, it is the only planet that has 71% of its surface covered by water. This situation is what explains the bluish color and also undoubtedly the one that has allowed the development and survival of the living species that populate it. Another peculiarity is the homeostasis capacity that it presents and that thanks to this property it can recover from the worst natural disasters in a very short term. Likewise, it is the only celestial body in the solar system in whose atmosphere a predominance of nitrogen and oxygen is described, which is ideal for the growth and development of living beings.
And regarding its movements, studies have shown that the earth has at least two movements: that of translation, which is the movement around the sun, and that of rotation, which consists of a change of orientation. The translation phenomenon is carried out on an elliptical orbit and takes a total of approximately 365 days, thus giving rise to a calendar year and the 4 seasons as we know them. On the other hand, the rotation process is the rotation of the planet on a hypothetical axis, which is completed in an approximate period of 24 hours and is considered responsible for the sequence of day and night. It is highlighted that the Moon performs homologous movements in relation to the Earth, that is, it 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 coincident duration of 28 days, which is why our satellite always ends up exhibiting the same face in the skies of our world.
Consequently, the importance of the Earth is emphasized due to its unique condition in the solar system, as a celestial body inhabitable by all known forms of life and, especially, by the human race. Given the specific impossibility that we currently have to "terraform" (make Earth-like) other planets or satellites, it is essential to preserve the planet in a responsible and systematic way.
