A blue globe, flanked by a smaller and darker body, brilliantly stands out against the blackness of space: thirteen days after its departure, this is what the automatic probe Voyager 1 sees when it looks back and photographs the Earth-Moon system for the first time, as it heads towards Jupiter and the other outer planets. But as we approach the Earth after leaving the inhospitable Venus, we begin to make out those details that make this the most unique planet in our solar system: vast expanses of water with the brown masses of the continents peeking out from under the white streaks of clouds. This is our "home", an evolving world that is continuously changing, sometimes violently by volcanoes and earthquakes and sometimes imperceptibly by the erosion of the atmosphere and water. A world in which the vegetation changes color with the passing of the seasons, and is covered with snow or flowers. A world that was not always thus, but one which was tremendously transformed over the 4 600 000 000 years since it was created. When the first particles of matter of the primordial nebula began to condense, a larger and larger "ball" began to form in the position of the third planet. Then, inside the Earth that had already been heated by the continuous collisions with smaller bodies, the temperature increased even more because of radioactive substances and even went as high as 2 000 degrees Celsius. At this point, our planet was a kind of boiling pudding in which the heavier materials, like iron, began to "sink" towards the center where they formed a superdense core. Instead, the lighter materials floated to the surface and soon began to cool, forming the crust. It is during this last phase, which occurred around four billion years ago, that the fragments still in orbit or wandering through the solar system began to fall on the newly formed surface, studding it with craters of all shapes and sizes. This phase, which is common to all planets, lasts about 500 000 000 years; then the number of impacts decreases and the history of each world takes a different path.
A blue globe, flanked by a smaller and darker body, brilliantly stands out against the blackness of space: thirteen days after its departure, this is what the automatic probe Voyager 1 sees when it looks back and photographs the Earth-Moon system for the first time, as it heads towards Jupiter and the other outer planets. But as we approach the Earth after leaving the inhospitable Venus, we begin to make out those details that make this the most unique planet in our solar system: vast expanses of water with the brown masses of the continents peeking out from under the white streaks of clouds. This is our "home", an evolving world that is continuously changing, sometimes violently by volcanoes and earthquakes and sometimes imperceptibly by the erosion of the atmosphere and water. A world in which the vegetation changes color with the passing of the seasons, and is covered with snow or flowers. A world that was not always thus, but one which was tremendously transformed over the 4 600 000 000 years since it was created. When the first particles of matter of the primordial nebula began to condense, a larger and larger "ball" began to form in the position of the third planet. Then, inside the Earth that had already been heated by the continuous collisions with smaller bodies, the temperature increased even more because of radioactive substances and even went as high as 2 000 degrees Celsius. At this point, our planet was a kind of boiling pudding in which the heavier materials, like iron, began to "sink" towards the center where they formed a superdense core. Instead, the lighter materials floated to the surface and soon began to cool, forming the crust. It is during this last phase, which occurred around four billion years ago, that the fragments still in orbit or wandering through the solar system began to fall on the newly formed surface, studding it with craters of all shapes and sizes. This phase, which is common to all planets, lasts about 500 000 000 years; then the number of impacts decreases and the history of each world takes a different path.
