This is the surface shell that we have become more familiar with, even if its true nature has only emerged in recent years thanks to artificial satellites in orbit around the Earth, which with their "electronic" eyes can scan even the most remote and inaccessible parts of the planet that are hidden from man. Curiously, the most evident features of the planet are not the mountains, which to us seem to be so high and majestic. Even Everest, the highest point on the planet, represents a variation of the Earth's radius of just slightly more than a thousandth part: a little more than a wrinkle in the enormous Asiatic continent if seen from space. Instead, the giant frozen caps which cover the poles stand out quite clearly because they are only rarely covered by clouds and in reality are some of the most arid regions on the planet. Especially in Antarctica, the air is too cold and the continent too large to be affected by the moisture of the surrounding oceans. But then how come there is so much ice? The fact of the matter is that, no matter how little snow falls each year, it never melts and thus remains frozen forever on the continent. In addition, about 600 000 years ago, conditions on the Earth became just right for an exceptional expansion of the ice in the south and in the north, where it even covered a large part of Europe, all of Canada and a part of the United States: the glacial ice caps are the remains of that gigantic white mass. Another evident feature is the mass of water in lakes, rivers, which wind through the heart of the continents bringing them life, and the islands which stud the seas and oceans like jewels. On the continents, the vast expanses of deserts alternate with forests and cultivated areas. And the cities, our homes, are nothing but small, dark and almost invisible areas in the land that surrounds us. Here and there, the expert eye of geologists can identify what remains of the ancient bombardment of meteorites that struck the Earth just after its birth: they are large and small craters that the erosion by the wind and rain has almost wiped out or which have been filled with water and transformed into lakes. We have discovered about eighty of them, with diameters ranging from 100 meters to 100 kilometers: one of the most famous is the Barrington Crater, in Arizona, which has remained almost completely intact thanks to the desert-like environment where it is located and the fact that the meteorite that produced it fell on the Earth in very recent times from a geological point of view: only 20 000 years ago.
This is the surface shell that we have become more familiar with, even if its true nature has only emerged in recent years thanks to artificial satellites in orbit around the Earth, which with their "electronic" eyes can scan even the most remote and inaccessible parts of the planet that are hidden from man. Curiously, the most evident features of the planet are not the mountains, which to us seem to be so high and majestic. Even Everest, the highest point on the planet, represents a variation of the Earth's radius of just slightly more than a thousandth part: a little more than a wrinkle in the enormous Asiatic continent if seen from space. Instead, the giant frozen caps which cover the poles stand out quite clearly because they are only rarely covered by clouds and in reality are some of the most arid regions on the planet. Especially in Antarctica, the air is too cold and the continent too large to be affected by the moisture of the surrounding oceans. But then how come there is so much ice? The fact of the matter is that, no matter how little snow falls each year, it never melts and thus remains frozen forever on the continent. In addition, about 600 000 years ago, conditions on the Earth became just right for an exceptional expansion of the ice in the south and in the north, where it even covered a large part of Europe, all of Canada and a part of the United States: the glacial ice caps are the remains of that gigantic white mass. Another evident feature is the mass of water in lakes, rivers, which wind through the heart of the continents bringing them life, and the islands which stud the seas and oceans like jewels. On the continents, the vast expanses of deserts alternate with forests and cultivated areas. And the cities, our homes, are nothing but small, dark and almost invisible areas in the land that surrounds us. Here and there, the expert eye of geologists can identify what remains of the ancient bombardment of meteorites that struck the Earth just after its birth: they are large and small craters that the erosion by the wind and rain has almost wiped out or which have been filled with water and transformed into lakes. We have discovered about eighty of them, with diameters ranging from 100 meters to 100 kilometers: one of the most famous is the Barrington Crater, in Arizona, which has remained almost completely intact thanks to the desert-like environment where it is located and the fact that the meteorite that produced it fell on the Earth in very recent times from a geological point of view: only 20 000 years ago.
