If five years ago I was asked about how I think the city of the future, then certainly I would say that this city, where instead of buses, trams and trolley buses carrying passengers spaceships and people run the factories, mills, a fully automated and subordinate to computer programs. The children in this town do not know no worries: at their disposal the best toys, rides, computer games ...
But the years pass, we get older and realize that children's dreams - it's just fantasy.
The city of my dreams - a modern metropolis with a lively, neat, comfortable houses in which there is heat and electricity, in which no water and sewer breaks, forming a fetid rivers and lakes, which are working elevators, and entrances are like showrooms.
It was not until the time of Copernicus (the sixteenth century) that it was understood that the Earth is just another planet.
Mir and Earth's limb
Mir space station and Earth's limb
Earth, of course, can be studied without the aid of spacecraft. Nevertheless it was not until the twentieth century that we had maps of the entire planet. Pictures of the planet taken from space are of considerable importance; for example, they are an enormous help in weather prediction and especially in tracking and predicting hurricanes. And they are extraordinarily beautiful. The crust varies considerably in thickness, it is thinner under the oceans, thicker under the continents. The inner core and crust are solid; the outer core and mantle layers are plastic or semi-fluid. The various layers are separated by discontinuities which are evident in seismic data; the best known of these is the Mohorovicic discontinuity between the crust and upper mantle. The core is probably composed mostly of iron (or nickel/iron) though it is possible that some lighter elements may be present, too. Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. The lower mantle is probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium and aluminum. We know most of this only from seismic techniques; samples from the upper mantle arrive at the surface as lava from volcanoes but the majority of the Earth is inaccessible. The crust is primarily quartz (silicon dioxide) and other silicates like feldspar.