Our planet is very peculiar in many aspects. It has a concentric structure formed by layers that encompass others and are in different states.
From the inside out, part of the core is in a molten state surrounded by the geosphere, formed by different rock layers. Above them is the hydrosphere, composed of all the liquid water on the planet. Above this is the atmosphere formed by different gaseous layers.
As regards the geosphere, our planet is currently the only one in the Solar System that continues to present an active plate tectonics. Venus and Mars seem to have had it in their day, but it has now been ruled out. This active tectonics is responsible, among other things, for erasing the impact craters of meteorites from the surface, as well as altering the distribution of seas and oceans.
In the classification of planets, Earth is considered a rocky planet, since it has different layers in its internal structure (core, mantle and crust), unlike the so-called gas planets. Visit the page on Layers of the Earth If you want to know more details about the matter.
Applying Newton's laws - universal gravitation and gravitational acceleration -, the mass of planet Earth is considered to be 5.98 x 1024 Kg, while it has a density of 5.52 gr / cm3. That is, it is the densest planet of all of the Solar System. This is because it has abundant amounts of heavy elements such as Si, Ca, Mg, O, Fe or Al, which combine with each other forming stable structures in the rock-forming minerals.
However, and since the planet has different layers of different composition, it would not be appropriate to say that the rocky or solid part of the planet (geosphere) has an average density of 5.52 gr / cm3, since none of its layers has such value. In fact, from the surface to the core of the planet the density is increasing, so that the crust has an average density of 2.7 gr / cm3, the mantle of 4-6 gr / cm3 and the inner core of up to 11 g / cm3.
The Earth, like Venus or Mars, has an atmosphere that makes the surface have an average temperature of 15 ºC, so that the water is in its three states (solid, liquid and gas).
As if all this were not enough, the Earth has a very intense and bipolar magnetism, which is believed due to the movement of electrified charges inside the planet, specifically in the Earth's core.
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