Planet Earth consists of 3 main layers
The crust is the outermost layer of the planet, consisting of rocks, often basalt and granite. These rocks form the ocean crust, which consists mainly of basalt, and the crust of the continents, which consists mainly of granite.
The mantle or curtain layer, which is the layer directly next to the crust, and its thickness reaches approximately 2900 km, and it consists of molten and dense rocks rich in iron and magnesium, and where the upper layer of it, along with the crust layer, is what is called the lithosphere, which is divided into tectonic plates, some large and others smaller. Its movements contribute to the occurrence of earthquakes, floods, and volcanic eruptions, which contribute to changing the shape of the outer crust and the emergence or collapse of natural features.
The core The core consists mainly of two layers, a molten outer layer, and a solid inner layer, both of which are composed of nickel and iron, and the temperature in it may reach 50,000 degrees Celsius.
Underground Cities There are many ancient and archaeological tunnels located in different places of the globe, we mention some of them as follows
The city of Cappadocia, which is located in Turkey, is home to no less than 36 underground cities, at depths of approximately 85 m. Derinkuyu is the deepest, as it was discovered in 1963 AD and contains all the landmarks and facilities that indicate that it is a city similar to the usual cities above the ground. Such as: residential quarters, stables, temples, warehouses, factories, and others. It is rumored to have been home to more than 20,000 residents.
Vialichka salt mine,
Where this mine was built in the thirteenth century, and the salt extracted from it continued to be manufactured until 2007 AD, and it is one of the most important tourist attractions in Poland, since before it was a mine it was a series of caves filled with salt and made up a maze that currently adorns more than 185 miles Of the distinguished exhibitions, approximately 3,000 rooms, and 9 floors, but only the first 3 floors are available for visits
The city of Dixia Cheng was built in 1970 AD to be a shelter and shelter for citizens in the event of any storming, explosions, or nuclear attack, and throughout this city, which is referred to as the Great Wall located underground, there are approximately 100 different entrances, and it was built to contain everything the city needs To be livable, such as: schools, hospitals, and places to sleep, especially in the event that citizens need to stay in these shelters for a long time.
