All large deserts are located near the 30th degree of both southern and northern latitudes. This condition did not come about by accident. Any wind blows from a less heated surface to a more heated one. The trade wind winds blowing from 30 latitudes to the equator are no exception. In the center, the north trade wind meets the south one and, under their counter pressure, the air begins to rise to the top. Considering that the paths of the trade winds for the most part lie over the oceans, where they absorb evaporating moisture, then all this steam will begin to accumulate over the equator. In the end, clouds thicken over the region and heavy rain falls on the ground, returning all the water accumulated by the winds back.
From this moment, the empty air masses, which have become dry, are pushed out by the new ascending air towards the poles. This air flow is called the antitrade wind. By 30 latitudes, dry air will begin to sink, heating up by one degree every 100 meters down and becoming even drier. There is no moisture in such air, it does not carry clouds with it, and therefore it almost never rains here. Such air circulation developed hundreds of thousands of years ago, which led to the complete drying of the earth during this time. Deserts have formed.
The thickness of the sands is not a constant value. In each region, the figures differ and change depending on the territorial winds and the movement of sand dunes. However, it is known that the average thickness of the sands of the Sahara Desert is 150 meters, the Gobi Desert - 200 meters, the Libyan Desert - 300 meters, the Namib Desert - from 200 to 400 meters. Directly under the sands is a stone surface. In addition, the bowels under the sands are fraught with huge deposits of various resources. In the same Sahara, at a depth of 150 to 500 meters, the world's largest artesian pool of water was discovered. The bowels of the Namib desert are rich in deposits of diamonds, tungsten and uranium ores, the Arabian sands are rich in oil and gas, etc.