How should we understand the verses that state that the heavens and the earth are of seven layers?
Allah is He Who created seven Firmaments and of the earth a similar number, through the midst of them (all) descends his Command " (Al-Talaq, 12).
First we should say that since the numbers like seven, seventy and seven hundred are used to describe plentitude in Arabic, seven layers may indicate the plentitude of those layers
As a matter of fact it is possible to deduce different meanings from this expression in the verse. As far as it is understood today space is not an endless vacuum but it is full of a substance called aether.
Layers like water, vapor and ice form from hydrogen and oxygen. Similarly, the Almighty Glorious arranged the seven layers of the heavens from the substance aether in a very fine system and created the stars in it. The moving stars travel in the heavens like the fish.
It is possible to infer from this verse that all of the visible heavens form one sky of this world and that there are six more layers of sky. The expression about the earth may also indicate different meanings. However, here we will deal with only one aspect of the expressions about both the heavens and the earth, that is, the apparent meaning.
It has been proved that the heavens and the earth consist of seven different layers by astronomy and geology.
Lets examine the seven-layer world with a radius of 6370 km beginning from its crust towards the core. (1) This structure consists of the following seven layers from outside to inside:
1- (Lithosphere or Crust)
3- (Upper Mantle, Astenosphere)
4- (Transition Zone)
5- (Lower Mantle, Mesosphere)
6- (Outer core)
7- (Inner core)
1- Lithosphere or Crust
The crust which is also known as the lithosphere is located in the outermost part of the earth. The average thickness of the crust is about 33 km; it is thicker under the land (35-40 km, under the Tibetan Plateau 70 km) and thinner on the ocean base (8-12 km). It consists of two parts with different chemical composition and density. One of them is the granitic crust that consists of rocks in granite composition; the other is the basaltic crust that consists of rocks in basaltic composition.
The elements silicon and aluminum are dominant in the granitic crust. Therefore it is lighter; its density is between2.7-2.8 gr/cm3. It forms the upper layer of the earths crust. Structures containing silicon and magnesium are dominant in the basaltic crust. Therefore it is heavier than the granitic crust; its density varies between 3 and 3.5 gr/cm3. It lies under the granitic layer and on the oceanic base. Therefore the basaltic crust is sometimes called the oceanic crust. (2)
The seas, lakes, rivers and underground waters on the earth form the hydrosphere. ¾ of the earths surface is covered with water. (3)
The mantle consists of three different layers; upper mantle, transition zone and lower mantle. It forms 83% of the worlds volume and 66% of the worlds weight.
3- The thickness of the upper mantle is 360 km and the density is between 3.3 and 4.3 gr/cm3.
4- The transition zone lies between the upper mantle and the lower mantle. It is 600 km thick.
5- The lower mantle consists of denser and more elastic rocks. It is 1900 km thick.
The core forms the part of the earth from 2900 km to 6370 km. It is divided into two as the outer core and the inner core.
6- The Outer Core: It forms the part between the 2900 th km and 5150th km. The main substance of the outer core is molten iron and nickel. Since the secondary (S) waves of the earthquake waves cannot pass through the outer core, this part is understood to be in a liquid form. Secondary waves cannot pass through liquids.
7- The Inner Core: The density reaches to 12.3 gr/cm3 and the temperature to 4300 degrees in the boundary of the outer and inner cores. The composition of the inner core consists of crystallized iron and nickel. As it is known, the earth on which we live has the property of a giant magnet. Its magnetic field emanates from the arrangement of its liquid outer core as a dynamo. Thanks to this property the compass needles always orientate towards the same point. (4)
"He Who created the seven heavens one above another; no want of proportion wilt thou see in the Creation of (Allah) Most Gracious. So turn thy vision again: Seest thou any flaw?" (Mulk, 3).
We live under the atmosphere; just as the fish living in the sea. Before we soar to the upper parts of the sea of air, lets know about the general characteristics of the atmosphere.
The atmosphere consists of 78 % nitrogen, 21 % oxygen and very little argon, carbon dioxide, hydrogen and other rare gases. If this rate were not maintaned, life on the earth would not be possible. The atmosphere also functions as an umbrella that protects the living things in the world from harmful radiations. For instance, the atmosphere filters the ultraviolet rays from the sun. If it did not filter them, these rays would kill all of the living things. If the atmosphere did not exist, the temperature in the world would be over 100° C during the day and it would be freezing during the night. It shows that the atmosphere also regulates the heat energy.
One of the most important aspects of the atmosphere is that it carries the rain clouds to the areas where they are needed.
The atmosphere is a great blessing of Allah that has the most indispensable substances like nitrogen, oxygen and carbon dioxide. Just suppose that there was no oxygen, would the smallest units of our body, the cells, function? Without oxygen we would not be able to burn what we eat and get the necessary chemical energy. Thanks to oxygen the burning called oxidation takes place in the cells and the molecules that form the food undergo chemical changes.
It is very difficult to say something about the thickness of the atmosphere. The weight of 1 mil cube of air in the sea level is 6 million tons. 350 km up, the weight of the air with the same volume is 60 grams. As it can be understood from this example the density of the air decreases as we go up. About 130-140 km up, since there are not enough moving air molecules, sound waves cannot be transmitted and as a result it is not possible to hear even the sound of a hammer.
The layers that form the atmosphere and the space(*):
1- Troposphere: The lowest layer of the atmosphere in which we live is called the troposphere. The troposphere varies in terms of temperature and humidity rate depending on the regions. Its thickness changes between 0 and 16 kilometers.
2- Stratosphere: It forms the second important layer of the atmosphere and lies over the troposphere. It lies between 11th and 50th kilometers. Most of the military planes travel in this layer. The temperature is about fifty-five degrees under zero (-55°C). There are no winds in the stratosphere and consequently no clouds.
3- Chemosphere: It reaches to an altitude of 80 km and lies over the stratosphere. Gas molecules are transferred into atomic gas or vice versa here.
4- Mesosphere: It forms the middle part of the atmosphere.
5- Ionosphere: It reaches to 400 km over mesosphere. The air is charged with electricity in this layer because the atoms of the gases that form the air have lost or won electrons. This layer is called the ionosphere because it contains electrically charged atoms, namely electrons.
The ionosphere reflects the electrically charged particles and radio waves. Otherwise how would we hear the broadcast of the radio station at other end of the world? Thanks to this property we can easily listen to the radio broadcasts of overseas countries on the short wave. As for the waves of television transmitters; they cannot be reflected here, they pass through this layer.
6- Exosphere: It is the layer over the ionosphere where the density of the air decreases a lot. Since the density of the air is very low, friction is very little and negligible. Therefore the artificial satellites constructed by human beings rotate around the world in this layer.
7- Magnetosphere: It fills the eternity of the space. It is a vast endless place where there is no atmosphere, that is, air. It partly contains the exosphere too and covers the space beyond 64 000 km.
As it can be understood from this short explanation, the Quran indicates the outmost boundary of the sciences and encourages the human beings to search the wisdom, art and system in the works of Allah. Naturally these encouragements and indications are in a way that is appropriate to the understanding and realization of the human beings in all ages and open to various interpretations.