Weathering of rocks
In the literature of geography, the mechanism of weathering (1) has generally been distinguished into two types: mechanical and chemical. These two mechanisms do in fact occur parallel with one another and reinforce each other. To make things more clear, we can use the tea and sugar example. When we press a sugar cube in our hand, it becomes powdery, in other words it becomes weathered. Mechanical weathering occurs in a similar way too. A boulder breaks into parts, small and big, during the tumbling process and the rain water which penetrates into their fractures becomes iced due to the cool weather which causes further cracks on their surfaces. And as the weather becomes warmer over time, more fractures occur on the rock pieces due to the increased effects of the melted ice on those cracks and cavities. This mechanism is more apparent on high mountains because here the weather temperature decreases at a rate of 0.5°C every 100 meters.
Salt is another substance which causes enlargement of rock fractures. Salt plays a crucial role on rocks especially at arid regions and on shorelines. Due to hot weather, salty water inside the fractures evaporates and salt crystals remain as evaporation residue. With the frequent occurrence of such evaporation, salt crystals become larger and larger and rock fragments eventually break off. Roots of growing plants may also weaken the structure of stones and rocks.
Small scale mechanical weathering is also linked to large scale erosion. Large volumes of rock masses weathered by erosion may be transferred to other places by means of water, wind and ice displacement. Also, large and small fractures of rocks may occur on land, mountains and slopes during such displacements due to excessive collision and friction of rocks. Cracks and fractures that occur through the means of various mechanisms provide larger areas for chemical weathering. Owing to this and also under the influence of living creatures and particularly water, mineral properties of rocks undergo changes and eventually dissolve. The dissolving nature and functioning of water is highly important since dissolution, oxidization and hydrolysis constitute the main process of chemical weathering. Chemical weathering is quite similar to the melting of sugar inside tea by way of its mechanical stirring with a spoon and under the influence of hot water. Rocks, too, are mechanically exposed to the same condition as easily as that of powder sugar within tea. However, weathering of a huge rock occurs over a longer period of time as compared to that of a sugar cube.
The resolving power and capacity of water increases when a small amount of acid—coming, for instance, from plants or animals ready to decompose—is added into it and certain minerals that are difficult to break down such as calcium-carbonate dissolve in it much easily. Water also ensures oxidization and hydrolysis, and of minerals to undergo change.
Since the creation of the world, stones and rocks on the earth’s surface have all been under the influence of this constant mechanical and chemical weathering mechanism, and it seems that—pursuant to the cause and effect principle—such a mechanism will continue until the doomsday. While these two weathering mechanisms reinforce one another, they sometimes occur independently of each other. The weathering process to which rocks are subjected causes them to undergo chemical and physical changes in their mineral properties under the influences of air, heat, and living creatures. Different minerals which constitute rocks may thus be easily dissolved.
The rocks we see as cold and lifeless indeed form the foundation of the earth and is the main source which nourishes all living creatures. If such a perfect mechanism of weathering did not exist, the soil—which is the ideal source of sustenance on earth in context of the cause and effect principle—would not have come into existence, for the weathered rocks constitute the raw material of the soil. Plants absorb necessary amounts of minerals such as calcium and magnesium through their roots which is transferred from rocks into the soil. The minerals that make up the rocks pass from the rock to the soil, from the soil to the plants and from plants to animals. Then finally, from plants and animals they are put at the disposal and to the benefit of human beings.
The resemblances between rocks and the human body are noteworthy. Many minerals like calcium which are found in limestone and soil are also found in the human body. Calcium is the basic ingredient found in the bones and teeth of human beings and other vertebrates. Likewise, cobalt which is also found in rocks plays a role in the increase of red blood cells and cell division and also takes part in the composition of vitamin B12 which plays an important role in human neural system.
In conclusion, the weathering mechanism which has been continuing since the creation of the earth up until now might not have been seen as an important event at first sight. However, this mechanism constitutes the basis of worldly life as far as the cause and effect rule is concerned. Minerals that constitute rocks and mountains are, by the grace of God, being weathered and so being put at the disposal and to the benefit of all human beings and all living creatures. Isn’t this a clear manifestation of the All-Merciful One for those who ponder and meditate?
Yusuf Goker is a freelance writer in the field of geology. He lives in Turkey.