Cracking Earth's Layers
The inner core, outer core, mantle and crust: the phrase we frequently hear when discussing the layers of the earth and it comes so easily to us that we simply don’t question it. Yet, this topic is extremely complex and has great implications for understanding our world. Hence the methodology, like any other scientific discipline, requires the use of many perspectives to develop our understanding of this topic. For the purpose of this essay, the discussion will focus on outlining the main methods used to research the layers of the earth.
Firstly, the most obvious method of obtaining evidence - drilling. It sounds quite self-explanatory to dig below the surface of the earth to directly analyse the layers; however, the process is slightly more complex. Due to the incredulous temperature and pressure inside, the equipment required to withstand these conditions is beyond our engineering capabilities and the force required to penetrate through the molten layers of the earth is immense. Even so, there have been attempts in the past to achieve just this. In the 1970s, The Kola Superdeep Borehole project conducted by the Soviets dug a hole with a depth of 12,262 metres, which was discontinued because the temperature was higher than expected. This was the deepest humankind has ever dug, even so, it barely scratched the surface of the crust. In 2003, David Stevenson, an astronomer from the California Institute of Technology in Pasadena suggested a method that could potentially achieve this. Stevenson proposed to open the earth’s surface with several megatonnes of TNT which will create an earthquake of 7 on the Richter scale, followed by pouring thousands of tones of molten iron and geological instruments to collect the data. This method is very extreme and luckily, it was purely proposed to illustrate the difficulties of directly investigating the layers of the earth. The Kola Superdeep Borehole project was our best attempt using a direct approach and although it failed, it provided some data regarding temperature and the types of matter which is in the earth’s crust. The most important thing to take from this project is the difficulties of directly researching the layers of the earth, which is why indirect methods are used instead.
The indirect method that will be discussed is to use chemical analysis to study the elemental compositions of rocks using diamonds. It is known that diamonds have a giant covalent lattice structure hence can tolerate high pressures, and temperature, and is chemically inert. Moreover, diamonds contain impurities contained within minerals, called inclusions, which preserve materials inside the matrix of the diamond. These characteristics make diamonds one of the most important vessels used to study the various elemental compositions of matter at different depths. Diamonds used to study this can be found at different depths with inclusions, which is demonstrated in the image below: a diamond used found shallower is a lithospheric diamond (found at depths between 120 to 220km) and super deep diamonds (between 700-800km). When these rocks are extracted, geochemical instruments, such as mass spectrometers, x-ray crystallography, and micro-imaging techniques are used to analyze the elemental composition of the inclusions. This deduction provides implications for the range of elements that exist within the layers of the earth, which can develop our understanding of how this affects the characteristics of each layer.
The last and final method for discussion is the use of seismology, the study of seismic waves. These waves are vibrations of energy caused by the movement of the material inside the earth, which is commonly associated with earthquakes. This geophysical study can help provide us with data about the insides of the earth by relying on the properties of waves. The density of matter affects the speed that the waves travel through, which can be used to ascertain the properties of the material that the layers are composed of. The two types of seismic waves that are used are pressure (P) waves and shear (S) waves: P waves can travel quickly through liquids and solids, while S waves are slow and can only travel through solids. This property is demonstrated in the image beside, which outlines how these waves interact with each layer of the earth. By knowing the speed at which these waves travel through the layers, scientists can deduce the distance of each boundary, as well as the state of matter each layer is composed of.
With all this effort to deduce the layers of the earth, the table below summarizes the physical and chemical characteristics of each layer.
By using the methods mentioned previously - including but not exclusively drilling, analyzing diamonds, and studying seismic waves, scientists are closer to understanding the mechanics and the composition of the layers within the earth. This subject is often overlooked as it seems simple and not worthy of study, yet in reality, studying the inside of the earth provides extremely significant and impactful implications in science. In the near future, new technologies and methods will arise and be used to lead us closer to understanding our dynamic planet and the universe we live in.
By Gao Kamalanavin
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