The Importance Of The Study Of Thermodynamics

The universe is fundamentally controlled by cause and effect. Everything has a cause, and everything has an effect. Within this regime, everything requires energy, releases energy, or most often, both. Thus, the study of transferring energy is paramount to understanding the universe. Much of the energy we observe, and rely on, as humans is thermal energy from the sun. Therefore, Thermodynamics is very important.

Without Thermodynamics, we can not understand why simply can not have an understanding of the world around us. Thermodynamics is the basis of metamorphic petrology, or the study of rocks that have been deforemed by heat and pressure. Earth has four major distinct layers: A thin rocky crust, a thick solid mantle that deforms plastically, a liquid iron outer core, and a solid iron inner core. The mantle, which represents approximately 84% of earth volume, is completely composed of metamorphic rocks, and thus is only understood through thermodynamics. It is impossible to directly observe the mantle, due to the high heat and pressure. Thus, our understanding of the mantle is based mostly off thermodynamic predictions. Using the chemical composition of exposed, but altered sections (namely mid-ocean spreading ridges), and controlled pressure-temperature experiments we can predict the mineral phases of the mantle. This reveals that the mantle is a solid green material. This non-obvious result is only realized through thermodynamics. This is why thermodynamics is important. It allows use, as geochemists, to make predictions about the earth that we can not directly observe. This is true on the huge scale of understanding the mantle, but also on much smaller scales. In 2007, Nishiyama M. Enami and his research group began using Raman spectroscopy on quartz-in-garnet inclusions to predict pressure and temperature of the peak conditions of the host rock.

The method relies on the fact that quartz (SiO2) is highly deformable, however, garnet (X3Y2(SiO4)3) is not. Thus, even when the extreme pressure of deep metamorphism is relieved, the quartz embedded in garnet crystals preserve the deformation experienced at high pressure. This type of study helps solidify understanding of high P-T processes, that are otherwise difficult to probe. Undoubtable, the use of thermobarometry in geochemistry originated with the Norweigen mineralogist, Victor Goldschmidt. He revolutionized the field by applying physical chemistry, and thermodynamics to geological problems. Likely, he is most famous for contact metamorphism in a Southern Norway. Here, he discovered that some mineral assemblages were mutually exclusive. For instance, andalusite can be associated with cordierite, but never with orthopyroxene. With this development, Goldschmidt realized that mineral phases were dictated by temperature and pressure, and thus could be indicative of conditions in the inner earth. Now, based on Goldschmidt’s work, we can plot paths through pressure-temperature space of a host rock by way of the mineral assemblage, and our understanding of thermodynamics. However, the use of thermodynamics to understand deep earth processes is not over. The earth has two chemically distinct forms of crust: continental crust and oceanic crust. All rocky bodies we have ever observed have only one type of crust, making earth fundamentally different. Bradley Hacker purposes the solution is based on thermodynamics. He asserts that over the geological time scale, continental crust as differentiated due to subduction. A thin veneer of sediments is subducted on the downgoing oceanic plate, which due to its low thermal diffusivity, remains cold and is allowed to buoyantly rise, and “relaminate” to the base of the overriding plate. However, this begs the question, “Why do other planets not have subduction?” The answer here lies in our mantle. The convection of our solid mantle is still debated, and is fundamentally an issue of thermodynamics. Issues, such as the rate of surface heat dissipation, mantle plumes, large igneous provinces appear contrary to our understanding mantle convection, and thus of thermodynamics in the earth as a whole. The field of geology is as old as human’s need to understand the world around us. The use of thermodynamics to understand geology is similarly as old as the work by Boyle, Gay-Lussac, Maxwell, and others.

However, quantitative analysis of geological samples has been hindered by technology, and has only become accepted with the advent of high-precision mass spectrometry. Thermodynamics is fundamental for our understanding of the earth. From understanding the physical composition of the earth to being able to answer simple questions about a small suite of rocks, thermodynamics provides the basis of our understanding of metamorphic terranes, and thus the majority of the solid earth. There is still much to learn about earth, and thermodynamics is fundamental in answering the questions earth raises. This is why the study of thermodynamics is important.