Thermodynamic System of Planet Earth PART-1

Life and Earth System:

It is now universally acknowledged that life has had a significant impact on the Earth's system. Vernadsky established this idea – that life is the geological force – in his landmark work "The Biosphere" many years ago. Lovelock gave a specific example of such an effect, the changing of atmospheric composition by life, concerning the exceptionally high concentration of molecular oxygen in the Earth's atmosphere, nearly four decades ago. When compared to other planetary atmospheres in the solar system, this state represents chemical disequilibrium concerning other constituents of the atmosphere. Photosynthetic activity, which accounts for the majority of life on Earth, is directly tied to the creation of molecular oxygen. Photosynthetic activity harnesses the power of sunlight to convert carbon dioxide and water into chemical-free energy in the form of carbohydrate and molecular oxygen, which is then released into the atmosphere. If photosynthesis did not supply oxygen regularly, it would react, and the atmospheric composition would achieve a state of thermodynamic equilibrium. According to Lovelock, the observed disequilibrium in the atmospheric composition is related to the presence of life, and so is an undeniable indicator of a planet with widespread life.

Disequilibrium can be detected concerning are a variety of other variables, not just atmospheric composition. For example, over time, a redox gradient evolved between the oxidizing atmosphere of the Earth and the reducing crust, which is depleted by geological reactions. From the mountain peaks to the seafloor, topographic gradients form, which are continuously eroded by erosion and sediment transport. How do these gradients stay in place? Is life involved in the maintenance of these situations of disequilibrium?

To establish a holistic theory of life in the Earth system, Axel Kleidon extends Lovelock's perspective of thermodynamic disequilibrium and life to processes of the entire Earth system as well as their interactions. Axel Kleidon accomplishes this by expressing Earth system processes in general thermodynamic terms. This will enable us to calculate disequilibrium with a larger number of variables and comprehend the driving forces behind such states. The effect of life on the driving forces of planetary disequilibrium states can then be quantified using such a hypothesis. Interactions, as well as thermodynamics, play a key role in this theory, as we'll discover.

Importance of biosphere-atmosphere–geosphere interactions:

Organisms can create long-lasting structures using the chemical-free energy supplied by photosynthesis. Leaves, stems, and roots, for example, are constructed by plants. These long-lasting structures improve the ability of trees to absorb solar energy and, on land, allow them to reach water deep in the soil. As a result, organisms have an impact on the amount of incoming solar radiation received and the pace at which precipitated water is evaporated back into the atmosphere, both of which have an impact on the surrounding environmental conditions. Furthermore, these two examples influence not only the photochemical machinery of organisms (e.g., leaf temperature via latent heat of water) but also the overall environment (in terms of water vapour concentration in the atmosphere).

In the presence of terrestrial plants, only these two physical impacts – higher solar radiation absorption at the surface and enhanced ability to recycle water to the atmosphere – can significantly alter physical environmental conditions. On a local scale, these contrasts can be sensed when comparing the cool, moist air of a forest to the scorching, dry conditions of a parking lot on a hot summer day. These effects modulate temperature and continental moisture recycling at larger scales, as shown by extreme climate model simulations of a "green planet" – a world where rainforests were planted everywhere on land – and a "desert world" – a world where the effects of terrestrial vegetation were removed. When these different physical conditions are compared in terms of what they mean for biotic activity, it is discovered that the conditions of the "green planet", as well as the present-day, allow for significantly better output. In evolutionary terms, such self-enhancing effects could be explained as a result of "feedback on growth."

Life modifies the chemical environment on Earth, resulting in biogeochemical impacts and feedbacks, in addition to these physical effects. Life impacts the strength of the greenhouse effect and thus surface heating by changing the chemical composition of the atmosphere. Life has significantly impacted the weathering rates of silicate rocks over long time scales, for example, by increasing the acidity of water in the soil, increasing the substrate surface area, and affecting the hydrologic cycle. Increased weathering rates affect the geologic carbon cycle by lowering CO2 concentrations in the atmosphere. Furthermore, it has been proposed that the onset of photosynthesis aided in the construction of continents by causing chemical disequilibrium in saltwater.

These are only a few of the many ways that life changes the environment, which changes the abiotic circumstances in which life thrives. As a result, we deal with interactions between the atmosphere and the biosphere, as well as the geosphere and the biosphere. These interactions occur on time ranges ranging from seconds (e.g. leaf temperature) to the planet's history (e.g. formation of continents). These interactions, depending on how powerful they are and how important they are, should be significant in understanding the current state of Earth, life, and its historical co-evolution.

However, it is unclear how we would quantify the relative influence of biotic processes on the environment in general. In this study, I look at biotic activities in terms of their involvement in causing thermodynamic disequilibrium, which should provide us with a quantitative and fundamental foundation for assessing the value of life on the planet.

Thermodynamics of widespread life within the Earth system:

We may now ask more fundamental questions about the nature of these interactions and why they are likely to develop within the complex Earth system now that the concept of atmosphere–biosphere–geosphere interactions are generally well understood. Why does life alter the environment in such a way? Is it merely a historical coincidence that biotic effects occur, or do they act in a certain direction? How can we reconcile specific biotic influences with potentially basic trends that characterize how the entire Earth system functions and evolves over time?

Thermodynamics is a fundamental physics theory that allows us to answer these concerns. The first and second laws are fundamental to thermodynamics. While the first rule of thermodynamics specifies the amount of work that may be derived from temperature gradients under the constraint of energy conservation, the second law informs us about the irreversibility of processes and so gives us an "arrow of time." The most common applications of thermodynamics are in engineering, such as the Carnot cycle of heat engines and freezers. 

Thermodynamics has also been used to study physical processes in the Earth system, such as atmospheric motion generation and dissipation, hurricane intensity, hydrological processes at the land surface, the atmospheric branch of the hydrologic cycle, ocean dynamics, and, of course, geochemical transformations. These processes function in steady states where they optimize their dissipative activity, or, roughly equivalently, maximize power generation or entropy production (the suggested Maximum Entropy Production (MEP) principle).

Thermodynamics must also apply to living creatures, as Boltzmann and Schroedinger pointed out. Life fuels its metabolism and maintains its structure by eating low entropy "food" and rejecting high entropy "waste" products and heat. Living organisms, like any other dissipative activity, keep their state away from thermodynamic equilibrium by exporting entropy to the environment on a net basis. Because of the similarity of living organisms and purely physical dissipative processes, Lovelock and Margulis coined the term "superorganism" to describe Earth. The same thermodynamic maximizing concepts are used to characterize the structure of the steady-state that describes the sum of all living creatures in an ecosystem on a small scale or in the biosphere on a large scale.

The ability to merge these elements into a single huge image of the entire world has been mostly lacking. Thermodynamics is an obvious choice for a language to depict such a picture since its formulations are so generic that we may use the same word to describe any Earth system operations. We can better comprehend the interactions between Earth system processes and life when we do so, and link them to the degree to which the system is kept out of thermodynamic equilibrium. Applying thermodynamic organizational concepts to these interactions, such as maximum power or MEP, may help us better understand how the entire Earth system acts in a steady-state, as well as how regulatory mechanisms and feedbacks work.

Developing a theory of life within the hierarchical Earth system:

Here, Axel Kleidon develop a theory of the entire Earth system based on non-equilibrium thermodynamics to link life and the thermodynamic condition of planet Earth. From radiative exchange to motion to geochemical cycle, this theory presents a hierarchical view of Earth system processes in which activities generate free energy, dissipate it, but most significantly, transfer power from one process to another higher up in the hierarchy. The first and second laws of thermodynamics establish the criteria for operating these power transfer processes, as well as the maximum rates of power creation and transmission and how these processes interact. The maximum power principle (or, more closely related, MEP) states that there should be characteristic maximum transfer rates, which define upper constraints on how much power can be exchanged across devices.

Radiative fluxes at the Earth–space interface cause radiative heating and cooling to differ spatially and temporally. The heat engine that causes motion inside the atmosphere, as shown by the engine symbol in the illustration, is fueled by the temperature differences that result. The flow's kinetic energy lifts moist air, cools it, and brings it to saturation, condensation, and precipitation, removing water from the atmosphere. As demonstrated by the "belt" around the engine symbol in the illustration, the atmospheric heat engine powers the atmospheric dehumidifier in this way. This dehumidifier serves as yet another engine in the global water cycle. The hydrologic cycle sends water to land at a higher height than sea level, allowing continental runoff to propel dissolved ions and sediments to the seafloor. The geochemical cycling of rock-based elements is the result of this "transporter" of continental material interacting with the inner processes of the global rock cycle.

Because dissipative processes would inevitably tend to slow down the engines and result in inefficiencies, the emergent dynamics of this hierarchy, and specifically the consequent extent of chemical disequilibrium, is largely influenced by how much power is exchanged among each of the processes. Abiotic processes can only drive and maintain states of chemical disequilibrium to a limited amount due to inherent inefficiencies in each of the transfer mechanisms. Photosynthetic life, on the other hand, is able to directly tap into the power inherent in the flux of solar radiation, bypassing the numerous inefficiencies found in abiotic power transfer mechanisms, and hence is able to drive and maintain significant chemical disequilibrium states. As a result, life is crucial in driving and maintaining planetary instability.

We should be able to quantify the extent to which life contributes to disequilibrium using thermodynamics. To do so, we must first comprehend both the power transfer and the power that drives the main hierarchy of Earth system processes that is connected with the geochemical cycle. The power associated with biotic activity must then be estimated and compared to the power involved in abiotic geochemical processes. The thermodynamic character of interactions among processes and related maximum power states will thus play a vital role in the functioning of the entire Earth system, resulting in a holistic, thermodynamic description of life within the Earth system.