Thermodynamics and life Past, Present and Future of the use of energy by living beings

Resumen

Life emerged on Earth more than 3.5 Gyr ago and it has been using energy ever since. The purpose of this thesis is to study several aspects of the relationship between energy and life. First, I start with the analysis of the nitrogen requirements of life in the Early Earth, and conclude that life was not able to produce enough biological nitrogen by itself, meaning that other sources of energy were required by the time. In the course of evolution, life developed the ability to use the solar energy that reached the surface of our planet, and its use modified not only the evolution of the living beings but also the evolution of the atmosphere. The changes in the atmosphere were followed by changes in the maximum efficiency in the energy obtainable from solar radiation. On a different aspect, it is believed that Mars was inside the so-called habitable zone once, where liquid water exists and the conditions are suitable for life, but now the environment is dry and harsh. Despite the fact that we have not found life so far in the planet, a biosphere might be living beneath the regolith and chemolithotrophic organisms could be using chemical energy to survive in the current martian environment. I analyse the energetic features of the present day near-surface martian atmosphere using the state-of-the-art knowledge of the thermodynamic variables nowadays, provided by rovers and satellites. As many of those spacecrafts are powered with solar energy, the knowledge of the maximum obtainable work of solar cells in the environment of Mars is extremely important for the future of exploration and colonization of the planet. I provide clues on the maximum efficiency of solar radiation in the planet under different conditions.