Chapter 4

Planetary systems that harbor life: Early Earth as an example

Synopsis

Among the millions of events occurring at the origin of the Universe and the emergence of our solar system,  one of them is particularly important to us, humans: the formation of Earth and the unique characteristics of this planet that supported the origin and evolution of a wide diversity of life forms. In this chapter, we elaborate on the formation of Earth and the prebiotic, early Earth environment. We discuss different ideas regarding  the availability and chemistry of organic and inorganic molecules that might have been instrumental in setting the stage for the emergence of life. The chapter follows with a discussion on certain peculiarities of the early Earth's environment and the plausible scenarios that might have provided the necessary sources of raw materials and energy, the synthesis of molecules essential to form the first living cells, and enzyme-free routes for the synthesis of monomers and polymers of the important biomolecules of life, such as nucleic acids and proteins. Assuming the formation and viable propagation of these molecules, the transition from chemistry to biology toward the formation of the protocells is also discussed in detail. Finally, we delve on how our current understanding of prebiotic chemistry and the origin of life on Earth can help us in the exploration of biosignatures and life beyond Earth.