It has been almost a century since the inquiry into life's origin has been reinvigorated following several decades of quiescence influenced by Louis Pasteur's elegant experimental demonstration that microbes were not spontaneously generated in flasks of nutrient broth appropriately aerated to prevent the entry of airborne particles. It has been a century in which biochemistry and biophysics have completely altered our core understanding of the living world and consequently opened up a series of powerful experimental, theoretical, and computational approaches. In this new light, two of us independently thinking of first life were some fifteen years ago introduced by colleagues at the Santa Fe Institute who had detected some common points of interest in what we were investigating, one from the top down and the other from the bottom up – from the phenomenology of the living world with an emphasis on biochemistry and biophysics and from the underlying physics and chemistry and statistical theory that impose a necessary order.

A common theme was that life on Earth was not the outcome of an isolated event as suggested by the Chance and Necessity school but a planetary property that appeared early in the history of the planet and spread in a spontaneous way. What we designate life or proto-life has existed over most of the lifetime of planet Earth. The universality of the phenomenon and the massive flux of matter and energy due to the huge interaction of organisms and their products with the rest of planetary matter led us to return to the perceptive book Geochemistry by Kalervo Rankama and Th. G. Sahama [664], a work highly praised to one of us by the polymath G. Evelyn Hutchinson, dean of American ecologists. The two Finnish geochemists, acting as geological generalists, divided the planet into four geospheres: the lithosphere, the hydrosphere, the atmosphere, and the biosphere. The term “biosphere” had been introduced in 1875 by Eduard Suess and used in its modern sense some years later by the perceptive geochemist Vladimir Vernadsky.

What we wish to understand from a scientific point of view is how the newly formed planet, condensing approximately 4.6 billion years ago, was transformed over time into the present verdant world, home to millions of species and the abode of Homo sapiens, a taxon including individuals like ourselves, who are somehow impelled to ask the foundational questions that this work tries to answer.