What Are the Necessary Conditions for Origin of Life and Subsequent Planetary Life-support Systems?

In this chapter, some questions regarding the origin of life and the coevolution of the biosphere and geosphere are discussed. According to the Gaia theory, the environment is influenced by and for the benefit of the biosphere, but whether this occurs on all timescales is uncertain. Feedback from the biota to the geosphere is particularly strong for the composition of the atmosphere.

Coevolution of the geosphere and biosphere may be investigated using a simple Earth system model. The scenario of an Archaean hothouse with a thermophilic early biosphere is presented. The life span of a photosynthesis-based biosphere is limited by the atmospheric content of carbon dioxide. The simplest living being is a prokaryotic cell organism. The interactions between biosphere and geosphere are realized via the cycling of elements such as carbon, phosphorus, nitrogen, and sulfur, where the carbon cycle is the most important. To evaluate the present Earth system, which is in a state of optimum self-regulation, an extended model is used that includes three different types of biosphere: prokaryotes, eukaryotes, and complex life, where prokaryotes are always the base for higher types of biosphere.