Earth is the only known inhabited planet, and the geological record demonstrates that life and Earth have co-evolved for billions of years in a closely linked system. Life is sustained by energy and material exchanges among Earth’s interior, Earth’s surface, and the Sun. In turn, life has changed the surface chemistry of Earth. These changes have propagated into Earth's interior through subduction. Through time, the mantle, lithosphere, hydrosphere, atmosphere, and biosphere have slowly evolved, with intervals of rapid change due to historical events (e.g. impacts, evolution of land plants, etc.). Both incremental evolution and historical events are reflected in the co-evolution of Earth and life. This evolution is reflected in biogeochemical cycles that extend from the mantle to the top of the atmosphere, with ecosystems evolving in response to perturbations and inducing planetary-scale changes in Earth’s surface processes.
The field of Geobiology focuses on understanding these changes using diverse fields of study. Geobiologists can study modern life through ecology, organismal processes, genetics, and biogeochemistry. They can study the history of these interactions through geological studies, paleontology, geochemical approaches, and modeling. They can study these processes on other planets by applying what we understand of interactions on Earth to our observations from missions and telescopes. The key aspect that makes a study part of Geobiology is that it provides insights into how life and Earth (or other planets or moons) interact through time.
Sometimes it helps to look at a simplified system to understand a more complex one. The rest of this chapter introduces a very simple biosphere on a very simple world: daisies on a planet that receives energy from a star. We ignore all the biological aspects of daisies except their preferred temperature for sprouting and growth. It is still an interesting planet!
Thumbnail: An artist's impression of ice age Earth at glacial maximum. CC-BY-SA 3.0 Unported; Ittiz via wikipedia).
- 1.1: Daisyworld
- Daisyworld illustrates the importance of interactions between life and Earth.