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 first part of this chapter introduces a very simple biosphere on a very simple world: Daisyworld (Watson and Lovelock, 1983). Black and white daisies on a planet receive energy from a star and influence the planet's temperature. We ignore all the biological aspects of daisies except their preferred temperature for sprouting and growth, plus their need for somewhere to grow. Even though Daisyworld represents a very simple ecosystem, it is still an interesting planet!
The second part of this chapter discusses some of the interactions among organisms that create complexity in ecosystems. In all cases, these interactions occur in the context of our planet and the resources it provides. While reading about interactions types, think about the interactions among the daisies in Daisyworld. How many different types of interactions are there? Can they be classified into the interaction types described in the second part of the chapter? If this was a real ecosystem, what other organisms would be needed to allow the daisies to grow? How would any of these needs affect the simple Daisyworld model?
Thumbnail: An artist's impression of ice age Earth at glacial maximum. CC-BY-SA 3.0 Unported; Ittiz via wikipedia).
Watson, Andrew J. & James E. Lovelock (1983) Biological homeostasis of the global environment: the parable of Daisyworld, Tellus B: Chemical and Physical Meteorology, 35:4, 284-289, DOI: 10.3402/tellusb.v35i4.14616)