Field of Science


"Surface conditions on Earth, have been for most of geological time regulated by life…[]…This new link between Geology and Biology originated in the Gaia hypothesis''
NASA geologist Paul Lowman (2002)

The concept of a living planet is a rare but intriguing vision of pop-art and science-fiction. In the Italian movie "Planet on the Prowl" (1966) the gravitational pull of a planet is causing havoc on earth. A team is send into space to destroy the planet, but here they discover that the celestial body is a living (!) cybernetic organism (however artificial in origin) that will not simply surrender without fight. A very similar plot was already used by director Antonio Margheriti in "Battle of the Worlds" (1961), where the mainframe of an alien spaceship is mimicking a planet.
A classic approach to a planet as life form is found in comics in the shape of the evil characters of Ego the living planet ("Thor" Sept. 1966) and Mogo the living planet ("Green Lantern" May 1985). Both planets are self-concious and selfish entities that feed on other worlds.

In 1965 the independent scientist James Lovelock, inspired by research on the possible habitability  of planet Mars, proposed in a Nature-article to see the various spheres of earth (lithosphere, hydrosphere, biosphere and atmosphere) as an interconnected and self-regulating system. He followed the suggestions by novelist William Golding and called this idea the Gaia-hypothesis, after the ancient mythological titan Gaia - personification of earth (this unintentionally, but supposed religious connection caused most concern in the scientific community). However the general notion that the Gaia-hypothesis states that "earth as a living planet" or a "life form" in the sense of entity or even individual is incorrect.

Fig.1. "SimEarth" is a simulator for life-supporting planets, 1990-1992 by Maxis.

Lovelock argued that both biotic and abiotic processes limit the possible amplitude of changes in the salinity of the oceans, the surface temperature of earth and the atmospheric chemistry - therefore forcing earth into a life-supporting disequilibrium between two stable extremes like the frozen wasteland of Mars or a hellish world as Venus.

In 1971 microbiologist Lynn Margulis (1938-2011) joined Lovelock (here an interview with both scientists in 2011), emphasizing the significance of microbial life and activity for the Gaia-theory and arguing how natural selection, acting on single individuals, could account for the development of (apparently) stable systems. Egoistic organism do not manipulate deliberately the system so it can support them; however if an organisms harms his environment (and the life-supporting properties) it will be naturally selected and be removed from the system. Environments are also not static systems that will not react to biotic changes, but can oscillate around "set points" without loosing their life-supporting properties.

"Some 30 million types of extant organisms have descended with modification from common ancestors; that is, all have evolved. All of them-ultimately bacteria or products of symbioses of bacteria - produce reactive gases to and remove them from the atmosphere, the soil, and the fresh and saline waters. All directly or indirectly interact with each other and with the chemical constituents of their environment, including organic compounds, metal ions, salts, gases, and water. Taken together, the flora, fauna, and the microbiota (microbial biomass), confined to the lower troposphere and the upper lithosphere, is called the biota. The metabolism, growth, and multiple interactions of the biota modulate the temperature, acidity-alkalinity, and, with respect to chemically reactive gases, atmospheric composition at the Earth's surface."

Margulis also emphasized the link between geology and biology - for example:
Plate tectonics is like life (as we at the moment know) a unique feature of the planet Earth. Apart of the size, density and petrological composition, plate tectonics seems to depend from the existence of liquid water on a planet. Without an atmosphere, earth would be to cold to maintain water in liquid form; however the chemistry of the atmosphere is influenced both by the lithosphere (by volcanic eruptions) and controlled by the carbon-circle of the biosphere. Finally plate tectonics modified (and modifies) the surface of earth and the environments, forcing life forms to adapt and evolve - probably even with no plate tectonics life would be still possible on earth, but it surely would be much more monotonous.
So every subsystem is connected to the others and influence them, being at the same moment influenced by all other subsystems.

Today´s legacy of Lovelock and Margulis is the consideration to see geology as part of the Earth System Sciences and appropriately to understand the Earth as a system.


MARGULIS, L. (2004): Gaia by Any Other Name. In (ed.) Schneider S.H. "Scientists Debate Gaia - The Next Century": 7 - 12

1 comment:

  1. The most recent employment of the Gaia concept for entertainment was in the movie Avatar, albeit on a foreign planet. There have actually been symposia held on Gaia.


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