Gaia Hypothesis

The Gaia hypothesis holds that the earth itself is a living organism. Associated most closely with the work of atmospheric chemist James Lovelock and microbiologist Lynn Margulis, the Gaia hypothesis is interpreted by some as a metaphor for how we should think about the earth and by others as a literally true description of the earth.

The Gaia hypothesis can be best understood in contrast to the alternative, which views the earth's biological and abiotic processes as independent of one another. From that perspective, the planet's geophysical processes, from plate tectonics and climate to atmospheric and oceanographic conditions, simply provide the physical context in which life evolves and exists. In contrast, the Gaia hypothesis emphasizes the effects that biological processes have in creating and maintaining geophysical conditions.

In one version, often referred to as the weak Gaia hypothesis, the hypothesis suggests only that living organisms alter the abiotic conditions in which they live in ways that result in a more hospitable environment. A more radical version, often called the strong Gaia hypothesis, postulates the earth as a living superorganism, which, by design or conscious intent, maintains the balance of abiotic conditions necessary to support its own life.

Lovelock's initial hypothesis was stimulated in the 1960s by his study of the striking contrast between the atmospheres of Venus, Mars, and Earth. The atmospheres of both Venus and Mars are in equilibrium that is chemically inert, consisting of more than 95% CO2. In contrast, Earth's atmosphere is also in equilibrium but is composed of a gaseous mixture (77% nitrogen, 21% oxygen) that should be chemically reactive and unstable. Lovelock sought a hypothesis to explain this anomaly and was struck by the parallel with biological homeostasis. In simple terms, the atmospheric equilibrium was maintained through a complex and dynamic interrelationship between the biotic and abiotic processes on earth.

Biological homeostasis is the property of living systems to maintain the internal equilibrium necessary for life. For example, the human body must maintain such features as temperature, salinity, nutrients, blood pressure, wastes, water, and oxygen within certain levels in order to remain alive. Biological systems maintain homeostasis through a variety of processes, including respiration, metabolism, sweating, shivering, excretion, and food ingestion. A series of physical, chemical, and biological processes work together in a complex system of feedback loops to produce and maintain the conditions necessary for life. Some might even say that this very interaction of physical and chemical processes of working together to maintain equilibrium is life itself.

Lovelock's initial hypothesis was that the earth is itself a living system. The earth can be understood as existing in a state of homeostasis in which physical, chemical, and biological processes work together to maintain a systemic equilibrium necessary for life. Photosynthesis is a paradigmatic example of such interaction. Life (in this case plants) creates, through a physical (solar energy) and chemical (water and carbon dioxide) process, the conditions (oxygen and carbohydrates) by which life can be maintained. Lovelock named this self-regulating living system after the Greek earth goddess Gaia.

The Gaia hypothesis was immediately challenged by a wide range of critics. The fact that it had been adopted by a diverse collection of New Age religions, mystics, and many environmentalists only added to its scientific disparagement. Scientific critics tended to focus on the stronger versions of the hypothesis in which purposive, intentional, and teleological categories were attributed to the Earth. Scientific criticisms especially rejected the teleological aspects of the hypothesis and denied that it was testable.

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