The "Goldilocks" planet
There are an array of factors necessary for life to exist and getting each of them "just right" is pivotal. For life to exist at all, a planet must be just far away from a star to ensure that water is liquid to support carbon-based organisms (like us!). If a planet meets these conditions, it's said to be in the Habitable Zone. Earth has hit the nail on the head, being 93,000,000 miles from the sun. But this has only set the stage for life. How can we account for the relative stability of Earth's ecology?
There are several sustained ecological phenomenons that cannot be explained by Earth's ideal position from the sun. For example, oxygen is the second most reactive element and should not be stable with methane present. How then have atmospheric concentrations of gases remained constant? How have the oceans kept salinity around 3.4% despite salts being constantly introduced by rivers? How has Earth maintained regular fluctuations in temperature despite an increase in the energy output from the sun (regardless of the acceleration recently observed)?
Enter the gaia hypothesis...
After working with NASA in search of life on Mars in the 1960s, James Lovelock coined what was originally called the Earth Feedback Hypothesis. It was later named Gaia after the Greek goddess of the Earth. Essentially, Gaia Hypothesis posits that organic and inorganic components of the earth evolved together as a single, self regulating organism. Together, interacting ecosystems compose a single huge ecosystem at the Earth's surface. This interaction, connecting all organic and inorganic components of the Earth, is essential in maintaining Earth's ability to sustain life. Noted microbiologist Dr. Lynn Margulis has been an important collaborator in the hypothesis.
How the earth regulates itself
Examining the same three phenomenon of ocean salinity, atmospheric concentration and temperature regulation reveals the feedback mechanisms behind Gaia theory.
- Oxygen: When photosynthetic organisms evolved, oxygen was introduced to the atmosphere. Since its aggregation, it has remained stable at 21% for a long period of time. If the concentration raised even to 25%, biomass would be significantly more combustible. Thus it is suggested that photosynthetic organisms work systematically to keep oxygen levels conducive for metabolism but low enough preventing of rampant wildfires.
- Ocean salinity: In order for metabolic processes to occur, ocean salinity cannot rise about 5%. Despite rivers carrying dissolved salt from rocks into the ocean, the salinity has remained constant around 3.4% for a very long time. Evidence now supports that salt it removed and recycled through cracks in the ocean floor. Here we see geology working with salinity to maintain life.
- Atmospheric temperature: The energy the sun emits has increased from 25% to 30% since life began on Earth, but temperature has remained within the habitable zone (including significant highs and lows). Clouds are instrumental in the maintenance of climactic temperature. Interestingly, cloud formation over the ocean has been shown to be a specific function of algae emitting a sulfur molecule that becomes the condensation nuclei for raindrops, revealing a biotic motivation for this occurrence.
Gaia's place as an explanatory model
When the Gaia Hypothesis was introduced by Lovelock, several scientists resisted it as a credible explanatory model. However, following several supportive scientific experiments revealing the predictive power of the hypothesis, it is now considered a theory and has gained significant merit. For example, Lovelock's "Daisyworld" experiment revealed how different varieties of daisies will selectively grow to keep their environment sustainable for life.
The main message of Gaia Theory is that there is an inherent property of interaction among all organisms, creating a surface that cooperates as one physiological system in certain ways. It was eloquently summarized in Margulis' most recent book The Symbiotic Planet as "symbiosis seen from space".
Gaia Theory has infinite application potential, emphasizing the interconnectedness of all components of Earth. It has become important in the prediction and study of climate change, for example. Regarding Earth as an entirely interconnected and symbiotic system underscores the true beauty of life and the need to support health, happiness and harmony amongst all aspects of life. This perspective brings us to see our actions as permeating and holding the potential for both positive and negative ripple effects.