Can the Gaia Hypothesis Be Tested in the Lab?

During the 1970s, inventor/environmentalist James Lovelock and evolutionary biologist Lynn Margulis proposed the Gaia Hypothesis. This theory posits that Earth is a single, self-regulating system where the atmosphere, hydrosphere, all life, and their inorganic surroundings work together to maintain the conditions for life on the planet. This theory was largely inspired by Lovelock’s work with NASA during the 1960s, where the skilled inventor designed instruments for modeling the climate of Mars and other planets in the Solar System.

According to this theory, planets like Earth would slowly grow warmer and their oceans more acidic without a biosphere that regulates temperature and ensures climate stability. While the theory was readily accepted among environmentalists and climatologists, many in the scientific community have remained skeptical since it was proposed. Until now, it has been impossible to test this theory because it involves forces that work on a planetary scale. But in a recent paper, a team of Spanish scientists proposed an experimental system incorporating synthetic biology that could test the theory on a small scale.

The team included researchers from the Catalan Institution for Research and Advanced Studies (ICREA), the Universitat Pompeu Fabra’s Complex Systems Lab (UPE-CSL), the European Molecular Biology Laboratory (EMBL), and the Santa Fe Institute (SFI). Their paper, “A Synthetic Microbial Daisyworld: Planetary Regulation in the Test Tube,” recently appeared in the Journal of the Royal Society Interface. As they describe, their proposed test consists of two engineered micro-organisms in a self-contained system to see if they can achieve a stable equilibrium.

An image of Earth taken by the Galileo spacecraft in 1990. Credit: NASA/JPL

In response to challenges, Lovelock and British marine and atmospheric scientist Andrew Watson (a postgrad student of Lovelock’s) created a computer model named Daisyworld in 1983. The model consisted of an imaginary planet orbiting a star whose radiant energy slowly increases or decreases (aka. stellar flux). In the first (biological) case, the planet has a simple biosphere consisting of two species of daisies with different colors (black and white) that cause them to absorb different amounts of solar radiation.

The black or white daises increase based on how much solar energy the planet receives, and changes in their relative populations stabilize the planet’s climate over time despite fluctuations in energy from the star. In the second (non-biological) case, the planet’s temperature is directly related to the amount of energy it receives from the star. Previously, no means existed to test this model since it was planetary in scale. This proposed test was inspired by recent research in fermentation, which typically requires finely tuned external controls to ensure stable, regulated conditions.

In this experimental setup, one strain senses if the environment is becoming too acidic and counteracts it, while the other strain senses if the environment is becoming too basic and acts to increase acidity. Ricard Solé, an ICREA research professor, head of the Complex Systems Lab, and an external professor at the SFI, was a co-author of the paper. As he explained in a recent SFI news release:

“There’s been recent work in trying to see if you can engineer microorganisms for fermentation so that they can self-regulate. That was the key inspiration. Because these strains act on the environment, and the environment affects them, this creates a closed causal loop. The idea is to show that under very broad conditions, they will stabilize to a constant pH level, as predicted by the original theory.”

Artist’s impression of an Earth-like exoplanet orbiting Gliese 667 C, part of a triple star system. Credit: ESO

Solé and several of his students developed the experiment during a visit to SFI. It has the potential to answer long-standing questions regarding planet-wide regulatory systems. In short, it offers the first possible means for testing the Gaia Hypothesis and demonstrating the vital role life plays in regulating biospheres and maintaining habitable conditions. In addition to Earth’s climate, this research could have significant implications for measuring habitability and climate stability on other planets, particularly exoplanets.

Further Reading: Santa Fe Institute, Journal of the Royal Society