10 Compelling Pieces of Evidence that Support the Gaia Hypothesis

There’s little doubt that life itself is a driving force in evolution, but does that mean that organisms co-evolve as the Gaia hypothesis suggests?

The Gaia hypothesis suggests that all life on Earth forms part of a co-evolving entity that’s akin to a single living organism. Since the development of the hypothesis by chemist James Lovelock and microbiologist Lunn Margulis in the 1970s, it has been subject to no small amount of criticism. In more recent years, however, acceptance of the hypothesis is growing, particularly in light of mankind’s increasing influence on the environment. Some scientists even now consider it to be a theory rather than a hypothesis, even if it is one with a lot of holes in it. Nonetheless, there’s little doubt that there’s at least some truth in it, as the following evidence illustrates:

#1. Atmospheric Oxygen

Billions of years ago, Earth’s atmosphere consisted mostly of nitrogen and carbon dioxide, created by volcanic activity and impact events. There was no free oxygen, making the planet uninhabitable to most life that exists today. However, photosynthesising cyanobacteria first appeared around 3.5 billion years ago, producing oxygen as a by-product. Initially, the oxygen was absorbed by the atmosphere to form deposits of rust on the sea floor. Around 2.3 billion years ago, however, cyanobacteria became so prolific that it created more oxygen than the atmosphere could absorb, thus forming the breathable air that life relies on today.

#2. Ocean Salinity

Salt levels in the Earth’s oceans have been fairly consistent for an extremely long time, hovering around the 3.4% mark. Most ocean-dwelling life cannot tolerate salinity levels much higher than this, hence the reason why the Dead Sea is, well, dead. Although the scientific community is still not sure exactly what causes ocean salinity levels to remain stable, an increasingly popular theory suggests that it may be thanks, at least partially, to biological processes. The theory suggests that bacterial colonies create ocean salinity-regulating salt flats by fixing ions and heavy metals as part of their life processes.

#3. Global Warming

When life first appeared on Earth, the energy output from the Sun was as much as a third lower than it is today, which suggests that the planet should have been too cold to support the development of complex life. However, biological influences on global warming have existed since the very beginning thanks to the production of powerful greenhouse gasses like methane and carbon dioxide. In fact, throughout most of the planet’s history, Earth has been significantly warmer than it is now. Without naturally occurring greenhouse gasses, such as those produced by either tectonic activity or life itself, Earth’s current average surface temperature would be -18°C.

#4. Daisyworld and Albedo

Greenhouse gasses are not the only thing that keep Earth’s temperatures in check. The Daisyworld simulations, created in support of the Gaia hypothesis, suggests how the colour of living organisms can also influence temperatures. The simulations examine how organisms, namely plants in this case, change the albedo (reflectivity) of the planet. For example, darker organisms would absorb more light, thus helping to heat the surface, whereas lighter colours reflect light and heat, keeping the surface cooler. Ultimately, the Daisyworld model suggests that healthy competition between organisms helps to keep the climate in check.

#5. Human Impact

For many years, the Gaia hypothesis was considered by many among the scientific community as a pseudoscience beloved of New Age hippies. However, there is now rapidly increasing evidence that manmade factors are influencing the environment to such an extent that it’s throwing the Earth’s biosphere out of kilter and effectively overpowering ‘Gaia’. Current extinction rates are between 1,000 and 10,000 times higher than the natural background rate, and atmospheric CO2 levels have increased by almost 50% since the beginning of the Industrial Revolution. Even if nature and Mother Earth are one, it seems humankind alone is stronger.

#6. Viruses and Evolution

Biologists are still not unanimously agreed as to whether viruses are a form of life or not. They possess genes and themselves evolve by natural selection. At the same time, however, they cannot function without a host cell, thus having no ability to metabolise on their own. We tend to think of viruses as a bad thing, but that’s not the whole story. In fact, they are one of the driving forces in evolution due to their ability to transfer genetic information between different species and increase genetic diversity. As such, viruses played a particularly important role in early ecosystems when all life was microbial – without viruses, complex life could never have evolved.

#7. Symbiotic Organisms

While the strong Gaia hypothesis, as portrayed in the James Cameron film Avatar, belongs to the world of pseudoscience, symbiosis is still an extremely important part of nature. Some species have evolved to become reliant on others to the extent they cannot survive independently. These symbiotic arrangements may be mutually beneficial, parasitic or beneficial for one organism but irrelevant to the other (commensal). For example, most vascular plants have symbiotic relationships with fungi. At the same time, animals cannot survive without the crucial role that certain microorganisms have in everything from digestion to immune systems.

#8. Sulphur Production

In 2012, a team of geologists at the University of Maryland found that the essential role of sulphur in Earth’s ecosystems could either prove or disprove the validity of the Gaia hypothesis. Sulphur is one of the many elements that are critical to life, albeit in relatively small amounts. Building upon research from the 70s, it looks at how marine microbes metabolise dimethylsulfoniopropionate (DMSP), a radioactive isotope of sulphur, into dimethylsulphide, thus transporting it into the atmosphere. This biologically formed sulphur cycle plays a crucial role in regulating the climate to the extent that it may even influence the planet’s radiation balance.

#9. Biodiversity

Evidence is all around us that biodiversity itself plays one of the most important roles of all in keeping the Earth’s ecosystems working. After all, it sometimes only takes one extinction to bring about countless more. For example, without pollinators like bees and butterflies, most flowering plants would be unable to reproduce. Forming the basis of modern ecosystems, a world without bees would be a world without almost any of the crops we rely on today or the plants that countless other species rely on. Biodiversity would collapse, taking millions of years to recover, and our breathable atmosphere could also transform with further catastrophic consequences.

#10. Earth from Space

The Gaia hypothesis quickly became popular following mankind’s first explorations of space which, of course, allowed us to view the world in a way we had never done before. From this extraterrestrial viewpoint, it is easier to imagine the Earth functioning as a single organism, characterised by its life-giving hues of blue and green. Earth as seen from space perfectly exemplifies the role of biological chemistry in our living world. You can see that life is abundant in almost every region of the globe, and that’s partly because of life’s regulatory role in everything from the amount of salt in the sea to the percentage of oxygen in our atmosphere.

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While the Gaia hypothesis might be controversial, it does illustrate the obligation mankind has to protect its environment and give nature space to breathe. Do you think of the Earth as a single living superorganism composed of elements working in healthy competition together? Or, perhaps, is life inherently suicidal, as the opposing Media hypothesis suggests? Let me know your thoughts in the comments below!

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