Over 50 years ago, scientist James Lovelock hit upon the idea that Earth is a complex, self-regulating organism. At the suggestion of a friend, novelist William Golding, he called his idea the Gaia hypothesis, after the Greek goddess who symbolizes Earth.
Simply put, the Gaia hypothesis says that Earth is a living system and uses similar mechanisms that living creatures use to stay alive, by constantly regulating temperature, chemical and physical inputs and outputs and adaptation through evolution.
Lovelock, who turned 101 in 2021, came up with his idea in the 1960s, when NASA asked him to see if his inventions in chemical analysis could detect life on other planets by looking at their atmospheres.
Venus, our nearest neighbor at 25 million miles closer to the Sun than Earth, is literally a hot mess, with steady surface temperatures of nearly 900 degrees Fahrenheit and an atmosphere of mostly carbon dioxide laced with bits of sulfur droplets — not hospitable for life forms we know.
Mars, 100 million miles further from the Sun than Earth, is a bit less hostile to life, with days of searing heat and nights of deep cold. It also has an atmosphere overwhelmingly made up of carbon dioxide, with just tiny traces of oxygen.
Lovelock’s insight came when he realized that the bigger question was not, "Is there life on those other planets?" but rather, "Why is there life here on Earth?"
Like Venus and Mars, Earth has strong volcanos that, over time, have spewed out huge amounts of carbon dioxide. These volcanos should have created a hothouse or a desert on Earth. But something has kept carbon dioxide levels in a sweet spot: just four hundredths of a percent of the Earth’s atmosphere, enough to keep it warm, but not too warm, for life, while the oxygen needed for animals is in great abundance — and that something is life itself.
About a billion years after Earth was formed, photosynthesis evolved. Photosynthesis is how plants, algae and other organisms convert sunlight into chemical energy and break down CO2 into its elements, carbon and oxygen. Over millions of years, plants and algae sequestered in their cells all that carbon from volcanos, and when buried in the ground or under the sea, some of it eventually became coal and oil.
Four times in Earth’s geologic history, giant eruptions of volcanoes belched out so much CO2 they set off mass extinctions. A separate mass extinction was linked to an asteroid strike that likely shut down a lot of Earth’s photosynthesis and allowed CO2 levels to rise.
After each of these cataclysmic events, Earth had to start sequestering carbon again, as life evolved to adapt to new conditions. So, when we drill and dig up fossil fuels today, we are upsetting a balance the Earth works hard to keep. But if we keep those fossil fuels in the ground, we help support the living planet.
Many scientists have helped advance the Gaia hypothesis — now known as Gaia theory — over time. One of the most public voices is Stephan Harding, a former student of James Lovelock. Harding is now a deep ecology research fellow at Schumacher College in England.
In sum, he says, every living plant and animal on Earth interacts with nonliving rocks, atmosphere and water to make the planet an independent, living organism.
"It's the ability of the whole, of all four of them working together — life, atmosphere, rocks and water — working together to keep the surface conditions on the planet suitable or within the limits that life can tolerate. "
“The scientific idea is that when they start interacting with each other, these four components, something extraordinary emerges out of those interactions which you couldn't have known in advance. It's called an emergent property,” Harding explains. "It's the ability of the whole, of all four of them working together — life, atmosphere, rocks and water — working together to keep the surface conditions on the planet suitable or within the limits that life can tolerate. Life has a very important role here. Life is intimately involved in regulating the temperature, the acidity of the planet, the distribution of key elements. And so, the idea suggests that the Earth is one great living organism. “
And as thinking about Gaia has evolved, more credence has been given to the notion that not just biologically active beings, but also the so-called inanimate things like rocks and water, can support life. Observations reveal countless examples of the ways in which life, in its many forms, regulate the planet.
"So just think of that: Living beings are actually helping to cool the surface of the planet. I mean, that’s amazing .”
“Basically, we now know that many kinds of organisms, including marine algae and forests, like rain forests,…emit chemicals that seed clouds,” Harding says. “And those clouds are dense and white and they cool the Earth. And this is happening over the rain forests and over parts of the ocean. So just think of that: Living beings are actually helping to cool the surface of the planet. I mean, that’s amazing .”
Harding says scientists are pretty sure they understand how Gaia has regulated temperature over geological time. Volcanoes continually emit carbon dioxide into the atmosphere while, simultaneously, the sun grew brighter — about 30% brighter now than it was when life began on Earth about 4 billion years ago.
These two conditions — increasing CO2 in the atmosphere and the increasing brightness of the sun — are “a recipe for an absolute disaster for life,” Harding says. “Eventually the planet will get so hot…all the water would evaporate — boil off, like in a kettle. It's called a runaway greenhouse. That's what happened on Venus. But it didn't happen on Earth because of life — because of life interacting, holding the water down, capturing the hydrogen as it was trying to flee.”
Today, some people dismiss the Gaia hypothesis and the role of rocks and water in life as a pseudo-intellectual exercise that seeks to put a more acceptable face on animistic beliefs of aboriginal societies. But Stephan Harding believes we are all born with an intrinsic understanding of Gaia.
“It's just our natural humanity to feel the Earth as alive and as a mother. It’s built into us,” he says.
Yet modernity, he says, is headed for extinction because of the way we currently relate to Gaia.
“We don't relate to Gaia with our aboriginality; we relate to her through our greed and our desire for more stuff and more money and more prestige, and our competitive urges are just over-exaggerated. [A] culture like that will go extinct.”
If modern humans don’t change our ways to find harmony with the Earth, Gaia will do it for us.
“We’ve pushed nature back, we’ve destroyed her to such an extent that there have to be very powerful feedbacks to control this species, the species of modernity."
“That's a classic Gaian feedback,” Harding says. “We’ve pushed nature back, we’ve destroyed her to such an extent that there have to be very powerful feedbacks to control this species, the species of modernity. I won't say humans because humans are wonderful. It’s modernity that's the problem. I've come to that conclusion. Modernity, this modern way of life, it’s a big problem. And it's evoking these feedbacks from Gaia. The coronavirus is just the start. If we don't do anything about greenhouse gases and the destruction of biodiversity, which helps us control greenhouse gases, amongst other things, we haven't got much hope, really, not in the long-term. That's the science.”
Perhaps the most powerful observations of Gaia come from people who have seen Earth from outer space, including retired NASA astronaut Ron Garan, who flew in the space shuttle and got to take a spacewalk.
“I had, obviously, never seen the Earth from that vantage point,” he says. “And I thought about that, when we…look at the Grand Canyon…when we sit on a beach at sunset and look at a beautiful sunset, gravity is pushing us into that scene. We’re inside the frame of the masterpiece, we're part of that painting, if you will. But for the first time in my life, I was seeing this exquisite beauty from the outside. And somehow that outsider perspective — what I call the orbital perspective — compelled me to feel deeply interconnected with everybody and everything on the planet.”
Garan says the name Gaia is fine but he balks at the word hypothesis.
“I don't think it's a hypothesis, I think it's obvious,” he says.
“Seeing the planet from that vantage point of space makes it obvious that we're looking at a living, breathing organism, a multicelled organism, an organism that has different aspects of it, based on the various, multivaried species of life that exists upon the surface and below the surface of Earth and in the atmosphere of Earth. And all of those different species, different individual animals and plants are all part of an implicit wholeness that is the planet itself. It's all not only interconnected, it's deeply, deeply interdependent.”