I've been on a book bender this summer. One topic I've been devouring and relearning has been the Gaia Hypothesis, the idea that life controls (to some extent) the environment in which it occupies in while also being influenced by the environment. The term "Biosphere" was actually coined by the first paper opposing the hypothesis back in the 1970s. Nowadays, the biosphere (all lifeforms and ecosystems) is recognized as its own system that interacts with the inorganic systems of the Earth, from rocks to water and air, under the scientific field known as "geophysiology".
The extent of that interaction is what the Gaia Hypothesis tries to answer. How does the biosphere interact with other systems? Is life a mere passenger, a worker, or the captain of our pale blue dot?
Some basics below, and more following the fold. And if y'all like this, maybe a series.
The Gaia hypothesis, also known as Gaia theory or Gaia principle, proposes that organisms interact with their inorganic surroundings on Earth to form a self-regulating, complex system that contributes to maintaining the conditions for life on the planet. Topics of interest include how the biosphere and the evolution of life forms affect the stability of global temperature, ocean salinity, oxygen in the atmosphere and other environmental variables that affect the habitability of Earth.The hypothesis (now accepted as theory by some), was thought up by James Lovelock, an English chemist and earth scientist, when he worked in the early days of NASA's Jet Propulsion Laboratory in CA. In 1957, Lovelock invented the electron capture detector, which determines the composition of gases in a sample to within parts per trillion (ppt). At that level, Lovelock was able to find traces of pesticides in Antarctic penguins and CFCs in the middle of the ocean, both far from their respective sources.
The second contributor to the hypothesis was the late microbiologist Lynn Margulis, founder of the endosymbiotic theory. She helped to flesh out the hypothesis by noting that microbial life has been on Earth for most of its existence (~4 billion yrs for single cells to multicellular's 1.5 billion) and influences the lithosphere, hydrosphere, and atmosphere. Microbes were responsible for oxygenating the air 2.4 billion yrs ago, replacing our methane and CO2 heavy atmosphere into the surprisingly stable amount of ~21% oxygen since.
Now that we got some basics, I'll go into some of the concepts of Gaia: homeostasis, Daisy World and feed back loops.
Homeostasis - The wisdom of the body
If you get a cut on your hand, your body pretty much knows what to do to heal itself. Platelets start clotting the wound, skin cells divide to make scar and repair tissue while white blood cells patrol the area just in case of infection.
A whole slew of bodily functions just happen automatically. The liver can repair and heal itself, kidneys keep a proper balance of salts in the body, fat cells migrate to where they are needed all without you thinking about it. Systems in the body do their best to keep a balance around a set point or repeated function in the absence of outside pressure or stress. Just like the body, organisms in an ecosystem can help to maintain homeostasis.
Trees in the Amazon Rainforest have been shown to have a dramatic influence on cloud and rain development, which obviously contributes to creating and sustaining a rain forest. Some new research from the Max Planck Institute for Chemistry reveals interesting detail on how that works and how the forest is essentially a self-contained cloud-producing biogeochemcial reactor. It all comes down to miniscule organic particles in the air, produced by plants and fungi.
More than 80% of supermicron particles, which have a diameter of more than a micrometer, are made up of primary biological aerosol material, such as fungal spores, pollen and plant debris, and are directly released into the air from the rainforest. They serve as ice nuclei and are very important for the evolution of precipitation.An ecosystem like the Amazon releases thousands of different Volatile Organic Compounds (VOCs) every day — they're responsible for its rich smell. When VOCs loft into the atmosphere, they breakdown, become oxidized or react with other chemicals. The gases then condense and freeze, forming ice crystals kicking off cloud formation and eventually rainfall further down the forest. The system repeats again and again with all the fungi and plant life acting as a biological pump, moving water from the Andes mountains to the Amazon River delta.
The fact that aerosols above the Amazon rainforest are nearly completely of biogenic origin tells the scientists a lot about the ecosystem. "The Brazilian rainforest during the rainy season can be described as a bioreactor", says Ulrich Pöschl, who played a leading part in the study. Water vapour rises from the forest, compensating on aerosols. These are then transported up to a height of 18 kilometres. Water droplets and ice crystals grow in the clouds thus formed until they fall to the ground again as precipitation. Part of the precipitation evaporates and the rest irrigates the Amazon flora. The plants, while growing, continue to release organic material into the atmosphere, on which new clouds grow.
In this case, homeostasis helps to perpetuate the system. Homeostasis can also help recovery after a trauma.
Think of a forest fire. While traumatic, if the forest was overall healthy and the event wasn't too significant, most of the environment can be reestablished. After the burn, recovery begins with small plants like grasses. Shrubs and bushes pop up later, giving way to small trees and pines. During each stage of development, the forest replenishes nutrients lost in the fire through the buildup of organic matter. Eventually, fully mature trees can make a living on the previously burnt area and re-establishing homeostasis for the area, the same way your liver repairs itself after a night of heavy drinking.
Currently, the Earth has a ~21% oxygen, while early Earth, Venus and Mars have essentially none as shown below.
Under the Gaia hypothesis, the biosphere functions as a vast superorganism that actively modifies and maintains its planetary environment to produce the environmental conditions necessary for its own survival. A good way to prove this concept was through the Daisy World.
Daisy World - Flower Power
My first exposure to the Gaia Hypothesis was in 1992. It came via the Super Nintendo game, SimEarth. One of the modes in the game was "Daisy World", a mathematical model demonstrating life maintaining a stable temperature on a planet despite the parent star's increasing light and heat.
Some explanation on that last point; Our sun, like all Main-Sequence stars, was dimmer and cooler when it first formed, probably only ~2/3 as bright as now. Towards the end of our sun's life (~4.5 billion years from now), it will be ~50% brighter than now. For most stars, as they age, they get brighter and burn hotter.
Given that info on star development, the first Daisyworld models were based on the following:
-The parent star is steadily increasing the heat and light it gives off.
-Once a minimum temperature is reached, life develops. Life will also die after a maximum temperature is attained.
-The life available: white and black daisies.
-White ones reflect most light and heat while black does the opposite.
-Flowers grow best at a certain "optimum" temperature.
Initial runs of the model produced graphs like the one below:
On the bottom graph, the brown line shows the planet's temperature without daisies, while the pink shows planet temperature with daisies. Comparing the two graphs, you can see how the temperature fluctuates a little over a long period of time in the presence of flowers. The daisies regulated the temperature like a thermostat, maintaining a small range around 22 C. This homeostasis continued despite changing populations and increased energy from the star.
Later models of Daisy World have included different shades and species of plants, herbivores and carnivores. Lovelock, in The Ages of Gaia, noted that in one model he had 30 colored plants, 12 herbivores, and 3 carnivores. In this model, the biodiversity was greatest at median/comfortable temperatures and was quite low at the cold and hot temperatures. Interestingly, the more biodiverse a Daisy World is, the longer it can stay alive (before being cooked by the star) and the better it was able to handle and recover from extinction events.
Daisy World also demonstrates how the basic interaction between different feed back loops help to influence the environment. Black daisies are positive feedbacks, while white flowers created a negative feedback.
Feedback Loops - Negative and Positive
In the Daisy World model, black daisies absorbed sunlight, creating heat. Initially, this heat helped to raise local temperature to allow more black daisies to grow. This is a positive feedback, and was useful, up until a certain point. White daisies popped up to offset the warming from the black daisies, cooling the planet and providing a negative feedback, until the system broke.
In the human body, sweating to cool off would be a negative feedback, cooling off a heated body to stabilize around the usual homeostasis point. Exercise can induce a positive feedback in that as muscles grow, fat cells are relocated to provide more energy for the muscles. The more energetic muscles can operate better, thus creating a higher demand for fat cells in and near muscles, which then make the muscles more energetic. This can also be termed a "virtuous cycle", since gaining muscle mass/losing fat is desirable.
The Arctic Ice Cap "Death Spiral" (aka "Vicious Cycle") is also a positive feedback loop. As more ice is lost, more water is exposed. Water absorbs more heat than ice, thus increasing the temperature, hindering ice development and so on.
Studying the involvement of life in cycles of the atmosphere, hydrosphere and lithosphere cycles is where a lot of work on the Gaia Hypothesis has been associated with.
Lynn Margulis and other microbiologists have shown that oceanic plankton has an influence on cloud formation and reflectivity, which in turn, influences global temperature.
One area of scrutiny is the plankton-cloud relationship. Scientists had long known that plankton exude dimethylsulfide, or DMS, which diffuses into the atmosphere. But in 1987, Robert J. Charlson, an atmospheric chemist at the University of Washington in Seattle, and his colleagues proposed that DMS, when exposed to air, forms sulfate particles around which water condenses. The clouds cool the earth. More recently, others showed a correlation between DMS levels and the brightness of clouds over the Southern Hemisphere. Still, no one has shown that plankton and marine clouds work in concert to keep temperatures stable. It may take years to quantify the relationship between plankton, atmospheric conditions, temperature and the amount of light that clouds reflect but, as Margulis likes to say, the mechanisms of Darwinian evolution haven't been proved yet either.In some cases, a natural cycle can become stronger to try to counter a change. Note the chart below.
[T]he teeth in that saw-tooth pattern have grown bigger over the past 50 years.In this feedback loop, plants are responding to higher CO2 levels by increased growth, which in turn removes CO2 from the air. When you get sick, your white blood cells ramp up activity to produce antibodies and other defenses, trying to fight off the infection. If the infection overwhelms the body's feedback systems, death is likely.
"The vegetation is taking deeper breaths, if you will," Graven says.
In particular, that is happening in the far northern parts of the planet, mostly the boreal forest and the Arctic tundra. And Graven says you can actually see changes in the vegetation from space and in aerial photographs.
"The area covered by forest in these northern latitudes has grown over the past few decades, so there's more forests," she says. "We've also seen that some species and ecosystems have been migrating pole-ward," she says.
Under The Gaia Hypothesis, think of the Earth as a living thing. Rainforests are like the lungs, ocean currents resemble a circulatory system, while plants and animals are like microbes in the human gut. Each part seems to operate independently from one another, but are connected in unimaginable ways.
The Earth has been through a lot. Cosmic radiation, countless asteroid impacts, mega-volcanoes and climatic upheavals. Life bounced back from all those events, usually stronger and more diverse than before. Currently, Earth has to deal with humanity, which is currently disrupting many feedback systems. Eventually, a breaking point will be reached. Earth will continue beyond that point, but will humans continue as well?