The Gaia Hypothesis

If you left Earth on a long spaceflight out into the universe because it was too lonely a thought to think that Earth was the only harbor of life in the universe, how would you search for it?  How would you recognize it?  What tools and perspectives would you take with you to help you find it?  Would you expect to find plants and animals just like here somewhere else?  Would you take a microscope and look for microbes because they are the hardiest and most survivable organisms known to us?  Would you only search for Earth-like planets with water and mild climates?  Would you look for massive societies that have changed the whole landscape of their planets?  Would you expect to pass someone wandering through space looking for life just like you?  Could you recognize it if you saw it at all?  Do we even recognize all the lifeforms that exist on Earth or are there still lifeforms that are commonplace, but unsuspecting--like a rock perhaps--because we lack the definition, perspective or technology to identify it?  Are viruses alive?  Modern science doesn't think so (still hotly debated) even though viruses reproduce.......in a way, metabolize..........in a way, and have bodies.........in a way.

You might realize by now that there's a glitch and that is that life is difficult to define.  Most definitions of life have an obvious bias, and that is that humans define as life what is most human-like and the further away the resemblance becomes the more leery people become to bestow the title of "life."  James Lovelock, an independent scientist and subject of this blog, pointed out something interesting by noting how we all must have some kind of instinctual life-finding mechanism.  It helps us survive if we know that something is alive and what kind of life it is.  Is it edible, dangerous, diseased, friendly, sexy, useful, etc.?  But our life-finding instinctual program isn’t infallible, up to the late 1800’s people thought yeast was a mere chemical catalyst that fermented sugar to alcohol.  We now know that yeast is a living organism that eats sugar and excretes alcohol as a waste product. 

James Lovelock was working for NASA in the 1960’s and 1970’s when he got the project to design a method of life detection for the space probes that were to be sent to Mars and elsewhere in the solar system.  He was an atmospheric scientist by training, but he had a vast interest in and knowledge of many subjects which he called upon to come up with a simple, but rather revolutionary idea.  His neighbor proposed the name Gaia, after the Greek God for Mother Earth, for the idea and it has appropriately become known as ‘The Gaia Hypothesis’ ever since.

The Gaia Hypothesis in aphorism form might go like, ‘if you want to find life, look for paradoxes.’  If you see a volatile atmosphere that maintains an equilibrium of volatile compounds without reacting to an inert state….life must be there maintaining the tense equilibrium.

An example…….

 

If we agree for the sake of making a point that a ladder is a non-living object and that a human being is alive we can try an experiment that involves a tightrope between skyscrapers!  If James Lovelock were to prove to you (albeit in a grossly over-simplified way) with The Gaia Hypothesis that a human is alive and that the ladder is non-living, he might try to balance the ladder with its two feet on a tightrope and point out that even when it is balanced and stays standing the slightest disturbance will topple it.  It can’t adjust itself to the improbable circumstance of staying balanced on a tightrope for long.  Whereas, not only can a human being be balanced and stay balanced on a tightrope between skyscrapers, but a human can also adjust to wind, sun and rain (and fear!) while purposefully walking the distance to safety.

The point to James Lovelock is that both a ladder, tall and skinny on two feet, and a human, tall and skinny with two peg legs, have a similarly, unstable shape and one would predict that neither would stay balanced for long on the wire.  Yet the ladder topples as one would predict whereas the human (albeit a highly skilled human), against predictions, stays standing and moves about with a self-regulating sense of balance.  Life, to James Lovelock, maintains by self-regulation a kind of intensity, an improbable equilibrium, against the forces of entropy that want to take all high-energy systems to their lowest and most stable state (planted in the pavement below).

Of course, James Lovelock, didn’t propose a tightrope walking proof to the scientific community when presenting his theory.  Rather he relied upon his scientific expertise and showed the insight he’d had while considering the atmospheric chemistry of Earth itself.  Before the Gaia Hypothesis meteorologists, geologists and chemists had explained the constant levels of the different atmospheric gases as the result of inorganic processes.  For example, the 21% oxygen content of the atmosphere was accounted for by the breakdown of oceanic water by sunlight into hydrogen gas (which mostly escapes into space) and oxygen gas.  When Lovelock examined this process closer he realized that for the amount of methane produced by living organisms (which readily reacts with oxygen in sunlight producing water and carbon dioxide) there was no way that the current levels of atmospheric oxygen could remain as high as they are; there had to be another source or process that was keeping atmospheric oxygen as high as it is.  Similarly, he looked at many of the gases that compose the atmosphere at constant levels and realized that the atmosphere is too volatile a place for inorganic processes to be regulating it.  If it were controlled by inorganic processes alone he believed that the atmosphere should be nearly 98% carbon dioxide and all other gases should only occur in trace amounts; but in fact, carbon dioxide is only at a current level of .03%.  It was facts like these that led James Lovelock to propose that life itself was regulating the composition of the atmosphere and that in fact the Earth itself could be seen as a kind of living entity where all organisms are collectively contributing to the stabilization of the environment.

Lovelock points out that despite variations in the climate of Earth over time (including hot periods and ice ages) that the environment has always been hospitable for life, as proven by the unbroken, 4 billion year long fossil record.  And not only has it been hospitable, but it has also allowed for an unbroken trend towards ever more organized levels of complex lifeforms.  He continues that it is safe to predict from scientific knowledge that the sun’s output, combined with geologic factors from Earth's past, has varied greatly enough in that time period that the oceans of the Earth should have completely frozen in some geologic eras and boiled mostly away during others, but the fossil record proves that this has never happened and that life has inhabited the oceans the whole 4 billion years.  This, he argues, is further proof of Gaia (that, collectively, life is regulating the climate on Earth to be hospitable for life).

A clarifying example would be the way we regulate our body temperature.  If we were dead we’d expect that our body temperature would passively match the environment’s temperature, but if we’re living, self-regulating and Gaia-like then we’d expect that our body temperature would stay steady no matter if the environment’s temperature were 40 degrees Fahrenheit or 110 degrees Fahrenheit.  Our body heat is very Gaia-like because it maintains the improbable equilibrium (considering how small we are compared to the forces of the surrounding environment) of 98.6 degrees Fahrenheit.  It is just these improbable equilibriums that one should be looking for when searching for life in the universe, according to Lovelock.

Gaia is about a collective, yet unconscious mutual effort to survive in which all organisms from whales to viruses, redwoods to spiders, lizards to humans, participate in regulating the planet’s atmosphere, oceans and land by offsetting each other’s negative impacts to keep Earth habitable.  By James Lovelock’s estimation all living things change their environment to meet their needs and all things “pollute” as a result of their activities.  Evolution is a process by which Gaia is maintained and the environment, rather than being overwhelmed by the pollution of certain organism’s activities (like humans for example), remains habitable as organisms evolve to offset the effects of others.  It’s all about cycles, balance and symbiosis.

Lovelock makes a philosophical argument to meld The Gaia Hypothesis into a coherent theory by explaining how organisms come to participate in the life-regulated Earth.  He asks if it’s unreasonable to suppose that by some instinct/disposition we might derive pleasure from seeing a beautiful, healthy environment.  If we do have such an "aesthetic sense" for our environment then it follows that we may be instinctually programmed to recognize our optimal role in relation to the life around us and thus derive pleasure from pursuing that harmony.

Perhaps James Lovelock paints too rosy a picture of life and the relationships it has amongst its members and the environment though, in truth, he has quite cynical opinions about the prospects for humanity.  The Gaia Hypothesis has been heavily criticized by orthodox scientists, but the volume of criticism has toned down since he proposed a mathematical model about how Gaia might work called Daisyworld.  Only time and further scientific evidence will determine what parts of The Gaia Hypothesis are correct and what parts are mere wishful thinking.  Regardless of outcomes, it is an influential idea of our time and an interesting one at that. 

Watch a Video

A recent measurement of the annual fluctuations of carbon dioxide gas in the atmosphere has been measured by a NASA satellite orbiting the Earth.  It actually affirms The Gaia Hypothesis because it shows that carbon dioxide, a greenhouse gas, naturally builds up in the atmosphere during the winter, helping keep Earth warm enough for life to survive, and gets removed from the atmosphere in the process of photosynthesis throughout the spring and summer to keep the Earth cool enough for life.  (By contrast, our orbiting moon, without an atmosphere at all has temperature fluctuations from 225 degrees Fahrenheit during daytime to -243 degrees Fahrenheit by night!)  Click the below link to see Earth "breathe".  The global fluctuations of carbon dioxide are shown about half way through the video. 

http://www.youtube.com/watch?v=YcxS2LoZukQ

-Seth Commichaux

The Carbon Cycle

 

Carbon can be found in elemental form in nature as an amorphous solid, graphite, fullerene or diamond.  Overall, carbon is the 6th most abundant element in the universe and constitutes 22.85% of the human body.  Over 10 million compounds of carbon have been synthesized in the laboratory and many thousands, if not many millions, are found in nature which attests to the tremendous versatility of the element (a quality that lends to the great versatility and diversity of life itself).  Because Earth is dynamic, carbon, like all elements, gets cycled through the environment and life plays a major role in this process.

 

The major reservoirs of carbon vastly overshadow what is biologically cycled and are fairly stable in ocean sediments and terrestrial rock.  Fossil fuel deposits are also a major reservoir @ 4,000 metric billion tons, but we are adding about 9 billion metric tons of its carbon to the atmosphere through combustion and other emissions each year.  The atmosphere's carbon, mostly in the form of CO₂, is the most rapidly cycled.  Atmospheric carbon has risen from 578 billion metric tons (as of 1700) to 766 billion metric tons (as of 1999) due to human emissions.  Life's total biomass carbon accounts for, approximately, a 1,000 billion metric tons (though it is potentially much higher depending on how many microorganisms there are on Earth, which is hard to estimate). 

Sink	Amount in Billions of Metric Tons
Atmosphere	578 (as of 1700) - 766 (as of 1999)
Soil Organic Matter	1500 to 1600
Ocean	38,000 to 40,000
Marine Sediments and Sedimentary Rocks	66,000,000 to 100,000,000
Terrestrial Plants	540 to 610
Fossil Fuel Deposits	4000

Estimates of Carbon Reservoirs

Though the major reservoirs of carbon are inorganic sources, they don't cycle substantially and are quite stable over geologic time.  The carbon that does actively cycle is almost entirely a biological affair.  On Earth the carbon cycle is one of the most essential for life because all life that we know about is made of proteins, lipids, carbohydrates and nucleic acids (all carbon based molecules).  To give a feel of the rate of turnover we're talking about here, the average carbon dioxide (CO₂) molecule gets cycled through the biosphere approximately once every 300 years.  (Something interesting to think about:  The molecules of our bodies have a turnover rate as well.  Every time you eat something your body incorporates new molecules and lets old molecules leave the body.  It's like having an old brick building that needs repairs.  So you get new bricks to replace the old, corroding bricks.  By swapping out the old bricks with new ones you are changing what the building is made of, but the building's shape and structure remain the same.  It's interesting that we feel like the same person from day-to-day even though our molecules are being replaced all the time!) 

  

We'll begin the cycle with the carbon fixers or primary producers who are the plants, algae, cyanobacteria, green bacteria, and purple bacteria.  The cycling activities of these organisms largely determines the potential productivity that an ecosystem can support.  Their main service is to take inorganic CO₂ and convert it into organic carbohydrates, lipids, proteins and nucleic acids that all other lifeforms require to get the energy and nutrition they need.  They play the essential role of introducing otherwise inaccessible forms of carbon into the food web.  Mostly this is done by photosynthesis, a remarkable process that converts sunlight into energy-rich molecules like sugars (Over 150 billion tons of dry organic matter is produced by photosynthesis each year!).  Other methods employed by microorganisms also convert inert CO₂ into organic matter such as methanogenesis (reduction of carbon dioxide to methane) and acetogenesis (reacting carbon dioxide to acetic acid).  These processes require no light, but do require special molecules, metabolic pathways and enzymes.  The special benefit of photosynthesis, if you appreciate breathing, is the byproduct oxygen.


  



Once inorganic carbon has been made into organic compounds the cycle is completed by consumers (like humans) and decomposers who, essentially, break down the organic compounds to carbon dioxide and water through respiration and fermentation.  Respiration uses oxygen to breakdown molecules, while fermentation breaks down organic compounds without oxygen.  Respiration is an interesting process because it is, in essence, a cell's version of an internal combustion engine minus the flame, releasing energy in a slower and more efficient manner than small explosions (like in an engine).

Decomposers play a rather under-appreciated, yet essential, role.  Imagine a world where things consumed, died and bodies piled up, but never decayed.  After a while Earth would be a ball of corpses with all the nutrients locked up in bodies.  Thankfully decomposers exist and return lifeforms to their fundamental elements!

Microbial decomposers are also able to break down plant polymers like lignin (wood) and cellulose (the most abundant biopolymer in the world) that no one else can digest.  They exist in the environment and also in the guts of termites and ruminants (cows, sheep, deer, goats, giraffes, camels, etc.) where they break down these polymers to their component sugars which animals can digest.  Without this special ability plant matter would accumulate and remain, mostly, unusable.

DISCUSSION

So now that we've taken a dose of science what is the take-home-message?  What can the carbon cycle teach us about life on Earth?

..............One organism's poo, is another organism's food..............

Perhaps a little too crude, but it captures the essence.  Life is like a wheel of complementary colors.  Diversity is the key because in the process of growing, digesting, regenerating, transforming and just living and dying in general, one organism requires another organism(s) that offsets their effects so that Earth can maintain some kind of balance.  If animals breathed and there were no photosynthesizers, eventually, we'd all suffocate in our own carbon dioxide.  Similarly, if plants converted all the carbon dioxide to oxygen, they'd suffocate too.  We need each other, we need diversity, to survive because being alive means producing waste.  If your environment is healthy and diverse there's bound to be some organism out there that can use your "trash" and transform it back into something usable for you.  To complete the cycle we help other organisms by putting to good use their waste returning it to an accessible form for them.  Think of cheese, yogurt, bread, soy sauce, pickled vegetables, alcoholic beverages, and all the other "waste products" of microorganisms that we eat as delicacies.  In reality, we're just participating in the carbon cycle.  

Sources:

http://www.eoearth.org/article/Carbon
http://en.wikipedia.org/wiki/Compounds_of_carbon
http://www.physicalgeography.net/fundamentals/9r.html
Microbial Ecology: Fundamentals and Applications, 4th ed by Ronald M. Atlas & Richard Bartha

-Seth Commichaux 

Fruit Flies Need Medicine Too

Ever had childbirth pains or an eye infection?  Greek physician Hippocrates (still remembered by the Hippocratic oath of doctors to do no harm), in 400 BCE, would’ve prescribed you to chew on willow bark.  I don’t know about you, but when I have an eye infection (being unfamiliar with childbirth pains) one of the last things I contemplate doing is gnawing bark off trees.  But sure enough, in 1883 chemists working at the Bayer division of I.G. Farben in Germany synthesized a derivative of the active ingredient in willow bark called acetylsalicylic acid and called it aspirin, a very effective reliever of pain, inflammation and fever—as evidenced by the 80 billion tablets consumed each year in the United States alone! 

ASPIRIN

Whereever on planet Earth people have found themselves they’ve come up with remedies and rituals to cure diseases and other health problems.  Science has debunked many of these and few have proven effective against especially aggressive diseases such as small pox, but some have been upheld as legitimately effective treatments for various ailments.  The question that comes to my mind is how did the people know or come to figure out these medicines from the plants, animals, and minerals in the vastly diverse ecosystems of Earth that they found themselves in?  Was it a matter of trial-and-error/experimentation?  Was it an I’m-going-to-die-anyway moment and anything was worth trying?  Did they observe and mimic animals?  Was instinct/evolution a guide? Intuition or dreams?  Can you use your senses and determine what will help you by taste, touch, sight, smell, etc?  Is it a combination of these things or some other reason? 

I know of no answer to many of these questions, but an interesting clue comes from the non-human realm that points to an ancient, evolutionary origin of medication.  In essence proving that humans did not invent medicine, but rather inherited a tendency that we have vastly expanded and improved upon with our technologies. 

Evolutionarily speaking it seems that, to survive, many organisms, including humans, have had to supplement their innate immune systems with medications in order to survive the onslaught of pathogens and injuries that one inevitably encounters in a lifetime.  The fact that other organisms use medicine and that we use medicine implicates an interesting, interconnected history for this phenomena.  Now, what is the evidence that this link exists between us and the rest of the living world? 

There are many examples of medication in the biosphere: from chimpanzees who eat leaves not normally part of their diet to kill nematode parasites, to ants and bees who lacquer their homes with anti-microbial/anti-parasitic resins when the colony becomes infected to just name a few.  I am going to focus on one specific example to give you a feel for the complexity of the behaviors involved.

Drosophila melanogaster, Fruit Fly

The example concerns a famous mainstay of scientific study, the common fruit fly, Drosophila melanogaster, commonly found buzzing around a house near you.  The fly larvae eat the fungi and bacteria that cause fruit to rot and ferment when overripe.  They have a certain resistance to the toxic effects of alcohol which is a good thing because levels can range from 5-15% in the rotting fruit where they are growing.  But there is another reason for this alcohol tolerance and it is that fruit fly larvae are parasitized by wasps who lay their eggs inside the fly larvae with an injection of venom to suppress their immune systems so that the wasp offspring can grow, eating up the fly larvae from the inside out, eventually, killing them.  Alcohol is a toxin to many of the wasps who parasitize the flies.  The unlucky wasps developing inside of the alcohol-consuming fly larvae die a horrible death where their internal organs liquify and get ejected out of their anuses. 

That fruit fly larvae live in an alcohol-rich environment that kills wasps is not proof of medicating behavior however.  What makes fruit flies an example of a species that medicates itself is that alcohol in the concentrations to kill developing wasps is toxic to the fly larvae as well after long enough durations and so must be done in response to being parasitized, not on a consistent basis. 

In fact, the flies can choose food for their offspring that minimizes the impacts of disease (in this case, being parasitized by the wasps) when the need arises.  Also, the fruit fly larvae can adjust their diet and environment to increase their blood alcohol levels when developing wasps are in their bodies. 

When adult fruit flies sense parasitic wasps in their environment they can anticipate the infection risk for their children.  They respond by medicating their offspring, putting them in an alcohol-rich environment.  Surprisingly, the flies can identify the wasps by sight alone and can distinguish between male and female wasps, as well as parasitizing wasps versus non-parasitizing wasps.  If the fruit fly parent sees a male wasp or a non-parasitizing species of wasp they will not seek out high alcohol environments for their offspring to grow in, only detection of nearby female wasps of parasitizing species consistently elicit the medicating behavior. 

Similarly, the larvae also know when they've been infected by the wasp eggs and will move to an environment with higher concentrations of alcohol and will begin eating food with higher concentrations of alcohol in an effort to rid themselves of the parasites in their bodies. 

Medicating behavior similar to the fruit flies' is being found more and more in the insect world.  Monarch butterflies infected by parasites, for example, will lay their eggs on plants with anti-parasitic chemicals which drastically reduce the levels of infection in their offspring.  Somehow they recognize that they are infected and they take action to save the next generation.

Monarch Butterfly

The researchers who amassed the information on fruit fly medication that I’ve been talking about pointed to the potential that alcohol might prove effective in treating parasitic diseases in humans, something not previously researched. 

CONCLUSION 

We humans often fancy ourselves superior to all other living things and point to our sophisticated gadgets and life-lengthening medical technologies to prove our grander intelligence, but as researchers worldwide are beginning to discover......perhaps humans are not so many heads higher than the rest of the biosphere after all.  Many of the behaviors, including medication, that we've traditionally classified as uniquely human, may just be evolutionary tendencies that we've inherited alongside many other organisms. 

Perhaps another message to derive from the example of the fruit fly is one of respect, for it appears that even something as apparently lowly and simple as a fruit fly might have something to teach us about what it means to be human.  

Sources Cited:

http://www.sciencedaily.com/releases/2013/02/130222102958.htm
http://www.sciencedaily.com/releases/2012/02/120216133436.htm

Neil F. Milan, Balint Z. Kacsoh, Todd A. Schlenke. Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly. Current Biology, 2012; DOI: 10.1016/j.cub.2012.01.045     

B. Z. Kacsoh, Z. R. Lynch, N. T. Mortimer, T. A. Schlenke. Fruit Flies Medicate Offspring After Seeing Parasites. Science, 2013; 339 (6122): 947 DOI: 10.1126/science.1229625

-Seth Commichaux