The Breathing Earth

by Richard R. Hofstetter, Esq.

Human activities may well be changing the Earth's climate; a principal culprit is carbon dioxide, released upon the combustion of fossil fuels.

CO2 is, of course, naturally present in the Earth's atmosphere, albeit in relatively small quantities. Its scarcity belies its importance: it makes plant life possible. But it is possible to have too much of a good thing. In larger concentrations, CO2 is poisonous to animal life. It is also very efficient at absorbing infrared radiation which would otherwise be reflected back out into space. As CO2 and other so-called greenhouse gasses accumulate in the atmosphere as a result of human activity, the predictions of global warming no longer seem alarmist. Our sister planet Venus has an atmosphere that is composed largely of CO2, and, consequently, has surface temperatures high enough to melt lead.

Prior to the industrial revolution, the level of atmospheric CO2 stood at less than 300 parts per million. Today, our air contains approximately 375 parts per million. In fifty years, it will rise to more than 700 parts per million. This unprecedented rise is the result of the cumulative assaults on the planet's air by human exhaust pipes and slash and burn agriculture. Some scientists believe that the observable rise in surface temperatures worldwide is the result of such global warming. Their warnings of pernicious Malthusian-like consequences for our race (the "final solution to the world's CO2 question") may not be unfounded.

The so-called carbon cycle can best be understood as breathing by the planet Earth. Each year, green plants inhale about 100 billion tons of CO2 from the atmosphere during photosynthesis. Animals and other organisms which break down plant matter (ex: fungi, molds, bacteria, microbes, termites, worms, beetles, slugs, et cetera) exhale about 100 billion tons annually back into the atmosphere. Since the atmosphere at any given time holds about 700 billion tons of CO2, all of Earth's CO2 is recycled in this fashion about every seven years.

There are other, non-biological, sources of CO2, such as volcanic activity and the burning of vegetation. However, in the long run these sources represent only minor perturbations in the cycle of respiration. Over eons, the planet can remain comfortably cool if only as little as a half billion tons of CO2 is permanently buried each year, representing about one part per thousand of that which exists naturally. We know that a phenomenal amount of carbon has already been sequestered as a result of biological activity. The vast stores of hydrocarbons underfoot, that we now extract and burn for fuel, came from the soft tissues of herbaceous plants that grew millions of years ago, and would most certainly remained entombed forever were it not for human activity. Limestone and marble are nothing more than the products of geological forces acting upon the carbonate-bearing shells of organisms which perished eons ago. Even sea water can capture and hold carbon (CO2 and water are in equilibrium with carbonic acid and its anion in solution: CO2 + H20 = HCO3). The world's oceans hold nearly fifty times as much CO2 in this form as the atmosphere. In the absence of life, CO2 would be the most abundant gas in the Earth's atmosphere.

We humans have upset Earth's breathing. Each year, we add an extra six billion tons of CO2 to the air. We've given the planet a case of asthma. Our fear is that Earth may soon be developing a fever, along with her asthma.

Or perhaps the Earth will just change the way she breathes.

Is it reasonable to assume that the six billion extra tons of carbon will just accumulate in the atmosphere ad infinitum, until our race perishes in the ovens of a Bio-belzek? Or would it be logical to expect the rate of photosynthesis, and carbon burial, to increase and mitigate the effect?

Recent observations would suggest the latter. Though the level of CO2 is unquestionably on the rise, it is not accumulating in the air quite as fast as we would otherwise expect. Some of the carbon is missing.

In the 1960's, NASA hired Lovelock to devise an experiment for detecting the past or present existence of life on Mars. His assignment forced him to consider the means by which one could detect the existence of life on Earth. As an atmospheric chemist, Lovelock, logically, first studied the Earth's atmosphere.

Free oxygen, scientists agree, is the product of biological activity. Oxygen is also very reactive, and readily combines with other elements to form oxide compounds. Accordingly, it must be constantly replenished, or it will gradually disappear.

Oxygen is also necessary for much of the life on this planet. Humans and virtually all other animals would quickly suffocate without it. About 21% of the Earth's atmosphere is comprised of oxygen. From the best information available to us, oxygen has remained at or near 21% for a considerable period of time.

The mere presence of more than a trace of elemental oxygen in the Earth's atmosphere is evidence of the existence of life. The presence of a significant amount of oxygen on Mars would therefore be a signature of life (or at least life as we know it).

But Lovelock became intrigued by a more basic question: how and why is oxygen, a highly reactive biologically produced element, held at a constant 21% in the Earth's atmosphere? The chance of this occurring randomly is virtually zero. Lovelock then observed another remarkable fact that further belied any notion that this could be mere coincidence: the figure of 21% is exactly the concentration of oxygen which is most conducive to the survival of life on the planet (at least, life as it currently exists). If the percentage of atmospheric oxygen was higher than this figure, much of the Earth's biomass would be combustible. If it was lower by even a few percentage points, most present animal life would suffer or even die.

Lovelock summarizes these concerns:

Life first appeared on the Earth about 3,500 million years ago. From that time until now, the presence of fossils shows that the Earth's climate has changed very little. Yet the output of heat from the sun, the surface properties of the Earth, and the composition of the atmosphere have almost certainly varied greatly over the same period.

The chemical composition of the atmosphere bears no relation to the expectations of steady-state chemical equilibrium. The presence of methane, nitrous oxide, and even nitrogen in our present oxidizing atmosphere represents violation of the rules of chemistry to be measured in tens of orders of magnitude. Disequilibria on this scale suggest that the atmosphere is not merely a biological product, but more probably a biological construction: not living, but like a cat's fur, a bird's feathers, or the paper of a wasp's nest, an extension of a living system designed to maintain a chosen environment. Thus the atmospheric concentration of gasses such as oxygen and ammonia is found to be kept at an optimum value from which even small departures could have disastrous consequences for life.

The climate and the chemical properties of the Earth now and throughout its history seem always to have been optimal for life. For this to have happened by chance is as unlikely as to survive unscathed a drive blindfold through rush-hour traffic.

-- Gaia: A New Look at Life on the Earth

Early life had to cope with a reducing atmosphere, rich in hydrogen and hydrogen-bearing molecules but bereft of oxygen. The first life forms could have generated a chemical gradient as large as plants do today, with hydrogen-rich material being found externally, rather than internally. Over time, the abundance of life of this kind would have oxidized the reducing materials in the Earth's crust, leading to a build-up of oxygen in the air.

Atmospheric oxygen must have been very poisonous to most of these early life forms, much as it is for today's anaerobic bacteria. But Gaia adapted. Rather than oxygen being catastrophic for life, life has since become dependent upon it. Today's oxygen-breathing animals owe their very existence to cynaobacteria (sometimes called blue-green algae) that polluted the atmosphere with oxygen aeons ago. (Even today, the fossilized microbial mats of these early polluters, known as stromatolites, still grow in a few scattered subtidal marine localities.) The Earth we see today is at Gaian homeostasis, an improbable entropy sustained this way by the world's most ancient life form.

One can imagine how Gaia could respond to various changes in the contemporary world. As CO2 rises above the optimal level for life, it would seem that the added nutrient would be exploited by plants everywhere, and the rate of carbon fixation (and ultimately carbon burial) would rise accordingly.

Boyd Strain, a Duke University botanist, hopes it will not be necessary to wait a half century or more to determine the effect of CO2 on the growth and diversity of plants. Strain has devised an experiment that duplicates the 21st century atmosphere in a section of Duke Forest. It will still be several years before any conclusions can be drawn from the experiment, but Strain believes that increased levels of CO2 already existing in the atmosphere have contributed to enhanced crop yields achieved during this century. No doubt, more than rice and soybeans will benefit from this ubiquitous gas.

It would be unreasonable to expect that all plants would exploit the added CO2 equally. There will inevitably be changes in the diversity of global plant life. William Schlesinger, who now manages the Duke experiment, believes that species diversity will suffer. "In almost every case in which a fertilizer has been applied to a natural community, it has reduced species diversity." He claims. The Earth may very well see more vegetation, but it would also see fewer kinds of plants, just as inevitably occurs when one dumps phosphorous in a lake or nitrogen in a grassland.

If the world is truly alive, we must re-think the carbon debate. In fact, we really ought to re-think environmental policy.

The best overall work on this subject so far is Tyler Volk's Gaia's Body: Toward a Physiology of the Earth (1998: Copernicus). Volk, an Associate Professor of Biology at New York University, takes the reader on a fascinating journey through Gaia's vital organs. The brilliant microbiologist Lynn Margulis has also written extensively on Gaia. As our understanding of this planet has improved, the Gaia theory has gained some formidable disciples.

If the Gaia theory holds true, there ought to be some mechanism to increase carbon burial in response to human activity. Pedro Verdugo has recently discovered at least one possibility.

Verdugo, a Professor of Bioengineering at the University of Washington, and his students, have identified a new carbon burial mechanism in the world's oceans. Verdugo noted that a large pool of organic carbon resides in the world's oceans in the form of dissolved organic matter ("DOM"), and has described a means by which DOM assembles into microgels and becomes particulate organic matter ("POM"). His studies indicate that these POM microgels can undergo crystalline mineralization, or phase transitions promoting their sedimentation to the ocean floor, eventually abandoning the food chain. Conversely, these microgels can increase the turn over of organic matter, by allowing bacteria to colonize and digest the assembled polymers in the gels' matrix, which would otherwise be difficult for the bacteria to capture and degrade. Whether the carbon is buried, or recycled, depends upon a number of factors.

Verdugo has found that crystalline mineralization of marine microgels is due to the predominantly negative charge of the polymers that form the DOM pool. As the inside of these small microgels form a negatively charged environment, they attract and concentrate (by what is called a "Donnan mechanism") Ca and Mg ions that are abundant in sea water and that carry two positive charges. Their studies show that due to the high Ca concentration in the matrix gels, slight changes in acidity --that don't affect the solubility of Ca in sea water -- can produce precipitation and crystalline mineralization of Ca carbonate in these microgels. The formation of these insoluble crystals increases the density of these marine microgels and results in sedimentation falling to the bottom of the ocean, excluding their organic matrix from the food chain and eventually creating a carbon sink. In this fashion, carbon joins the chalky sediments at the bottom of the sea. The probability that free polymers from the DOM pool -- which are linear molecules -- can assemble forming microgels is a function of the second power of their length. (Unfortunately, ultraviolet light, which can penetrate up to ten meters into sea water, can readily break up polymer chains, interfering with their ability to assemble. The thinning of the world's ozone layer from the release of CFC's may therefore slow the rate of gel formation and crystalline mineralization, slowing the rate of carbon burial.)

The rate of carbon burial is also affected by pH and temperature. If the oceans are slightly more alkaline than pH 8.5, or if the oceans cool a bit, there is a higher rate of crystallization. Higher crystallization means higher carbon burial and less recycling. Verdugo's findings were published in the February 5, 1998 issue of Nature.

I met with Professor Verdugo in February, 1998, to discuss his studies. I was naturally interested in a positive feedback mechanism, some indication that the rate of carbon burial was rising in response to the increasing level of CO2 in the atmosphere. Verdugo claimed that he needed to research the matter further, but agreed that higher levels of CO2, which dissolves easily in sea water forming carbonic acid and calcium carbonate, could eventually lead to more mineralization.

Is the Earth in Trouble? No. As Lynn Margulis has said, "Gaia is one tough bitch."

Life has survived massive bolide impacts from outer space, huge variations in solar output, gripping ice ages, the shifting of the Earth's magnetic field and a host of other disasters that would make human perturbations seem puny by comparison. Life has already maintained a tenacious hold on this planet for some 3.8 billion years, and will exist here for another 5.5 billion years or so, until the world's oceans boil from the heat emitted from an exhausted red sun. Gaia evolved ways of coping with all sorts of disasters long before there were humans. She will survive us, too.

Is the Human Race in Trouble? Maybe. It seems that the Earth can heal, but we do not know how quickly. Gaia may not be able to react in time to save us from our own folly.

From the perspective of an organism with a life span measured in terms of eons, rather than decades, we humans may seem expendable. Indeed we are. More than 99% of all species to inhabit this Earth are now extinct, and Gaia takes it all in stride. As Margulis has said, Gaia is no doting mother.

Something we might do, whether it be eradicating our fellow species, releasing CO2, methane, chlorofluorocarbons, and other gasses into the air, or simply logging the world's rain forests, may well set in motion a cascade of events which will have very unpleasant consequences for us as a species. Our flatulence may well raise global temperatures, melt the polar ice caps and inundate coastal cities. The Gaia theory is no panacea for polluters.

In this regard, it would be wise for us to cut CO2 and other greenhouse gas emissions to more reasonable levels. The technology exists now to do so without seriously compromising our standard of living.

The Earth is a dynamic living organism, one which we do not fully understand. Though her wounds may heal, there is no need for us to inflict them gratuitously.