by Garrett Smith
On planet Earth, the main ingredients for life are carbon, oxygen, phosphorus, sulfur, and nitrogen. The rate of growth and abundance of life can be limited only by the availability of the organism to these resources. If unlimited resources are by to be accessed by a single E. coli cell, the cell will create a colony the size and mass of the planet Earth in about 3 and a half days. This would of course break the laws of physics just because of distribution of resources, but theoretically the exercise underscores the rapid growth of life. Most people at this point tend to bring up an obvious point. The Earth’s atmosphere is made up of approximately 75% nitrogen, and 20% oxygen, how could these elements be limiting growth? Further questions are raised once a good look is taken at the human field of chemical engineering. This field has been the most powerful attempt by humans to influence the world around them in a way to make it suit them better. What this means is, people have begun using chemicals to further the progress of human cultivation of lands, and to support the growing population. When the phenomena is related to agriculture, it is referred to as the Green Revolution. This field is the industrial application of chemistry. These engineers take advantage of non-spontaneous reactions to use energy to break compounds apart, or push elements together to create certain target, desired molecules from building blocks of what are usually considered waste products. Great strides have been made in the process of liberating certain elements from ubiquitous compounds such as oxygen from water, and nitrogen from the atmosphere. These changes have been massively implemented, and may affect life around the globe, including humans.
The Introduction of Oxygen into Earth’s Atmosphere
To explain the first point, oxygen was a fairly rare element to be found in the atmosphere of Earth, only in the oceans, in the form of H2O. Only the advent of photosynthetic cyanobacteria moving molecules through metabolic pathways released the Oxygen from the oceans, and forever changed the atmosphere of Earth. In the process, perhaps the first major extinction event occurred. Oxygen is a corrosive, highly toxic gas to almost all life on the planet. There was almost no aerobic (oxygenic) respiration prevalent among life at the time. This caused catastrophic losses amongst the diversity of life, as entire species unable to adapt were wiped out by the poison. Climatic changes of the Earth’s ecosystem never occur without heavy loss of biodiversity in inability to adapt. “The establishment of an oxygen-rich atmosphere dramatically altered the evolution of life on Earth” (Krump et al), as only a mass extinction can. The changes that oxygen caused were likely established over a geological timescale, likely hundreds of millions of years to exchange the gas in such a big reserve such as the atmosphere of a planet.
A Basic Understanding of Nitrogen
Nitrogen on the other hand, has always been the most abundant gas in the atmosphere since life was established on the planet. This begs the question of how in any way nitrogen can be a rare resource for any type of life to be found on the planet. This is explained by an odd little quirk of chemistry that is explained by valence electrons. Valence electrons are the outermost electrons in the “shell” of an atom. The shell is thermodynamically inclined to have a full shell of 8 electrons. The nitrogen gas atoms in the atmosphere form a diatomic bond with each other becoming N2. In this state, the atoms cannot be taken up by organisms and incorporated into organic molecules. The limiting rate of conversion of atmospheric to the organic, or usable form of ammonia, is the enzyme nitrogenase. The catch is that this enzyme is not ubiquitous, it is only present in very few bacteria that live mostly associated with the roots of certain, legumous plants. While “Nitrogen is generally considered one of the major limiting nutrients in plant growth,” (Emerich et al) it is furthermore a bottleneck of organic nitrogen production that is the ONLY sustainable source of organic nitrogen in nature. Every single atom of nitrogen in the human body, of which there are billions, first passed through this fixation process in the roots of plants.
Understanding the Haber Process
This statement has grown entirely less true in the past thirty or forty years however. The collective ecosystem of the planet Earth is facing a far more awesome production of chemicals than ever before. Chemical engineering, and specifically the Haber process can produce a truly staggering amount of product. The Haber process accomplishes fixation “by using high temperature (around 500 oC), high pressure (approximately 150-200 atm), and also an iron catalyst. Haber could force relatively unreactive gaseous nitrogen and hydrogen to combine into ammonia,” (Modak). Since these precursors are incredibly cheap and abundant, the Haber process allowed for awe-inspiring profits by producing nitrogen cheaply to be used in explosives and fertilizers. Haber was a German scientist around the outbreak of World War 2, and his method gained prominence due to the proliferation of explosives around the time. Recently however, humans have turned to a nobler goal of trying to cram more people into urban settlements around the globe. The Haber process is once more being perfected and used more wildly than ever before to produce fertilizers to artificially increase the yields of farmer’s plots. At a cursory glance, this seems like a wonderful idea, less starvation around the globe, more money to poor rural people on the outskirts of the inexorable human scientific and economic progress. Things may not turn out quite so simply. The scale at which the Haber process is being used has some frightening statistics attached to it. As has already been stated, “biological N fixation is the primary source of reactive N,” and it is “providing about 90–130 Tg N year−1 (Tg = 1012 g) on the continents.” The scary portion of this is that “Human activities have resulted in the fixation of an additional ∼150 Tg N year−1” (Galloway). This means that humans produce about 1.3-1.4 times more nitrogen than the bacteria around the globe, putting the global organic N output up by a factor of 2.35. This has caused a massive removal of one of the key bottle-necks to growth of life around the planet.
Consequences of Removing Bottle-necks for Growth of Populations
Bottle-necks are a representation of a mathematical function of the amount of living organism in a system. Statistics are a key resource in the study of populations and ecosystems, commonly known as Ecology. Of the many interesting subjects, carrying capacity is the most relevant at this time. “Ecologists define carrying capacity as the maximal population size of a given species that an area can support without reducing the ability to support the same species in the future” (Ehrlich et all). What Erhlich did not mention in his description of the topic is the overshoot.
Fig 1. Carrying Capacity Curve
The overshoot is clearly labeled in the graph above. It is the tendency for organisms to not have self control in the face of excess resources. This is of course, a personification of a population. For instance, a hypothetical population of deer exists in the woods next to George Mason pond. They live, and have a stable population size as their numbers get reduced by disease, old age, the impact with cars driven by crazy University students, and the amount of grass to be found in the field near the pond. These deaths get equaled out by the birth rate in the mating population. Now, a hypothetical crew of construction workers arrives and clears out part of the woods. Since there are no predators besides possibly automobiles, the deer do not mind the loss of cover too much. However, the field has been expanded. More deer are born, and more arrive from outside populations to feast on the grass. Eventually, the population of deer becomes huge, and the growth rate of grass cannot keep up with the consumption of the deer. The deer run out of food. Now many of the deer begin to die of starvation, and the population crashes down below the previous size. Eventually, there are few enough deer left alive, and the grass grows back. Whether or not the deer survives depends entirely on how fast their precious commodity grows. Now humans, in their infinite wisdom, have created massive population spikes in plants, but more importantly have created portions of land with extremely high resource concentration. More plants grow, but during the first rain these fertilizing compounds get washed away into other communities. The most exaggerated effects are when the elements, mainly organic nitrogen and phosphorus, make it to water. The plant-like algae and din flagellates that feed on them experience enormous blooms in population size. Population blooms so large, that during the night, when photosynthetic production of oxygen is gone, all the dissolved oxygen in the water is used up, and the entire pond or lake, or inlet of the ocean dies. The carrying capacity of oxygen use was hit, and the population was entirely wiped out within a few generation times.
Oxygen as an Example of Bottle-neck Removal
One of the biggest examples of runaway chemical production in the history of the globe was the production of Oxygen. This catastrophic event increased the percent composition of the atmosphere’s concentration of the toxic, oxidative gas, oxygen. This caused what is commonly believed to be the first mass extinction of life, where anywhere around of 70% of all species on the earth perished due to not being able to use oxygen to drive the process of cellular respiration. The rest of life adapted, and created an extremely efficient conversion of glucose, into ATP, which is the basic unit of energy in the cell. This change was on the scale of geological time, and while the concentrations of oxygen have changed more than the abundance of organic nitrogen, there is a sever discrepancy. Acknowledging that atmospheric oxygen had more easy access to most organisms, the fact remains that in fifty years, the abundance of organic nitrogen has more than doubled around the globe. Fifty years is less than the blink of an eye to the processes of global change that have operated on the earth for millennia. Humans have driven a change at so great a rate, that it has never been paralleled in history. The Green Revolution has been a constant throughout the progression of human civilization. However far humans push their crops, and their pastures is how high the global population of humanity will reach. There have never been any entirely successful attempts to slow population growth in human history. This overpopulation of cities has led to many crises, such as poverty, to wildfire spread of diseases such as the black plague and malaria by giving them enormous amounts of the transference vectors that are human bodies. Neighbors infect neighbors infect neighbors. Problems such as these have halted growth, but humans continue to fill the gaps caused by the lifestyle.
Conclusion: Consequences of Human Influence on Food Growth
The reckless disregard of human influence on growth of food has more consequences than just urbanization. Studies show that “excessive air- and water-borne nitrogen are linked to respiratory ailments, cardiac disease, and several cancers” (Wolfe et al). These direct consequences are beginning to crop up in human health. The Haber process has only just begun to change the ecology of the domesticated world, and its artificially accelerated rate of production will only decrease the gain that is to be had from this process of fertilization. Of course, the more dramatic and direct effect on human health would have to be the production of explosives that were previously too expensive to be made efficient for military use. Loss of life has ensued, but it is likely the ingenuity of humans when it comes to violence would have found another way to pull off the devastation. It is important to realize that the power of chemical engineering is extremely under-appreciated, and that there is no way to determine the true ramifications of humankind’s actions during these past few decades.
The scariest thing about the human race is the constant need for progress. Individuals trademark technological advances, and use them to establish dominance amongst their peers, and crawl their way to the top of society. Often, there is not enough pause given to whether or not humans should do something, rather than if they can. When it comes down to the green revolution, or the tendency for humans to invent some way of improving food resources, there are other scary factors. The Green Revolution is a manifestation of humankind’s push against the carrying capacity of the Earth, or rather the areas of the Earth they tend to congregate into. The biological imperative of keeping themselves alive, and the social behavior that allows empathy gives rise to a group mentality of expand, expand, expand, instead of consolidate, consolidate, consolidate. The warning signs of the oxygen crises, and the tell-tale marks of coming catastrophe loom, but perhaps there can be ways of averting it. The trend in technology has become an exponential curve, where newer, more powerful technologies build off old ones, and gaps in human knowledge and capability are constantly being filled in. Perhaps the by-products of this asymptotic ascendancy will come back to haunt the era of information, and perhaps new ways will be thought up of to deal with it. Either one of these alternatives will occur, but nothing will slow the biological imperative of the growth of the human race.
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