Earth is the Planet of Life. A myriad of plants, animals and human being thrive on its surface and under the sea. We are so accustomed to it, to forget frequently that life is a rarity in our solar system. Even on Earth the Biosphere is limited to a very thin layer, with few exceptions, less than ten kilometers across, from the high mountains to the deep seas.
Scientists explain this state of affairs with a character from the fairy tales. They call it the Goldilocks Principle. Remember the fair-haired girl who went to the bear’s house? “Not too hot and not too cold, not too big and not too small, not too hard and not too soft, but just right!”
We do not know exactly how and when life started on Earth, but we understand very well why life is on it now. Our planet is at the right distance from the Sun, its atmosphere has the right composition and pressure of gases; day, night and the Seasons come and go with the regularity of a clock. Last, but not least: our Big Blue Marble is the world of water, liquid water. This is very important: where there is no water, there is no life.
Spacecraft sent to Venus and Mars, our neighbor planets, were not able to discover life on them. The former is about the same size of Earth, but has a very hot and dense atmosphere, so dense in fact that we cannot see its surface. Mars is about half the diameter of Earth and has a very thin atmosphere. Both atmospheres are composed mainly by carbon dioxide (CO2). This gas plays an essential role for life; it contributes by keeping the right temperature on the planet surface. The Sun emits most of its energy as electromagnetic radiation in the range of infrared, visible and ultraviolet light. Ultraviolet radiation is almost stopped in the upper atmosphere by a thin layer of Ozone; visible light is used by Photosynthesis. The CO2 traps the infrared radiation near the surface in the right amount to keep it warm enough to sustain the existence of liquid water and life.
The process is known as the Greenhouse Effect. Volcanic eruptions are the main natural source of carbon dioxide on Earth. Apparently when life started on our planet, the photosynthetic process followed relatively soon, trapping CO2 and creating molecular Oxygen, used by animal and human life.
This is a simplified description, written just to remind some factors determining our existence on Earth and the link between them. The process involving life is, of course much more complex and cannot be described in a few lines, neither this is my intention. My intention is to emphasize that very little changes in the existing conditions might easily transform Earth in a lifeless planet like our neighbors Mars and Venus. How much narrow is the Goldilocks zone in space and time? Lets start from time:
As far as we know life started on Earth about three and a half billion years ago when there was almost no oxygen in the atmosphere. We do not know much about the temperature on the Earth’s surface then, but it ought to be not much different from the present temperature, otherwise the chemical processes involving life could not be sustained. Then Photosynthesis arose. Blue-green algae used the abundant carbon dioxide and freed molecular oxygen in the air, making possible the existence of animal forms of life and ultimately intelligent forms of animals, the human beings, who could ask themselves how all this came to be. We understand that in order to sustain living things for a time long enough to create thinking human beings, the atmospheric temperature, pressure and gas composition ought to be steady for at least a billion years, otherwise we could not be here to tell the story … or could we? Perhaps life, as we understand it, is possible also under different conditions. Life perhaps is, but as far as we know, a complex form of life as we are, is not. Unclothed men cannot survive for long if the surrounding temperature is less then a few degrees above zero Celsius degrees, neither they can live in the desert, where the mean daylight-hours temperature is more than the body temperature. With the exception of a few specifically adapted deep-sea animals, complex life needs ‘atmospheric’ pressure and an oxygen concentration not too far from the present one.
Believers have a straightforward explanation: all this is the Hand of God. Scientists make a difference between Physics (Science in general) and Metaphysics (Religious believe). They call it ‘The Anthropic Principle’ which states that ‘were the conditions different, the man (Greek= anthropos) could not be here and tell the story. In this case, to my modest opinion, the difference between science and religion is just semantic. The argument is only about whether a Superior Will is behind our existence. Religion gives it for granted; Science cannot give the answer and does not really care to give one.
We have been here, whatever the reason, for a long time, surrounded by a very stable global environment and we might come to the conclusion that some mechanism is acting to preserve the steady state. Perhaps whenever some natural process causes a shift from the equilibrium, there is some other natural process that opposes it, bringing the situation back to the original point. We can think of at less one such negative feedback mechanism, which apparently kept the atmospheric CO2 concentration very stable over the eons: during periods of intense volcanic activity, when more CO2 was released in the atmosphere, vegetal life was favored by the high gas concentration. The plants thrived. When the volcanic activity subsided, the more extended forests used more CO2 and lowered its concentration even below the normal level. But the explanation above is just a mere simplification. Other factors might have contributed: perhaps plants thrived also because of the higher temperature caused by the CO2 greenhouse effect or because of a rainy period caused by the particles seeded in clouds by the volcanic activity.
When scientists try to explain the past Earth’s history, they face a serious problem. They can make perhaps good logic speculations, but they lack directly measured data. Sometimes even the most powerful methods contain an intrinsic bias. One method to keep track of the past global temperature is based on measuring the growth rings of fossil trees. But this is exactly why it cannot be used to assess the part played by the temperature influence on plant growth. It’s the classic chicken-and-egg problem!
I am not saying, of course, that all the scientific methods are flawed. The opposite is true. Modern science gives us solid estimates about the past environment conditions on Earth, but because so many factors were involved it is very hard to assess whether we can speak of long-standing steady state conditions or not.
Physics tell us of two types of equilibrium: stable and unstable. We define that a physical body is in stable equilibrium when, if moved, tends to return to its previous position; on the other hand, a body is said to be in unstable equilibrium when, if slightly moved, tends to run away from its previous place. The same rule works also for large physical systems like the global life-sustaining environment: Are we like a billiard ball in the pocket or like a boulder poised on top of a hill?
I will rather describe the situation in a slightly more complex way. Our environment is like a boulder on the top of a particular hill: the top is, in fact, a broad plateau, scattered with potholes and bumps. Our boulder is moving on it, driven by the forces of Nature. Since these forces push the boulder at random, it wanders around the plateau’s center, spending most of its time in stable depressions, less time roaming from a high place to another. Since the man appeared on the scene, though, he pushed the boulder steadily in one direction. At first the human-driven force was negligible, against the huge random pushes of Nature, but from the Industrial Revolution on he pushed harder and harder. As a result the boulder’s random movement approached more and more the edge of the plateau.
Before we take a deeper look at some of the natural and human-driven forces that cause the shifting-from-the-equilibrium effect on the Earth’s environment, lets understand better how the cause-effect game works.
Does 1 + 1 always give 2? Not quite. Did you hear of the synergic effect?
Synergy is a Greek word. It means: “Work together”. It can be seen when you bring together some factors that singularly can cause a small effect, but if they are put together, they cause an effect much greater than the sum of the single effects. Lets give an example: A fat man is driving his car on a mountain road; his fat mother-in-law is sitting in the back seat, on the driver’s side. They put a heavy suitcase on the roof of the car. The car’s weight is slightly unbalanced, though not so much, since the car weights a ton and the difference between its left and right side is a mere few tenths kilograms. The man is driving down the road at moderate speed. There is a small oil spot on the asphalt. When the car reaches the spot, it skids and is driven almost off the road, but the man and his mother-in-law are lucky: the man manages to stay on the road, thanks to the low speed, the slight unbalance and the small spot.
Each one of the three factors, though small enough itself, combines in a greater and, in this case, dangerous effect.
But this is not enough. Let assume for a moment that our man is fatter, so his mother-in-law is. They have, of course, a heavier suitcase. The man drives his car a little faster and, alas! The oil spot spread on the asphalt and is now a little larger. Small differences.
What will happen now? Will the man be able to stay on the road, or the car will fall off the cliff? Remember the synergic effect? Small differences build up in much greater results. The car will skid uncontrollably and most likely will fall off the road.
Let now consider another factor: time. The man drives his car on the same road not once, but every day. What the chances are that he will manage to stay on the road every time he drives on the oil spot? We have to consider that what we are describing does not happen exactly the same way all the times. The oil spot may be in different places, the speed is not the same all the times and the man can be distracted now and then by the mother-in-law yelling on him. Time has a cumulative effect. Give enough time and things with a small probability to happen will happen at last. Perhaps this is a more serious way to describe the ignominious Murphy’s Law. A last thing we have to consider is the threshold effect, the point of no return. Whatever small the probability is to go off the road, once it happens statistics are worth nothing. The poor fat man and his mother-in-law are down the cliff. There will be no tomorrow for them to refine the theory.
But our fat man is no so stupid. He quickly realizes that something is wrong and takes the needed measures.
He understands that some factors, like the oil spot, are not under his control. He may be not aware of other facts, like the car unbalance, but surely he can reduce the car speed in the dangerous tract and … tell his mother-in-law to keep her big mouth shot!
Generalizing, we can say that small factors might cause a major effect. Small increments of the factors cause an exponential growth of the resulting effect. Time has a cumulative influence and, if the effect reaches a certain threshold, there might be a point of no return. And if you don’t do anything to avoid that, do not blame the Murphy’s Law, which states, as well known, that “If something can go wrong, it will”.
When we think about natural threats that can wipe out our existence from the world, we are used to imagine big catastrophic events: comets hitting Earth, worldwide spread epidemics, sudden extreme global changes of climate and so on. We know that such catastrophes happened in the past and it is good advice not to underestimate them, but they are extremely rare. We care much less of gradual changes that may endanger our existence in the long run. Our attitude regarding environment degradation is similar to our attitude regarding crawling inflation. When money is losing slowly its value we snort about the rising price of gasoline and… we get quickly used to the new price. Once in a while the niggling statisticians remind us that we are refilling our tank at the same price that just ten years before could refill it twice.
Allow me to tell you about a personal experience. I am a middle-sized man. Not too fat, nor too thin. Last winter I put on some overweight. Not much, about a couple of kilos. Nobody noticed it, nobody said a word, but when spring came I found that none of my last-fall trousers fitted on me. All the overweight had concentrated on my belly! I went to the next men-fashion store and bought three new pairs of trousers. Meanwhile I did not throw away the other trousers, all in excellent conditions. I left them in my closet, hoping to wear them as soon as I lose the overweight by diet and physical exercise. I know it will never happen. I will dispose of them next spring, when even the new ones will hardly fit on me and, of course I will pay another visit to the men-fashion store! I am sure that more than one reader had a similar experience.
Natural changes are very slow compared with the human life length. Oceans are created and disappear, mountains are washed to the sea, but we cannot notice it. Meanwhile also plant and animals change. They adapt themselves to the changing situation. In fact they do not. Some of them perish, other survive and generate seeds and offspring better adapted to the changed environment. This is the game of Evolution and Natural Selection, so well described by C. Darwin one and a half century ago. The survival of living things is possible only because Nature gives enough time, only because the environmental mutations have a scale of time in the order of million years. We know that when some environment changed drastically during a thousand years or less, most of the living species involved was not able to adapt themselves and became extinct. There is no reason to think that this natural process will change in the future just because… we wish it to be so.
We build dams, divert rivers, dry seas, dig quarries, and in a word change the environment at a much more swift pace than Nature. We are changing the game’s rules. Most of those changes cause also unknown effects. Most of the human activities, though, have nothing to do with global environmental changes. They are important only on a local context. But other activities are affecting the global environment. The burning of rain tropical forests, for example, to name just one. We must not be ashamed for everything bad that happens on Earth. Most of the catastrophes, in fact, were, are and will be caused by Mother Nature herself, but man always has the bad habit to put himself over Nature; never really taking the responsibility involved by the role he plays.
Too often we ignore that our activities might trigger some dormant natural forces that we will not be capable to control. In fact we might be completely unaware that we were the prime cause of some natural catastrophe. When cause and effect are separated by time and space it is very hard to see the link between them. Like the butterfly flutter in Peking that causes (according to the Chaos’ Theory) a thunderstorm in the US East Coast.
Some of us are concerned about endangered species that might be wiped out by human activities. Whales, Pandas, Citas are certain in peril. What about Homo sapiens? We are another endangered species, and this is because we are substituting Nature with an artificial environment, having no idea whether we have the needed natural fitness to overcome the natural selection barrier involved in such a substitution. Is what we are doing to our environment an Evolutionary Suicide?