Earth’s History in Five Elements: Sulfur, Nitrogen, Carbon, Hydrogen, and Oxygen
Interactions among those five elements have determined the state of Earth.
Earth is a ‘rocky’ planet. Most of its mass comes from elements that are solids. Then come the liquids, then the gases. (for all: at natural temperatures)
Sulfur and carbon exist as solids and gases in nature. Nitrogen, hydrogen, and oxygen are gases. The latter two can combine to form the most abundant liquid: water — which can also be solid or a gaseous vapor. (All gases can get trapped in solids, but that does not make the former constituent elements of the latter.)
Those five elements are especially important because they are the stuff of life. All life, from a single-celled amoeba to we humans, is formed of those elements. Life takes in those elements and returns them to the world, via exhalations, secretions, excretions, and in the end decomposition. [Note: sometimes phosphorous is included among the ‘basic elements of life’ and sometimes sulfur is disinvited.]
Oxygen is without question the single most important element. In all the Universe, only hydrogen and helium are more abundant. Most importantly, oxygen readily combines with any of the other Big Five elements (among many others — and while it can interact with phosphorous in a big way, it does not naturally combine with that element to form stable molecules).
There was a time when there was almost no free-floating oxygen on Earth. The atmosphere had lots of oxygen in it, but it was all combined with sulfur, nitrogen, carbon, and hydrogen. Only forms of life that could exist without the presence of free-floating oxygen, but could obtain that element via its presence in molecules that contained it as a constituent element, was present.
Water was one such molecule: all multicelluar life was in the water. On land, only anaerobic microbes, which did not require free-floating oxygen, could survive. Even plants could not exist on land in that atmosphere (which was too thick for sufficient sunlight to have penetrated to the surface).
Then came the Great Oxygenation Event. Cyanobacteria exploded onto the scene. They could live on land, taking-in carbon dioxide in the air and giving- off oxygen. They thrived, making free-floating oxygen such a significant part of the atmosphere (after several million years) that life on land got transformed. The anaerobic microbes, poisoned by all that oxygen, suffered a massive die-off (though some survive to this day in certain toxic, to all other life, microenvironments).
The table was set for plants and animals to take over the planet’s land with their symbiotic relationship: the former take-in carbon dioxide and give-off oxygen; the latter take-in that oxygen and return to the world carbon dioxide (and other elements nutritional to plants, especially nitrogen).
Still, Earth’s climate has not existed in a perfectly stable equilibrium. The planet has had warmer periods and colder ones. Mostly, those have been determined by the amount of carbon dioxide in the atmosphere.
Animals are not the only source of carbon dioxide. Events of a geological kind — volcanoes and magmas flows — release carbon dioxide (and other oxides) into the atmosphere. At times they have been frequent/large enough to change the composition of the atmosphere enough to warm the planet to the point that a tropical climate reached almost to the poles. Conversely, when the amount of carbon dioxide in the atmosphere has been significantly diminished the planet has cooled, with glaciers reaching all the was across the temperate zones. There has been one geologic instance when the entire planet was covered in ice — which ended as a result of increased geological activity.
Currently, carbon dioxide is again increasing in the atmosphere. This time it is coming mostly from the burning of fossil fuels by humans. As it continues to increase the climate of the planet is again changing.
Here’s the problem: civilization: the existence of cities. Cities depend on the existence of farmers and ranchers to supply them with food. The ability of farmers and ranchers to produce enough food to sustain the cities depends on the climate.
Cities arose soon after farming arose. The two have existed together, the one depending on the other for its existence, for several thousand years.
Even the Bible bears that out. Estimates of the age of Earth derived from it correspond with age of farming/cities. According to the Bible, a son of Adam and Eve, Cain, who was a farmer (and murdered his brother, Abel), “built the world’s first city.”
During all that time Earth has had the same climate. It has been slightly warmer or cooler here or there, but during that time the planet has experienced nothing close to the changes that we are now producing.
If the change in climate were to be a smooth, continuous process we could probably adjust and be O.K. That is not the case. The transition from the climate Earth has had for the last several thousand years is starting with disruption. We are experiencing chaotic swings from one extreme to another. There is no chance that the global system of producing and transporting the food necessary to feed the cities will survive for very much longer.
Most of the seven or so billion people on the planet live in cities. If civilization collapses those teeming hordes will flee the cities, overrunning the countryside — all due to an increase in carbon dioxide. As ever, to paraphrase a great old song, ‘the elemental rules apply’.