The earth

by prof. Carlo Pellacani

During the 70s of the last century, James Lovelock postulated the Gaia Hypothesis through which he proposed the existence of a global balance involving the Earth physical conditions and the planet life. However, years later the physicist E. Lorenz from the MIT proved that the oceanic and atmospheric flows, as well as life itself, are not steady phenomena. All the more, Lovelock did not consider many astronomical events that were almost unknown at the time, such as meteorite falls, comets and the consequences of the Earth movement through space, since it follows the Sun while is orbiting the centre of the Milk Way, the spiral galaxy composed of 200 billion stars, ours included. The balance theorised by Lovelock is impossible to conceive nowadays. Let’s thinks about the Earth history for a moment.
Our Solar System was born about 4.6 billion years ago from a giant cloud of gas which collapsed due to gravity attraction, creating the Sun and, then, the planets of the system.
We do not know how many planets populated our system back then: at first, they probably had unsteady and nonlinear trajectories. For example, the astronomers are almost convinced that the Moon’s origins are to be searched in a violent collision that involved the Earth and one of this small primordial planets, which did not survive the impact: the debris of this cosmic collision scattered around the Earth and subsequently gathered into one block and formed our familiar satellite.
According to the most recent studies, the presence of such a great amount of water on our planet could be explained through a bombardment of meteorites and comets containing water which has lasted hundreds of thousands of years. We already knew that comets have a solid mass mainly composed of ice, however we recently discovered that the meteorites contain salt particles in which water can be found.
At first, the Earth atmosphere composition was different: less dense, so that the small or big meteorites could easily go through it. At that time, the Sun and the Solar System formation might have scattered a large amount of material, that later fell back on earth. The atmosphere was composed only of steam, carbon dioxide, nitrogen and other gases in small quantities; the oxygen was not present, however it is a fundamental element that allows all kinds of animals of our planet to breathe. The solar radiation was so intense that life was not possible on the earth surface.
For this reason, the first traces of life appeared in the deepest oceanic waters about 2.5 billion years ago, in the form of anaerobic microbes which did not need the oxygen and were protected from the cosmic rays by a thick layer of water (the figures could change in accordance to the most recent discoveries).
Later on, we see the arrival of seaweeds able to photosynthesise and produce oxygen, that at first dissolved in the oceans and then in the atmosphere. The lighter hydrogen reached the cosmos, abandoning the terrestrial atmosphere, that gradually stabilised in the current composition: 21% of oxygen, 78% of chemically neutral nitrogen, and 0.03% of carbon dioxide. This composition is constantly changing, probably as a consequence of the human activities, and, together with other substances, it is generating the greenhouse effect and the raising of the global temperature. However, it should be mentioned that the earth atmosphere has gone through warm and cold periods in the past, even if the current effects of industrialization could not have influenced it.
This high percentage of oxygen is the responsible of Life as we know it. From this point of view, the Gaia Hypothesis somehow confirms that life developed not only as a chemical and physical consequence, but also for innate reasons. If this (microscopic) seaweed had not appeared in the depths of the ocean 2.5 billion years ago, the atmosphere would not have had a composition favourable to the insurgence of life on the planet surface.
The current level of oxygen is balanced by the works of plants and trees that, as the seaweeds did in the dark waters, produce it during the night. Therefore, thanks to the green life, which preserved the oxygen level, the animals were able to migrate from the water and reach the dry land. For this reason, many environmentalists fight against the destruction of big forests, such as the Amazonian one. Anyways, the continents originated from several geological processes. Life as we know it (meaning oxygen breathing) was generated around 580 million years ago from the formation of the continents and the oxygen production of seaweeds and, later on, plants and trees that led to a change in the breathing apparatus of the existing creatures. Nonetheless, the vast oceans of our planet are a consequence of external factors.
During the Cambrian period (540 million years ago), according to geologic evidence, our planet witnessed a true explosion of life. The estimates indicate that of all the species that appeared during that time, only 1% survived. Based on current data, the number of extinct species reached several billions, while the living ones, according to scholars, can vary between 10 and 14 million (many species are still unknown and we constantly discover new ones). In some ways, these discoveries support Lovelock’s hypothesis, because they indicate that a “collaboration” between the earth and the life on earth has taken place in the past; all the more, it is clear that the evolution of the earth surface has played a big role because it created the dry lands, promoting a shift to oxygen breathing into the living creatures, that slowly started to live out of the water. In the depths of the oceans the anaerobic microbes are still present, especially close to volcanic emissions.
More than 65 million years ago, the dinosaurs were wiped off the face of the Earth due to the sudden decreasing of the temperature which was caused by the fall of a giant meteorite (its dimension reached 10 kilometres). The impact with the earth surface generated a dust cloud that obscured the sky for many years and cooled down the global temperature. Since the dinosaurs were cold-blooded reptiles and needed the sun rays in order to store their energy, they all died, however we cannot exclude the possibility of another unknown event that generated this climate change. By now, the meteorite hypothesis is commonly accepted. From that moment on, the mammals’ evolution has been easier, since they were able to keep the foetus to an ideal temperature in the womb; during the dinosaur era, the few existing mammals were small, similar to huge rats and lived in underground burrows to keep warm. Those small survivors are the ancestors of all the mammals that populate our planet nowadays, humans included. If the meteorite hypothesis is correct, once again we are witnessing the crucial role played by a cosmic event in the evolution of the planet life.
The first primates arrived more or less 65 million years ago: they could grab things with their fingers and probably lived in the forests. We can identify two suborders regarding primates: the Prosimians and the Anthropoids. In the first one some species similar to lemurs are still included, mainly nocturnal animals.
The Anthropoids were day-time animals: their eyes could distinguish various colours and the brain was bigger than the Prosimians’. We believe that they made their first appearance in Africa and then evolved in several ape species. The hominids, according to scientific theories, descend from the Anthropoid order.
Their arrival raises a complex question: their physical structure suggests that they were forced to abandon the forest and move to a desert environment by another climate change. Actually, the number of fossils that can be identified as our ancestors is constantly growing as we make new discoveries. Several fossils date back to the period that goes from 10 to 5 million years ago.
Among all the fossils, those that confirm the presence of a primate that could walk upright have been identified. In 1994, we found evidence of an Ardipithecus which dates back to 4.4 million years ago.
Traces of a humanoid who lived 2 million years ago allowed us to classify him as Homo habilis; another fossil was found in the north of Kenya. The Homo erectus has been found in Africa and the Homo Neanderthalensis found in Europe seems to come from 100,000 years ago. The traces of the Cro-magnon, that can be identified with the Homo Sapiens species, have been discovered in Europe and Africa, his first appearance dates back to 40,000 years ago. According to the experts, the Homo Sapiens could communicate through a primitive language and his DNA structure confirms that the entire humanity comes from this species. Around 13,000 years ago, the Homo Sapiens became the dominant species on Earth, at least according to the official theory that could be modified in the future.
During the industrial era, the man has started to modify the atmosphere and other elements. The Gaia Hypothesis does not consider the climate changes coming from external factors that, how stated above, have determined the evolution of the living species. However, this hypothesis captures with amazing precision the issues of the present time.
One of the hardest challenges for a climatologist is to foresee if the changes brought in by the industrial era will have consequences on the relationship between the various elements that should maintain a balance and that no one can actually identify since our planet and its life form together an unbalanced system. The formulation of future forecasts is a mathematically complex calculation, especially since data confirm that the atmospheric flows are a chaotic system in which a butterfly flapping his wings in Hawaii can generate a storm in another area of the planet. It should be clear then that with this premise the Gaia Hypothesis loses its value: a chaotic system can generate sudden and unforeseeable changes. Our planet is constantly evolving: each year the mountains have a different height and a fertile area can turn into a desert, or the other way around. The Sahara Desert was a fertile area up to 11,700 years ago; its desertification is the subject of several theories, involving the Monson winds and the oceanic flows. Due to the chaotic nature of the atmosphere, a trustworthy forecast, meaning a forecast formulated with numeric models and not subjected to serious mistakes, is linked to a temporal limit that goes from 7 to 15 days.
Although the Gaia Hypothesis includes some evident interactions concerning life, the geology and the atmospheric and oceanic flows, it does not consider all the changes and the sudden events caused by the complex nature of the universe, such as the meteorite falls (here we speak of big meteorites, since the small ones are constantly falling on our planet and we do not notice them because the vast majority of the Earth’s surface is covered with water). Actually, a large number of effects produced by the cosmos that affect our planet are still unknown and the theory of the life evolution on Earth is only valid when we consider the world of bacteria which is rapidly evolving in an easily observable experimental environment, however its application is definitely more complex when we consider longer time scales and bigger animals.