What Happened In The Carboniferous Era_

The Carboniferous was a completely wild geological period, with immense forests, giant mosses, large horsetails, towering trees, and tree ferns surrounding dark and fetid swamps. Giant anthropods roamed among the low vegetation, while enormous flying insects buzzed at mid-height. And then amphibians. Amphibians everywhere. The first four-legged animals to colonize the planet, heirs of the first fish that had already managed to land on the shores at the end of the Devonian, had indeed become the dominant species and were increasingly differentiating into various shapes and sizes. Even the climate at the time was decidedly strange. Initially very hot, then cool, with carbon dioxide and oxygen up and down, in constant struggle with each other. And then the forests. They seemed like they could last forever and instead disappeared quickly, covered by hundreds of meters of deposits and fossilized into coal. All of this was the Carboniferous, perhaps the most gothic and dark geological period in history, with its swamps, ferns and relative absence of large land animals, making it look like a movie set waiting for actors to enter. A world suspended in time, where only the eternal drip of dew, sliding into the water from the outstretched fronds of ferns, managed to mark the passage of time. A world that was truly chilling, although, after all, much less dangerous than the worlds that were about to come. The Carboniferous belongs to the Paleozoic era. In fact, we can define it as the longest period of the Paleozoic, lasting 60 million years from about 359 million years ago at the end of the Devonian to 299 million years ago when the Permian began. The Devonian had left behind a mild climate and an atmosphere rich in carbon dioxide, brought about by intense volcanic activity. But in the Carboniferous, the CO2 content in the atmosphere decreased by at least five times in about 50 million years due to a combination of factors, such as the near absence of volcanic activity and the spread of forests that increased the uptake of carbon dioxide needed for photosynthesis. The biological consequences were significant. The collapse of the rainforest-like forests of spore-producing plants, ferns and horsetails, and the spread of cooler and drier environments allowed for the spread of seed-bearing plants without flowers like conifers and other gymnosperms, and the advancement of reptiles at the expense of amphibians. At the beginning of the Carboniferous, seeing a tree as we know it today was not something very common. In fact, it must have been rather strange and unusual. The rest of the vegetation had a rather simple and humble appearance, because the ground was predominantly covered by ferns and mosses, but there were not many plants towering over the horizon. At some point, some plants related to ferns, namely horsetails, developed a revolutionary stem structure that allowed these plants to grow to huge heights, from 8 to 20 meters. This adaptation proved to be successful because it allowed them to look down on other plants and ensure that they had sufficient amount of light. The only problem with this gigantism was the wind, which could often cause the stem to break under its own weight. Fortunately, the pith, a stronger flexible reinforcing structure that is still found at the center of the trunk of many trees today, appeared. At this point, trees began to spread rapidly across our planet, undoubtedly facilitated by the fact the continents were then united and the climate was homogeneous. Ferns diversified and were increasingly joined by plants that reproduced through seeds. The probably marsh and humid environment in some areas of our planet favored the spread of trees, with woody stems capable of reaching up to 30 meters in height. But things did not last. In the middle of the Carboniferous period, after millions of years of slow convergence, the continents completed the process of forming the supercontinent, Pangaea. This fusion of the continents also influenced the climate, interrupting the warm ocean currents that were previously able to penetrate between the landmasses. As a result, before the end of the Carboniferous period, summers became cooler and glaciers formed that eventually covered most of what is now South America, Africa, Australia, and Antarctica. The forests that covered much of the Earth's surface could not thrive in the changing climate. One of the main consequences of this was the Carboniferous rainforest collapse, which led not only to the extinction of the rainforests themselves, but also to the fossilization of dead trees and the formation of vast beds of coal. The reason why this fossilization process occurred almost exclusively in the Carboniferous period is due to some important developments in plant evolution, namely, the appearance of woody fiber and bark. These elements contain, respectively, lignin and subarin, substances capable of slowing down the decay of dead plants in such a way as to give them the time to fossilize into coal. This was further aided by the fact that decomposers such as bacteria and fungi had not yet developed the enzymes necessary to break down lignin and subarin. It is precisely thanks to these ideal conditions that most of the Earth's coal was formed in the Carboniferous period, and since then, comparable levels of coal formation have not occurred. Well, so far we have talked about climate, geology, and flora, but what about fauna, the animals? Fossil remains show that during the late Carboniferous, air-breathing insects, arachnids, and myriapods were present, and the seas were dominated by sharks that were increasingly diversifying their characteristics. But the most astonishing thing is that the entire period was affected by the phenomena of animal gigantism, especially concerning insects, arachnids, and amphibians. It is believed that these species grew more than usual due to the amount of oxygen present in the atmosphere at that time, which, due to the explosive chlorophyll photosynthesis of the forests, reached over 35% of their atmospheric composition, compared to today's 21%. Oxygen, a crucial element for life, can be toxic if taken in large quantities. In humans, an excess of oxygen causes damage at the cellular level, causing nausea, vision problems, breathing difficulties, and convulsions. Precisely for this reason, younger insects in the larval stage, as well as amphibian embryos, would have been forced to increase their size to avoid oxygen poisoning. If an organism becomes larger, its surface area for absorption will decrease compared to its volume, a sort of forced evolution whose purpose was undoubtedly to ensure the survival of the species. Despite this, amphibians were the most widespread vertebrates at that time. Some were similar to today's salamanders and newts, but others were as long as 6 meters, with very intimidating mouths and dentition. Toward the late Carboniferous, alongside amphibians that needed to reproduce in water and therefore could not stray far from the mainland, Hylonomus appeared, an ancestor of reptiles capable of reproducing by laying eggs on dry land. The evolution of the reproductive system thus marked the transition to a higher evolutionary level, allowing new species of amphibians and reptiles to move away from wetlands and colonize the mainland. They are the ancestors of the archosaurs, from which, about 100 million years later, the first dinosaurs were born. The giant insects of the time were many, but the most famous is undoubtedly the Meganeura, a kind of dragonfly that had a wingspan of almost 1 meter. Amazing dimensions considering that today's largest living insect is the Titanus giganteus, a beetle from the Amazon, which measures no more than 18 centimeters. The giant insects disappeared later when the amount of oxygen in the atmosphere significantly decreased, returning the insects to their original size. In an era in which, among other things, the first appearance of birds occurred, which would soon become the natural predators of insects. The latter developed a smaller and more agile body, capable of escaping more easily and performing faster, evasive maneuvers. Therefore, their air was colonized by insects, which were the first creatures ever to develop the ability to fly. However, on the ground, the arthropods of the time were just as impressive in terms of exaggerated size. It should not be forgotten, in fact, that among the shrubs it was possible to encounter scorpions up to a meter long, and also the famous Arthropleura, a species of millipede or centipede capable of exceeding 2.5 meters in length and 50 kg in weight, with a body composed of about 30 segmented parts protected with side plates. Fortunately, it was a solitary creature and perhaps rather timid. It could afford to be, given that it was at the top of its food chain and had few predators capable of worrying it. It had a thick, resistant shell over half a meter wide for its defense, and its strong jaws could deliver a nasty bite. However, it is unlikely that it could be poisonous. Apparently, it fed on vegetables. A study of the intestinal contents of an Arthropleura showed the presence of mosses, which were a significant component of the vegetation of coal swamps. There are at least five species of Arthropleura found throughout the world. All of them are extinct, of course, shortly after the collapse of the great rainforests. Ok, but now we want to leave you with a question. Could humans have lived during the Carboniferous period? Let's try to answer this. The biggest concern would have come from the amount of oxygen, which for our species could have dangerous long-term consequences. Another problem related to breathing could come from the abundant quantities of spores emitted by plants that were completely alien to us. Therefore, the possibility of extreme allergic reactions should be considered. We are more adapted to pollen, which did not exist in the Carboniferous. Water could be found everywhere, but a big problem would have been food. Without fruit, we would be forced to hunt some slow amphibians. The good news is that the animals did not have to be so dangerous during that particular period. However, it was possible to come across creatures as large as crocodiles among the bushes, so it would have been better to stay away from swamps and dense vegetation. We would probably have to build a shelter in the trees. This wouldn't be easy due to the absence of plants with branched trunks. Lighting fires to cook food or to keep insects away, which would certainly make our lives difficult, would be highly advisable. However, we would still have to pay close attention not to start fires that, with the percentage of oxygen present in the air, would quickly become uncontrollable. Finally, we must take into account the disorientation of our 24-hour circadian cycle, as, during the Carboniferous era, a day had a duration of only 22 hours of sunlight. In short, if we had a time machine at our disposal, we could make it happen, however, with a lot of caution.