The first tree forests formed in the late Devonian, and bark is the great innovation that led to forming the Carboniferous’s vast coal deposits. Compared to modern trees, Carboniferous trees seemed to go overboard on bark, at least partly to discourage arthropods. Today’s trees generally contain at least four times as much wood as bark. Those early trees had about . trees dominated the Carboniferous rainforest and could grow 30 meters tall. Because it took more than a hundred million years for life to learn to break down lignin, that early lignin did not degrade via biological processes. The early Carboniferous was warm, even with a small ice cap at the South Pole, and Earth’s first rainforests appeared in the late Devonian and again proliferated in the Carboniferous. The Carboniferous lasted from about 360 mya to 300 mya and was the Golden Age of Amphibians, as the rainforest was largely global in extent and swamps abounded. Amphibians were the Carboniferous’s apex predators on land, and some reached crocodile size and acted like them.
In the oceans, the Carboniferous is called the Golden Age of Sharks, and ray-finned fish arose to a ubiquity that they have yet to fully relinquish. Ray-finned fish probably prevailed because of their high energy efficiency. Their skeletons and scales were lighter than those of armored and lobe-finned fish, and their increasingly sophisticated and lightweight fins, their efficient tailfin method of propulsion, changes in their skulls, jaws, and new ways to use their lightweight and versatile equipment accompanied and probably led to the rise and subsequent success of ray-finned fish in the Carboniferous and afterward. , which are amoebic protists, rose to prominence for the first time in the Carboniferous. Reefs began to recover, although they did not recover to pre-Devonian conditions; those vast Devonian reefs have not been seen again. did not appear until the . Trilobites steadily declined and nautiloids familiar today, and straight shells became rare. The first , which were ancestral to squids and octopi, first appeared in the early Carboniferous, but some Devonian specimens might qualify. Ammonoids flourished once again, after barely surviving the Devonian Extinction. This essay is only focusing on certain prominent clades, and there are many and . The early Carboniferous, for example, is called the Golden Age of , which are a kind of , which is a phylum that includes starfish. The crinoids had their golden age when the fish that fed on them disappeared in the end-Devonian extinction. Earth’s ecosystems are vastly richer entities than this essay, or essay, can depict.
Two primary events drove the first phase of the Ordovician-Silurian mass extinction: the ice age caused the sea level to drop drastically and the oceans became colder. When sea levels fell at least 50 meters, the cooling shallow seas receded from continental shelves and eliminated entire biomes. Many millions of years of “easy living” in warm, shallow seas were abruptly halted. Several groups were ravaged, beginning with the plankton that formed the food chain’s base. About 50% of brachiopod and trilobite genera went extinct in the first phase, and cool-water species filled the newly vacant niches. Bivalves were largely found in seashore communities, were scourged when the seas retreated, and lost more than half of their genera. Nautiloids were also hit hard, and about 70% of reef and coral genera went extinct. The retreating seas somehow triggered the extinctions, and whether it was due to simply being exposed to the air or changing and cooling currents, nutrient dispersal patterns, ocean chemistry, and other dynamics is still debated, and those extinction events are being subjected to intensive research in the early 21st century.
What I have yet to see human-agency skeptics discuss is that of multi-metric-ton herbivores and their attendant predators appeared hundreds of millions of years ago, and attaining large size was both an offensive and defensive strategy that goes back to the "arms wars" of the Cambrian Explosion. When mass extinction events happened, the race began anew. rose to prominence along with . When the wiped out those dinosaur guilds, it was not long before large herbivores began to reappear, with mammals in those niches. Within 25 million years of the bolide event, mammals reached their maximum size and , until humans arrived. Although species emerged and went extinct, just as they had for the entire eon of complex life, that guild stayed relatively constant in size. When humans arrived, . The five-to-seven ton herbivores and their predators vanished and were replaced by guilds a tiny fraction of their size. Car-sized inhabited a niche that once resided in, and soon after humans arrived, only dog-sized armadillos remained.
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In today’s hunter-gatherer societies, the EROI for killing large animals dwarfs all other food sources. The EROI, of calories produced divided by those burned during the hours of labor invested, for large game (a deer, for example), is more than 100, and on average four times that of small game, fifteen times that of birds, about eight times that of roots and tubers, and 10-15 times that of seeds and nuts. The hunter-gatherer EROI for seeds, nuts, and birds is around ten-to-one. An average-sized adult African elephant carcass provides about 13 million calories, which would sustain a band of 12 people for a year if they could eat it all before it rotted and did not die of protein poisoning. The EROI for those easily killed proboscideans when humans invaded the Western Hemisphere could have been in the hundreds and even more than one thousand. Large animals have always been the mother lode of hunter-gatherer peoples, and the consensus among anthropologists is that no instincts urge a hunter to kill only what is needed, but a hunter will kill whatever he can. That finding partly derives from studying modern hunter-gatherers. There is no doubt that when early humans intruded into environments that never before encountered humans, where animals would have had no intrinsic fear of humans, people would have had an exceptionally easy time killing all large animals encountered. Animals without experience around humans, such as Antarctic penguins, are easily approached and killed. As happened innumerable times in the historical era, intruding humans killed all the naïve animals that they could. The only animals that survived developed a healthy fear of humans and avoided them, but how many could develop that fear before they were all killed? From the very beginning of the , . More than 500 million years later, a new kind of animal appeared that turned that advantage into a fatal disadvantage, as it found a way to mine that energy stored in large animals, and it quickly plundered it to exhaustion whenever it could.
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The relatively gentle river valleys of Mesopotamia and Egypt saw long, slow declines in their environments, but when civilization came to the more mountainous periphery of the Mediterranean Sea, environmental damage came much faster and more dramatically, particularly as the Stone Age gave way to the Bronze and Iron ages. Before civilization arrived, the Mediterranean’s periphery was heavily forested and, as with Lebanon, cedars were plentiful. Today, Lebanon has several small groves of cedar, as a kind of museum of former greatness, and efforts to are ongoing. The about , and island-dwarfed hippos and elephants went extinct soon after humans arrived. Any land that can support hippos is blessed with an abundance of water, and islands such as Crete and Cyprus were blanketed with verdant forests before the rise of civilization.
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Many reasons were proffered to explain the Minoan decline and collapse, including the . What is increasingly cited as the reason for the Minoan decline (and was probably the ultimate reason for its collapse), was that Minoans , primarily via deforestation. Minoans, just as with many other collapsed civilizations, exceeded their land's carrying capacity. For organisms, carrying capacity always meant food and the ability to reproduce, but for civilizations, it also meant the energy needed to run the civilization’s moving parts, including transportation and the energy used to build structures and goods. If we revisit the “” that life faces, whether to use energy to fuel biological processes or build biological structures, civilizations faced the same choice. Humans commandeered the energy that a tree invested in its growth, and there were two basic ways to use it: liberate the energy in the structure by burning it, or use that structure for building human-usable tools or structures, which included buildings and ships. , as did pottery-making and fireplaces and furnaces to heat buildings. Minoans also built a tremendous fleet of ships for trade and military dominance. When rebuilding Minoan palaces, Crete’s inhabitants used wood exuberantly, but by 1500 BCE, the use of wood in palaces declined precipitously, and when Mycenaean Greece annexed Crete, the forests were gone and Greeks used Crete for pasturing their sheep.