For the first concept presented above, for conventional renewable energy sources, they are replenished by sunlight or radiation from Earth’s interior; one is fusion, and the other is fission. For so-called non-renewable energy sources, such as hydrocarbons and fissile materials, they are either renewed on timescales so vast that they are effectively non-renewable for humans (such as ), or are “renewed” by the (fissile materials), so could only be renewed with new planetary formation. In mainstream thought, the currently non-renewable energy resources are primarily hydrocarbons (petroleum, coal, and natural gas) and uranium. Much of the debate centers around the definition of oil. What has been called oil for the past 150 years is today called . It is the oil formed by the , and can be mined by drilling wells and extracting it with the conventional methods that have been used since the beginning, and new techniques are periodically invented to increase the rate and total extraction. For conventional oil, humanity has unearthed about 1.1 trillion barrels since 1859, and about as of 2014. Production of conventional oil peaked in 2006 at 25 billion barrels per year and has declined since then. At current production rates, conventional oil will be completely depleted in less than 50 years. About another five billion barrels per year are called unconventional oil, which is called heavy oil, extra heavy oil, and oil sands. Those unconventional oils comprise trillions more barrels, and total and arguably more. For fissile materials, primarily uranium, the peak may have already been reached by 2014, or it . For , in that the peak may have already been reached, or it is only a few decades into the future at most. For coal, may also be only a few decades into the future. Peak extraction usually occurs when about half of the recoverable energy resource has been mined. In summary, the energy resources that have powered the Industrial Revolution are all on their way to largely vanishing in this century. The only resources with seeming viability past this century are coal and unconventional oil, which brings us to the second concept: .
On land, the devastation was similar. Again, insects , and several orders of insects vanished from the fossil record after the Permian; those of Paleozoic times also vanished forever. Permian forests gave way to deciduous forests in the wake of global warming, and early gymnosperms and seed ferns were largely replaced as made a comeback in the early Triassic. The lycophyte radiation in the wake of the Permian extinction is typical of what are called , which are the first organisms to colonize disturbed environments. Reptiles and amphibians lost nearly two-thirds of their families, which translates to more than 90% of all species. All large herbivores and predators went extinct, along with gliding reptiles. In total, the Permian extinctions wiped out about 90-96% of all species, more than 80% of all genera, and nearly 60% of all families. Nothing else in the history of complex life comes close and puts the Permian extinction in a category all its own.
Out of the Silent Planet by C.S
During that “,” , , and the rise of grazing and predation had eonic significance. While many critical events in life’s history were unique, one that is not is multicellularity, , and some prokaryotes have multicellular structures, some even with specialized organisms forming colonies. There are , but the primary advantage was size, which would become important in the coming eon of complex life. The rise of complex life might have happened faster than the billion years or so after the basic foundation was set (the complex cell, oxygenic photosynthesis), but geophysical and geochemical processes had their impacts. Perhaps most importantly, the oceans probably did not get oxygenated until just before complex life appeared, as they were sulfidic from 1.8 bya to 700 mya. Atmospheric oxygen is currently thought to have remained at only a few percent at most until about 850 mya, although there are recent arguments that it remained low until only about 420 mya, when large animals began to appear and animals began to colonize land. Just as the atmospheric oxygen content began to rise, then came the biggest ice age in Earth’s history, which probably played a major role in the rise of complex life.