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But the branch of the that readers might find most interesting led to humans. Humans are in the phylum, and the last common ancestor that founded the Chordata phylum is still a mystery and understandably a source of controversy. Was our ancestor a ? A ? Peter Ward made the case, as have others for a long time, that it was the sea squirt, also called a tunicate, which in its larval stage resembles a fish. The nerve cord in most bilaterally symmetric animals runs below the belly, not above it, and a sea squirt that never grew up may have been our direct ancestor. Adult tunicates are also highly adapted to extracting oxygen from water, even too much so, with only about 10% of today’s available oxygen extracted in tunicate respiration. It may mean that tunicates adapted to low oxygen conditions early on. Ward’s respiration hypothesis, which makes the case that adapting to low oxygen conditions was an evolutionary spur for animals, will repeatedly reappear in this essay, as will . Ward’s hypothesis may be proven wrong or will not have the key influence that he attributes to it, but it also has plenty going for it. The idea that fluctuating oxygen levels impacted animal evolution has been gaining support in recent years, particularly in light of recent reconstructions of oxygen levels in the eon of complex life, called and , which have yielded broadly similar results, but their variances mean that much more work needs to be performed before on the can be done, if it ever can be. Ward’s basic hypotheses is that when oxygen levels are high, ecosystems are diverse and life is an easy proposition; when oxygen levels are low, animals adapted to high oxygen levels go extinct and the survivors are adapted to low oxygen with body plan changes, and their adaptations helped them dominate after the extinctions. The has a pretty wide range of potential error, particularly in the early years, and it also tracked atmospheric carbon dioxide levels. The challenges to the validity of a model based on data with such a wide range of error are understandable. But some broad trends are unmistakable, as it is with other models, some of which are generally declining carbon dioxide levels, some huge oxygen spikes, and the generally relationship between oxygen and carbon dioxide levels, which a geochemist would expect. The high carbon dioxide level during the Cambrian, of at least 4,000 PPM (the "RCO2" in the below graphic is a ratio of the calculated CO2 levels to today's levels), is what scientists think made the times so hot. (Permission: Peter Ward, June 2014)

I'm amazed by the varied experiences and life histories of our essay editing clients

For this essay’s purposes, the most important ecological understanding is that the Sun provides all of earthly life’s energy, either (all except nuclear-powered electric lights driving photosynthesis in greenhouses, as that energy came from dead stars). Today’s hydrocarbon energy that powers our industrial world comes from captured sunlight. Exciting electrons with photon energy, then stripping off electrons and protons and using their electric potential to power biochemical reactions, is what makes Earth’s ecosystems possible. Too little energy, and reactions will not happen (such as ice ages, enzyme poisoning, the darkness of night, food shortages, and lack of key nutrients that support biological reactions), and too much (such as , ionizing radiation, temperatures too high for enzyme activity), and life is damaged or destroyed. The journey of life on Earth has primarily been about adapting to varying energy conditions and finding levels where life can survive. For the many hypotheses about those ancient events and what really happened, the answers are always primarily in energy terms, such as how it was obtained, how it was preserved, and how it was used. For life scientists, that is always the framework, and they devote themselves to discovering how the energy game was played.

Energy and the Human Journey: Where We Have Been; …

A Guide to Isaac Asimov's Essays

Perhaps the most damaging deficiency in FE efforts, after self-serving orientation, was that the participants and their supporters were scientifically illiterate and easily led astray by the latest spectacle. Scientific literacy can help prevent most such distractions. While writing this essay, I was not only bombarded with news of the latest FE and alternative energy aspirants' antics, but I had to continually field queries regarding whether Peak Oil and Global Warming were conspiratorial elite hoaxes (or figments of the hyperactive imaginations of environmentalists and other activists), for two examples that readily come to mind. Digesting this essay's material should have those questions answered as mere side-effects. Far from being a hoax or imaginary, Peak Oil was and , and it is all downhill from there, and conventional oil will be almost entirely depleted in my lifetime. , although both were heavily promoted in the USA in 2014. In every paleoclimate study that I have seen, so-called greenhouse gases have always been considered the primary determinant of Earth's surface temperature (after the Sun), and carbon dioxide is chief among them. The radiation-trapping properties of carbon dioxide are not controversial in the slightest among scientists, and after the Sun's influence (which is exceedingly stable), declining carbon dioxide levels are considered to be the conditions that have dominated Earth for the past 35 million years. Humanity's increasing the atmosphere's carbon dioxide content is influencing the cause of Icehouse Earth, and , and are merely proximate causes. Increasing carbon dioxide can turn the global climate from an to a Greenhouse Earth, and the last time that happened, Earth had its . But have purposefully confused the issues, and a scientifically illiterate public and have played along, partly because believing the disinformation seems to relieve us all of any responsibility for our actions. Although scientific literacy can help people become immune to the disinformation and confusion arising from many corners, and reading this essay's first half can help people develop their own defense from such distractions, my goals for this essay's first half are far greater than that.