As scientists have been putting this picture together, one irony is that Cro-Magnons had black skin, and Neanderthals might have had light hair and eyes, as an adaptation to the cold climates that they lived in, as with Europeans today. It turns the racist aspect of on its head, and has been noted in some scientific corners. For the remainder of this essay, as all other human species were extinct but for the “hobbits” by 30 kya, the word “human” will refer to behaviorally modern .
What all early UP societies had in common was that although they formed in-group cohesion with their rituals, it also meant that were fair game, and the connection between religion and warfare precedes that migrating founder group, perhaps more than 70 kya. As will be discussed later, warfare and violence have been enduring human behaviors for the entire human journey, spanning from to today, with a brief hiatus when spread to open lands. , so that primate behavior probably has a history of tens of millions of years.
Ever since I was thrust into an soon after graduating from college, I became a student of wealth, poverty, and humanity’s problems. My of changing humanity’s energy paradigm have had a lifelong impact. It took me many years to gain a comprehensive understanding of how energy literally runs the world and always has. A good demonstration of that fact is to consider the average day of an average American professional, who is a member of and lives in Earth’s most industrialized nation. A typical day in my life during the winter before I wrote this essay can serve as an example.
That was a typical winter’s day in early 2013. During that day, around 80 times the calories that fueled my body were burned to support my activities. Those dying children often succumbed to hunger and diseases of poverty, and the daily energy that supported their lives was less than 1% of what I enjoyed that day. How did energy serve my daily activities? How did that disparity between the dying children and me come to be? This essay will address those questions.
Intense has existed in situations in which scientific and technological advances can threaten economic empires, but many areas of science are not seen as threatening, and reconstructing Earth’s distant past and the journey of life on Earth is one of those nonthreatening areas. I have never heard of a classified fossil site or a Precambrian specialist being threatened or bought out in order to keep him/her silent. There is more controversy with human remains and artifacts, but I am skeptical of popular works that argue for technologically advanced ancient civilizations and related notions. Something closer to “pure science” can be practiced regarding those ancient events without the threat of repercussions or the enticements of riches and . Much of this essay’s subject matter deals with areas in which the distortions of political-economic racketeering have been muted and the theories and tools have been unrestricted.
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.
Part of the hypothesis for skyrocketing oxygen levels during the late Proterozoic was that high carbon dioxide levels, combined with a continent that had been ground down by glaciers, and the resumption of the hydrological cycle, which would have vanished during the Snowball Earth events, would have created conditions of dramatically increased erosion, which would have buried carbon (the cap carbonates are part of that evidence) and thus helped oxygenate the atmosphere. Evidence for that increased erosion also came in the form of strontium isotope analysis. Two of strontium’s stable isotopes are . Earth’s mantle is enriched in strontium-86 while the crust is enriched in strontium-87, so basalts exposed to the ocean in the oceanic volcanic ridges are enriched in strontium-86 while continental rocks are enriched in strontium-87. If erosion is higher than normal, then ocean sediments will be enriched in strontium-87, which analysis of Ediacaran sediments confirmed. That evidence, combined with carbon isotope ratios, provides a strong indication of high erosion and high carbon burial, which would have increased atmospheric oxygen levels. There is other evidence of increasing atmospheric oxygen content during the late Proterozoic, such as an increase in rare earth elements in Ediacaran sediments. Although there is still plenty of controversy, today's consensus is that the Cryogenian is when , where they have largely stayed, although as this essay will later discuss, oxygen levels have varied widely since the late Proterozoic (from perhaps only a few percent to 35%).
Since the most dramatic instances of speciation seem to have happened in the aftermath of mass extinctions, this essay will survey extinction first. A corollary to is that if any critical nutrient falls low enough, the nutrient deficiency will not only limit growth, but the organism will be stressed. If the nutrient level falls far enough, the organism will die. A human can generally survive between one and two months without food, ten days without water, and about three minutes without oxygen. For nearly all animals, all the food and water in the world are meaningless without oxygen. Some microbes can switch between aerobic respiration and fermentation, depending on the environment (which might be a very old talent), but complex life generally does not have that ability; nearly all aerobic complex life is oxygen dependent. The only exceptions are marine life which has adapted to . Birds can go where mammals cannot, , for instance, or being , due to their . If oxygen levels rise or fall very fast, many organisms will not be able to adapt, and will die.
Mass extinction events may be the result of multiple ecosystem stresses that reach the level where the ecosystem unravels. Other than the meteor impact that destroyed the dinosaurs, the rest of the mass extinctions seem to have multiple contributing causes, and each one ultimately had an energy impact on life processes. The processes can be complex and scientists are only beginning to understand them. This essay will survey mass extinction events and their aftermaths in some detail, as they were critical junctures in the journey of life on Earth.
Around the end of that , another unique event transpired with enormous portent for life’s journey on Earth: one microbe enveloped another, and both lived. Today's prevailing hypothesis is that an archaean enveloped a bacterium, either by predation or colonization, and they entered into a . Today’s leading hypothesis, , is that the archaean consumed hydrogen and the bacterium produced hydrogen, which formed the basis for their symbiosis. That unique event transpired around two bya and led to complex life on Earth. That enveloped bacterium was the parent of all on Earth today, which are the primary energy-generation centers in all animals. About 10% of the human body’s weight is mitochondria. If not for the red of and the in skin, humans would look purple, which is the mitochondria’s color. That purple color is probably because the original enveloped bacterium that led to the first mitochondrion was .