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By the 1850s, Germany was , and seminal discoveries and achievements came from German labs. As agriculture became industrialized, two nutrients were identified as key limiting resources as per : phosphorous and . Until 1909, humanity’s source of nitrogen for agriculture was manure. Guano was even the main source of nitrate for gunpowder when World War I began in 1914. After a century of failure by many eminent chemists, in 1909 made one of history’s most momentous breakthroughs when he . That energy-intensive process is responsible for half of humanity’s food supply today. It is also partly responsible for a great deal of water pollution, , and proliferation of weaponry. Haber has also been called the father of chemical warfare, as he was instrumental in , but he nevertheless won his Nobel Prize in 1918 for his nitrogen breakthrough. Phosphorus, which forms the , is the sole element that humanity has not found a substitute for in industrial civilization. Energy makes nitrogen and other elements more available or allows for substitution, while phosphorous must be mined or recycled. German chemical wizardry continued after World War I, and Germany was the center of science in the early 20th century. Relativity and quantum theory, the two pillars of today’s physics, were developed in Germanic nations, and Einstein, , , , , , and dominated physics in the early 20th century, with relatively minor contributions from American, British, and French scientists. From the first Nobel prizes awarded in 1901 to the rise of Nazi Germany in 1933, more than a third of the awards in and went to Germans, and if the Swiss, Dutch, Austrian, Danish, and Swedish laureates are added, they amount to well more than half, particularly for their theoretical work.

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Of those , the most diverse is carbon, with that half-filled outer electron shell. Carbon provides the “backbone” for life’s chemistry, and is the foundational element of DNA, RNA, sugars, proteins, fats, and virtually all other components of life. Carbon can form and so forms the most diverse bonds with itself of all elements, and an entire branch of chemistry is devoted to carbon, called . Organic molecules are by far the largest known to science. During my first day of organic chemistry class, the professor observed that because the primary use of hydrocarbons was burning them to fuel the industrial age, we were living in “the age of waste,” as hydrocarbons are a treasure trove of raw materials. In the eyes of an organic chemist, burning fossil hydrocarbons to fuel our industrial world is like making Einstein dig ditches or making Pavarotti wash dishes for a living.

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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)

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This account was written in 1969 for publication in Marihuana Reconsidered (1971)

Sagan was in his mid-thirties at that time

Chemistry with Lab – Easy Peasy All-in-One High School

Thank you to Brenda Corrigan for her work on this course