The Sixth Extinction: An Unnatural History, by Elizabeth Kolbert

This is written by a Journalist using a story-telling style mixed with some reporting.

p.15, the same way acoustical engineers speak of “background noise” biologists talk about “background extinction”. One species to disappear every seven hundred years.

p.17, amphibians group’s extinction rate could be as much as forty-five thousand times higher than the background rate. It is estimated that one-third of all reef-building corals, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles and a sixth of all birds are headed toward oblivion.

p.45, nature does, on occasion, “change course”, and at such moments, it is as if the “thread of operations” has been broken.

p.61, Diminishing population density may have made survival less likely for the remaining individuals, a phenomenon that’s known as the Allee effect.

p. 69, and what was true for evolution should also hold for extinction, since according to Darwin, the latter was merely a side effect of the former. [some] animals had obviously not been done in by a rival species gradually evolving some competitive advantage. They had all been killed off by the same species [humans], and all quite suddenly over the course of Darwin’s own lifetime. Either there had to be a separate category for human-caused extinction, in which case people really did deserve their “special status” as a creature outside of nature, or space in the natural order had to be made for cataclysm, in which case, Cuvier was right.

p.80, Under high magnification, shocked quartz exhibits what look like scratch marks, the result of bursts of high pressure that deform the crystal structure. It was first noted at nuclear test sites and subsequently found in the immediate vicinity of impact craters.

p.96, A useful mnemonic for remembering the geologic periods of the last half-billion years is Camels Often Sit Down Carefully, Perhaps Their Joints Creak (Cambrian-Ordovician-Silurian-Devonian-Carboniferous-Permian-Triassic-Jurassic-Cretaceous). Most recent periods are: the Paleogene, the Neogene and the current Quaternary.

p.103, Evidence of the Ordovician glaciation has been found in such far-flung remnants of the supercontinent as Saudi Arabia, Jordan and Brazil.

p.104, Walter Alvarez: “we’re seeing right now that a mass extinction can be caused by human beings. So it’s clear that we don’t have a general theory of mass extinction.

p.113, If current trends continue, CO2 concentrations will top five hundred parts per million, roughly double the levels they were in preindustrial days, by 2050.

p.114, Thanks to all this extra CO2, the pH of the oceans’ surface waters has already dropped from an avergae of around 8.2 to an average of around 8.1. Oceans are now thirty percent more acidic than they were in 1800.

p.121, To build their shells or exoskeletons or calcitic plates, calcifiers must join calcium ions and carbonate ions to form calcium carbonate. Ocean acidification increases the cost of calcification by reducing the number of carbonate ions available to begin with. At a certain point, the water become positively corrosive and solid calcium carbonate begins to dissolve. Roughly one-third of the CO2 that humans have so far pumped into the air has been absorbed by the oceans, about 150 billion metric tons.

p.130, A trio of british scientists say: “it is likely that reefs will be the first major ecosystem in the modern era to become ecologically extinct.”

p.133, Caldeira calculated that a molecule of CO2 generated by burning fossil fuels will, in the course of its lifetime in the atmosphere, trap a hundred thousand times more heat than was released in producing it.

p.135, the first evidence that CO2 could kill a reef came from Arizone from the self-sufficient world known as Biosphere 2. A project that was considered a failure.

p.137, Corals grew fastest at an aragonite saturation state of five, slower at four and still slower at three. At a level of two, they quit building. Eventually, saturation levels may drop so low that Corals quit calcifying altogether, but long before that point, they will be in trouble because they are constantly being eaten by fish.

p.140, Darwin’s paradox has never been entirely resolved, but one key to the puzzle seems to be recycling. The Guadalupe Mountains in west texas are what’s left of the reefs from the Permian period. Reefs from the Silurian period can be seen in northern Greenland. Organisms that built reefs in the Cretaceous were enormous bivalves known as rudits. In the Silurian, reef builders included spongelike creatures called Stromatoporoids. In the Devonian, reefs were constructed by rugose corals, which grew in the shape of horns, and tabulate corals, which grew in the shape of honeycombs. Both these corals were only distantly related to today’s scleractinian corals and both orders died out in the great extinction at the end of the Permian. This extinction shows up in the geologic record of about 10 million years when reefs went missing altogether.

p.145, like the Jews, the corals of the Great Barrier Reef observe a lunar calendar. Once a year after a full moon at the start of the austral summer, they engage in mass spawning, a kind of synchronized group sex.

p.153, Temperatures in and of themselves lead to higher mutation rates. Thus, in the tropics, there’s been lots of time for diversity to accumulate. By contrast, as recently as twenty thousand years ago, nearly all of Canada was covered by ice a mile thick, meaning that every species of tree now found there is a migrant that’s arrived or returned just in the last several thousand years.

p.165, The number of species and the size of the area is not linear. It’s expressed by the formula S=cA^z where z is between 0.2 and 0.35.

p.167, on average, by 2050, 24% of all species would be headed forward extinction.

p.159, ways to calculate migration rates: by the number of trees or by their mass.

p.172, ‘biotic attrition’, a nice euphemism for extinction.

p.179, Islands are species-poor. Diversity drops off with isolation. A process that’s known as ‘relaxation’. Ecologists account for relaxation by observing that life is random. Smaller areas harbor smaller populations, and smaller populations are more vulnerable to chance. And small population is not confined to islands. In the absence of recolonization, local extinctions can become regional and then eventually global.

p.185, there are at least 2 million tropical insect species and perhaps as many as 7 million. By comparison, there are only about 10,000 sepcies of bird in the entire world, and 5500 species of mammals.

p.213, millions of years more, the biological world will become more complex again. Assuming that eventually travel & global commerce cease, the New Pangaea will begin to break up.

p.232, correlation isn’t causation.

p.238, humans had sex with Neanderthals. As a result of this interaction, most people alive today are slightly up to four% Neanderthal.

p.246, Europeans & asians shared more DNA with Neanderthals than did Africans. ‘leaky replacement’ hypothesis. Before mordern humans ‘replaced’ the neanderthals, they had sex with them. The liaisons produced children, who helped to populate Europe, Asia & the New World. All non-Africans from the New Guineans to the French to the Han Chinese, carry somewhere between 1 & 4% Neanderthal DNA. Humans are apes.

p.251, From archaeological records, it’s inferred that Neanderthals evolved in Europe or in western Asia and dispersed from there, stopping when they reached water or some significant obstacle. Archaic humans like Homo Erectus never came to Madagascar or Australia. Neither did the Neanderthals. Venturing out in the oceans was started by modern humans.

p.253, modern humans interbred with Denisovans too because contemporary New Guineans carry up to 6% Denisovan DNA.

p.255, One of the largest assemblages of Neanderthal bones ever found, 7 people, was discovered in southwestern France.