Reading the Rocks

Marcia Bjornerud, 2005

Teaches at Lawrence University, Appleton, Wisconsin, on the north shore of Lake Winnebago. Professor of Environmental Studies and Geology. Has a unique casual writing style. Comes up with some eloquent portrayals of situations. The little details in the writing look like things she has put into practice in her classroom teaching.

xi Geologic time scale illustration

p1 Prologue: Stone Crazy

Interesting reflection on a bit of the history of the area, then a history of some of the major geological events discovered: clay, seabeds, buried forest, ryolite from volcano, granites with large crystals, followed by "other than that, nothing much has ever happened around here". Good intro to a casual, often humorous, and sometimes eloquent writing style. A gift for description.

p4 Earth as Accidental Diarist

p7 1. The Tao of Earth

p15 About half of sequestered CO2 is from marine organisms, CO2 negative feedback for climate stabilization essential, and life had a part.

p15 "Could the biosphere be the key to Earth's long-term equilibrium?"

p15-17 The best concise history of Lovelock's Gaia that I have seen.

p17 Lovelock's Gaia was pounced upon because it was teleological.

p17 Description of Daisyworld

p20 "Nothing is permanent, and yet because of this everything is eternal." I think this is the kind of language that attracted Denton to her. He has a number of quotes in "The Wonder of Water".

p21 Discusses extinctions, Snowball Earth 600-750myr, Permian-Triassic D2 crisis.

p22 Last paragraph quite eloquent catalog of human influences that change the "dance". We quite casually double or treble local rates of erosion --have increased phosphorus fluxes by 10 percent, CO2 additions 16 times that of volcanoes, 4 times faster than precipitation of carbonate rocks from seawater.

p25 2. Reading Rocks: A Primer

p25 Beautiful description of the "cacaphonous" effect of a stony beach to a geologist, concluding "So rocks are best observed at home ..."

p27 Reflection on James Hutton and his work on the strata on the coast, one almost level, the one below tilted ...

p28 Hutton's 1788 "The Theory of the Earth".

p28 Hutton died in 1797, birth year of Charles Lyell, who published "Principles of Geology" in 1833.

p29 Starts rock nomenclature - whole section useful for me to review for HyperPhysics.

p31 Big three shale, slate, schist - need to summarize in HyperPhysics

p33 Clastic like sandstone. Shale, sandstone, conglomerate in order of particle size.

p35 Good example of creative writing style. "So-called hard-rock (igneous and metamorphic) geologists sometimes scoff that the study of sedimentary rocks is akin to learning about trees by examining sawdust."

p36 Sandstone mostly quartz because of its durability in transport, while feldspars are the most abundant minerals.

p36 Search for rutile, tourmaline and particularly zircon. Good discussion of zircon's role.

p37 The famous western Australia zircon that dated to 4.4Gyr, about 150myr after the formaiton of the planet.

p38 Discussion of whether strata are mainly slow and long-term or mainly formed from major storms and unique events.

p38-39 Varves - Swedish term, fjords "hibernate" in winter, settling from clays in contrast to summer's active deposition. About 1cm thick, example of 13000 years of such strata.

p39 3.2Gyr tidal rhythmites, showing circular lunar orbit. 20.4 hour day at 1 Gyr past. "You just have to know the right rocks to ask."

p40-41 Section "Granite Planet". Mantle is 80% of Earth's volume, but volcanic material is very different from the mantle. Discusses fractional melting to produce the distinctly different composition of surface rocks. Mantle is Mg rich, Si poor.

p41 This fractional melting produces the basalt oceanic crust. Basalt is mainly pyroxene (Fe and Mg rich) and plagioclase (Ca - rich feldspars).

p41-42 Trend: increase Si, Na, K and sharp decrease in Mg. Parental mantle peridotite. peridotite -> basalt ->granite.

p42 Granite unique to Earth with K-feldspar and quartz.

p43 Existence of granite is evidence of long-term refining - a unique "tertiary crust".

p43 The primitive mantle rock is termed "mafic", Mg rich and Si poor (includes basalt) , and "felsic", Mg poor and Si rich (mantle, 'forgotten')

p43 "Only Earth has produced such a "tertiary" crust so unrepresentative of the bulk composition of the planet's interior."

p43 "Consequently, one of the first questions to pose to an igneous rock is where it falls on the spectrum from primitive, or mafic (magnesium-rich, silicon-poor), to evolved, or felsic (magnesium-poor, silicon-rich). A mafic rock like basalt generally has tales to tell of life in the mantle, while for a felsic rock like granite, whose progenitors were themselves crustal, the mantle is a nearly forgotten ancestral homeland."

p43-44 Use of trace rare earth elements for diagnostics. Check for what is missing, as a function of age.

p45 Limestones and shales as index minerals.

p46 Diamond is a "geobarometer", other crystals form at only specific temperatures and so are "geothermometers".

p48-49 Hutton story with interesting quotes. "abyss of time" and others.

p50 Mentions great unconformity in the Grand Canyon.

p51 Strong comments on the Cambrian Explosion and dismisses its "antievolution" flavor.

p52 Terms unique fossil beds as "jackpot beds" of low O2 sediment. Cambrian Burgess Shale - submarine mudslide. (?? didn't include the Chinese site.)

p54 Discussion of William Smith in the 1800s. William "Strata" Smith - canal digger - devised system of "index fossils" and the "principle of faunal succession".

p55 Discussion of the divisions of the Paleozoic, first the Cambrian and the Cambrian Explosion, than Mesozoic. Mesozoic start with 90% extinction of marine life, Jurassic period. Another mass extinction Cenozoic.

p56 Table 2.2 of Geologic time scale

p58 Radiometric dating

p59 Rhenium and osmium as part of geochronology.

p60 Discussion of precambrian

p61 4 Gyr Acasta gneisses of Canada

p62 Discussion of lunar rocks and the Hadean period

p65 3. The Great and the Small

p69 Discussion of Earth's "two hump" distribution with high mountains and deep ocean trenches. Basaltic melts low, "tectonically distilled" granite on the heights . Earth's crustal differentiation totally unique in the solar system.

p70 Other dynamic factors - water flowrate, groundwater permeability.

p71 Magnetic field

p73 Viscosity from water to lava

p74 Interesting example of salt as incompressible so that it becomes buoyant in slow motion at depth, leading to salt domes.

p74-76 Richter reflections, discussion of development of scale.

p79-83 Magnetic field and the bands of magnetic field reversal.

p79 10% drop in magnetic field in the past two centuries.

p80 Discussion of 1950s military towing of magnetometers which discovered the bands of reversed magnetic field.

p81 1963 Vine and Matthews modeling of magnetic field reversals, hundreds of reversals now documented

p82-83 SE Oregon evidence of rapid magnetic field change at 16Myr past, notes 780,000 years since last reversal.

p84 200,000 years of Greenland and Antartica ice caps

p85 From 18,000 years back to the year 1800 the CO2 about 0.004ppm, 1800 to present 0.6ppm, so over 150x

p86 Discusses the temperature proxies using O18 and O17 plus deuterium

p96 Discusses the End Permian and End Cretaceous extinctions and comments that no animals larger than cats made it through.

p99 4. Mixing and Sorting

p102 Elements Li (3) to Fe (26) are 10,000 times more abundant than those above Z=26

p103 It takes the pressure of 100 miles of rock to produce diamond from ordinary carbon.

p104 Discusses chondrites, named for tiny spherical grains called chondrules. In these chondrites, the proportions of the non-gaseous elements are virtually identical to the proportions of those elements in the Sun, so they are sometimes called "a piece of the Sun".

p106 Chondrules are found in anorthite, which is common on the Earth and Moon.

p107 The Allende meteorite found in Mexico is a chondrite, but has Mg26, whereas ordinary magnesium is Mg24. It looks like it started as Al26, a radioactive isotope with T1/2=730kyr. That places it close to the supernova that supplied isotopes to the Sun in both distance and time.

p109 Waxes eloquent about the planet forming process, with planetary accretion hindered by "slam-dancing rubble heaps", but "gravitational tidying-up won out over destructive acts of rogue rocks". Discusses Jupiter's sweeping up role.

p110 The evidence for Al-26 points to radioactive heat to melt planets to allow sorting. Then points to analog rocks, iron a nd achondritic stony meteorites which may come from shattered planetismals.

p111 Discusses Moon-forming collision model.

p112 Moon rocks very similar in O isotope ratios to the Earth, but there is no water on the Moon and it is higher in Ti and Fe.

p113 "Earth's stability and clemency" ... "And in almost every one of these transactions, water is involved as emissary, diplomat, shipper, and provocateur."

p114 "Only Earth developed habits of self-maintenance that have kept it looking youthful and fresh. Earth's beauty secret: Water, and lots of it." This eloquent quote was picked up by Denton in his Wonder of Water, p41.

p114 Discusses water in the silicate minerals called amphiboles and a list of others. Some maintain that Earth's water came from these types of minerals.

p115 Discusses comet delivery of water, some of it controversial.

p115 Water directly responsible for the generation of continental crust at subduction zones.

p116 Important page for describing what's happening at subduction zones and water's role in the processes.

p120 After discussion of the 180 Myr maximum age and about two dozen cycles, suggests that plate tectonics as currently viewed didn't occur on the very early Earth - maybe it started about 2.5Gyr. This is a new idea to me and I need to read this page more carefully. "This suggests that true plate tectonics, with rigid crustal slabs, efficient recycling of ocean crust via subduction, and water-assisted production of low-temperature melts, may not have occurred on the early Earth. Instead, plate tectonics could begin only when the Earth had reached a degree of thermal maturity, probably about 2.5 billion years ago (around the end of the Achaean eon and the beginning of the Proterozoic)."

p122 Still pegging 2.5Gyr as change point for plate tectonics. Uses Great Dike of Zimbabwe as indicator that rigid crust has begun to form. Dated at 2.5Gyr with the basalt that fills the crack.

p122-123 Raises the puzzle of evidence of plates at 3Gyr - talks about finding the mineral komatiite, a rock that could not form on the modern Earth because of its 1600C crystallization temperature. Some kind of primitive crust may have formed at a higher temperature than the current crust.

p124 Claims that water is a part of the solution to the puzzle. The start of a fairly detailed discussion of the tectonic recycling of the Earth's crust.

p124 Discusses "arc magmas" that are the future continental crust. The implication is that these are key constructs, but I need to read more about this idea. Discusses the formation of dense "eclogite", which is described as a combination of green pyroxene and red garnet. The idea I get is that this is the main material of the subducting plates and gives the high density that causes the sinking. But she discusses the fact that the water content is critical - that the driving out of too much of the water at the higher earlier temperatures led to lighter plates that might have been involved in the floating plates before 2.5Gyr.

p126 The section on "Waste Management" is rather detailed about how the eroded material from the surface gets into the subducting plates for recycling. This begins the discussion of the remarkable balance between crust formation and the erosion that brings the mountains down.

p128 "graywacke" and "flysch" are two names applied to the fairly uniform deposits from "turbidites". Turbidite seems to be an important concept and is discussed relative to sediment movement in the sea before subduction, but I just didn't get my head around all that.

p128-130 Reflections on the general balance of making and eroding crust. Discusses Be-10 dating (T1/2=1.6Myr) that suggests recycling time in the 10s to 100s Myr, but doesn't pin it down any more definitely than that.

p130 Gets down to expressing amazement with the efficient cycling of material by the Earth. It distills two types of crust. "All parts of the fabrication and recycling processes are cleverly linked and powered largely by water" "Water-facilitated melting" makes crust and "water-driven erosion" replenishes the mantle.

p131 "Efficient, sustainable, robust, and elegant, the system would win top honors in an industrial design competition." This was one of the quotes that Denton picked up on p57 of "The Wonder of Water".

p131 Jokes a bit about the unpredictability of the weather, but then counters with the fact that the overall annual pattern of both air and water movement is fairly predictable.

p131-138 Detailed and fascinating story of the "Snowball Earth" scenario which she dates between 750 and 600Myr. Details include glacial type sediments near the equator which are overlain with high carbonate deposits and banded iron - which makes for a lot of puzzles. Need to read this several more times.

p132 (1) The first evidence of "snowball earth" was the diamictites, disorganized sedimentary rock formations with two distinct populations of grain sizes - taken as a signature of deposition by glacial ice or laden icebergs. She lists some locations, but the problem was that these northern deposits had paleomagnetic signatures that suggested initial deposition at low latitudes - so ice near the equator?

(2) Just above the diamictites were deposits of carbonate rock and banded iron formations, both of which would have been presumed to be extinct at that time in history - expect them only in the 2.5-2gyr time frame.

p133 The "cap" carbonates were consistently found above the diamictites. That suggests that the oceans were oxygen depleted - they had to be for iron to go into solution. The banded iron formations indicate the restoration of oxygen and the precipitation of iron oxide.

p134 She actually studied the Svalbard diamictites as part of her PhD dissertation work.

p135 In trying to model the events it was suggested that maybe the oceans were sealed off by ice and volcanic productions of CO2 reached maybe 300x previous levels, producing potent acid rain. Such models scaled the time for the scenario to be about 10Myr, but it is questionable whether any life could survive that period.

p136 The other major proposal for the heating of the atmosphere is a major "planetary burp" of methane from ice gas hydrates. CH4 is 20x as effective as CO2 as a greenhouse gas, so that would shorten the time frame for the phenomena.

p136 What rocks do you ask? The cap carbonates have the kind of excess 12C over baseline that suggests biological origin. A counter proposal was that a long dead period in a capped-off sea would also give this kind of 12C manifestation.

p136-137 discusses the continuing debate:

CH4 -- faster -- explains 12C data with gas hydrate "burp"

CO2 -- 10myr -- explains 12C data with long absence of photosynthesis

p138 Discusses Rodinia, the predecessor to Pangaea. Possible snowball Earth contributor by straddling the equator and drawing out CO2 too quickly, cooling the Earth.

p138 Also interesting comments about negative feedback that kept previous glaciations from continuing to advance.

p139 Permean permutations. Discusses the great Permean extinction, which she places at 90% extinction compared to about 65% for the great K-T catastrophe. In the process, she blows right by the Cambrian explosion, consistent with her earlier minimization of that idea.

p139 "The late Permean extinction should scare us!" "This event remains one of the most frightening and least understood intervals in Earth's past."

p140 Pangaea spanned high and low latitudes, so glaciers did not advance very far out of the polar region.

p140 Extinction 252.3-251.4Myr, perhaps about 900,000 years for wiping out 90% of life.

p140 In analyzing possible contributors, the Siberian Traps have received a lot of attention. One of the largest volcanic events in the history of the Earth. Basaltic lava covered an area twice the size of Europe plus CO2, SO2, Cl, F to poison the atmosphere.

p140 Other flood basalt events include the Columbia River Gorge (15Myr), Midcontinent Rift Lake Superior (1.1Gyr) and the Deccan Traps of India (65Myr).

p141 A very scary page about the vast dead zone of the ocean

From Permean mudstones teeming with fossils to a black, barren, sulfurous, carbonaceous sediment with too little O2 for even scavengers to survive.

p141 There are modern dead zones in the Black Sea, Gulf of Mexico and Chesapeake Bay. Dense, salty bottom water prevents convective overturn for re-oxygenation.

p142-143 O2 isotope temperature proxies suggest 11F temperature rise. The late Permean carbon isotope ratio suggests a "belch" of methane because of the abrupt shift to isotopically light values.

p143 "The survivor profile is sobering; nothing larger than a house cat walked across the Permian-Triassic boundary, and the terrestrial ecosystem evidently did not full recover for as much as 5 million years."

p144 Her pessimistic reflection on some of the modern pollution scenarios.

p144-146 Describes a thin woody layer with remains of large trees with glacial evidence above and below. Worldwide cold period called Younger Dryas. Cold for about 1000 years after the beginning of recovery from the ice age. Attributed to a massive flush of fresh water that disrupted the "thermohaline ocean circulation", blocked Gulf Stream?

p147 "Understanding the rare times when Earth apparently lost its sense of balance makes the planet's general equanimity seem all the more remarkable."

p147 "Comparing Earth with it childhood peers, Mars and Venus, we see that even if a planet has all the raw materials, it will not necessarily develop a sustainable tectonic system, consistent climate, or long-lived biosphere."

p148 "But coupled in an intimate give and take, mixing and sorting - maelstroms and neatniks - form a potent creative team that has allowed the planet to maintain its vigor for 4 billion years."

p149 5. Innovation and Conservation

p150 In the biosphere, conservation is favored in times of stability, innovation in times of stress.

p150 The Paradox of Oxygen (Extremely well done - the best telling of this story that I have found!)

p150 Banded iron formations have been found in strata dated between 2.5 -2.0 gyr. They record the transition from CO2/H2O dominated atmosphere to an O2 dominated atmosphere. Before this, reduced iron was very soluble in sea water. But by the early Proterozoic era, photosynthesizing cyanobacteria "had been spewing out oxygen for at least a billion years." Only when the oceans were clear of oxygen-greedy iron could the gas begin to accumulate to significant levels in the atmosphere.

p151 "Red bands" of terrestrial sediment were oxidized iron components when they were deposited, so they flag the relatively mature state of the oxygen revolution. Quotes 1.8 gyr, but I'd like to know how it was dated since dating sediment is tricky.

p151 2nd paragraph eloquent. 3rd paragraph starts the mitochondria story.

p152 After discussing the challenges to the anoxic life forms which had been banished to anoxic environments by the oxygen revolution, she starts the story of the mitochondria.

"Alternatively, oxygen-unprepared organisms could remain at Earth's surface by forging alliances with those that had planned for the new world order. In a brilliant strategic merger, some early anaerobes assimulated mitochondria, which allowed the anaerobes to use oxygen as a metabolic fuel. The tiny mitochondria, in turn, received room and board (shelter and nutrients) from their hosts. Every cell in our bodies, and in every plant and animal on Earth, records this symbiotic union. Mitochondria re essential components of our cellular machinery - the respiration power stations where energy is extracted from glucose and made available for essential metabolic functions. ... Strangely, mitochondria have their own DNA, which is entirely separate from the host organisms own DNA, housed in the cell nucleus. (Because mitochondrial DNA is not mixed through the genetic exchanges that occur in sexual reproduction - it is inherited intact from one's mother - it conserves information about lineages. It has been used to infer when and where "Eve", the last common female ancestor of all modern humans,lived)."

p152 Paragraph 3, Lynn Margulis and endosymbiosis. Chloroplasts have similar roles in the plant kingdom.

p153 Discussion of cell nucleus as possibly a result of a merger, correlation with the mitochondria merger and appeared about the same time. Mentions 2.1gyr based on alga from banded iron formations.

p153-4 Discusses ozone and UVB. Pre-ozone organisms had to be experts at DNA repair.

p154 Discusses sexual reproduction with an element of mystery about how it started and persisted. I loved her line about the origin of sexual reproduction "The rock record is demurely quiet about this defining moment in the evolution of life .."

p155 pg2 "The lessons of the oxygen revolution would seem to be that it pays to anticipate change, as the mitochondria did, but when change is afoot, it is even more important to forge strong ties with able allies. In times of crisis, the most successful and versatile innovations can come from symbiotic cooperation, creative synthesis of acquired skills, and the free exchange of information."

p155 pg3 Stromatolites

p156 Beginning of multicellular organization. Evidence in the Proterozoic 1.2gyr with discussion of Australian crawler and red algae of Somerset Island, Canada.

p156 Discussion of acritarchs. At about 0.1 inch they were the monster life forms of their time and dominated the oceans for hundreds of millions of years, peaking at about 850Myr. Then the Snowball Earth nearly wiped them out.

p156 pg3 At about 570Myr the Ediacaran biota were in place

p157 In the location called Mistaken Point in Newfoundland there are well preserved Ediacaran fossils and zircon crystals that give a date of 570Myr.

p158 Points to a beginning of predation at about 540Myr which worked against the Ediacarans.

p158 Begins discussion of Burgess Shale

p158-159 Discusses Gould's "Wonderful Life" and Simon Conway-Morris. Discusses the Cambrian Explosion creatures, but reluctant to see them as all that revolutionary.

p159 Discusses Dawkins' view of the Cambrian Explosion in his 1990 review of Wonderful Life.

p160 Continues the discussion of the Cambrian Explosion pointing to the philosophical and political agendas involved. Uses the sentence "Some of the vehemence in the objections to Gould's ideas comes from the unflagging vigilance evolutionary biologists must maintain against creeping creationism."

p160 pg3 Discusses Gould's and Eldridge's "punctuated equilibrium".

p161 pg1 Expresses doubt about missing links. Discusses "radiations" after great changes like the Permian-Triassic and Cretaceous-Tertiary extinctions.

p161 Uses "ultra-Darwinists like Dawkins" and discusses the difference in perspective of geologists and biologists. Need to think about that more and go back and read this again.

p162 Good discussion of the difference between Gould and Conway-Morris. Comments on Conway-Morris' emphasis on "convergent evolution".

p162 pg4 Jumps in and bashes both Gould and Conway-Morris

p163 "An Orthopod-eat-Orthopod World" Seems to treat Cambrian Explosion as no big deal, relating all the creatures to orthopods. Describes the event as "that Cambrian day when the Burgess creatures happened to become entombed within a submarine mudslide."

p163 pg3 Finally acknowledges the Chengjiang fossil beds of China. Puts date of 520Myr vs last evidence of Ediacarans about 543 Myr. That puts Chengjiang earlier than Cambrian event.

p164 More discussion of predation and how it "changes the rules".

p164 Interesting reflection on "The Tragedy of the Commons" by W F Lloyd.

p165 pg2 "The early days of predation must have been remorseless. But this new world order also led to unprecedented innovations: not only protective shells and exoskeletons, but legs, backbones, eyes, and champion swimming. There was no turning back; life on Earth was irrevocably changed. Remarkably, the evolutionary innovations sparked by the early Proterozoic oxygen revolution and those in the Cambrian explosion have antipodal origins; in the first case, intimate collaboration; in the second, ruthless competition."

p165 The Many Legs of the Arms Race. "simply about tinkering with designs that had been established in the Cambrian"

p166 Quite a colorful reflection on the "arms race".

p166 An eloquent and far-reaching page. Need to go back and think about these things some more. Discussion of what is called the "Red Queen effect" in predator-prey relationships. The quote from Carroll's Through the Looking Glass is the Red Queen's words to Alice "in this place, it takes all the running you can do to stay in the same place". She talks about the development of better predator skills that are countered by the development of better defenses by the prey, so that a balance of predator-prey is established. "But the principle applies only to predators and prey that have evolved in the same relatively stable matrix .." and then she goes on to describe a number of pathological situations where the balance is disturbed - like poisoning a pest and thereby leading to a superior version of the pest, or antibiotics leading to the development of resistant species, or a plant or animal from distant shores in an environment where its natural enemies are absent.

p167 "In a natural system that has evolved over time, each creature has its nemesis; predator and prey, parasite and host are well-matched rivals. Ecosystems are tightly woven nets of coevolved species that cannot readily be dismantled, reassembled, or fabricated without serious consequences for the integrity of the whole."

p167 "Arms races in the geologic record always end, but never with victors. Instead, an external referee - a meteorite, an ice age, a methane belch - abruptly changes the criteria for fitness, and all the elaborate armaments and defenses so assiduously stockpiled become as useless as a credit card in the wilderness. Then it becomes a matter of finding new uses for the specialized machinery developed under the old regime."

p167 Communes and Junkyards

p168 Waxes eloquent about coral reefs and their long-term influence. Discusses plant kingdoms.

p169 Forest ecosystems of the carboniferous era about 350Myr

p169 At about 130Myr the partnership between insects and flowering plants developed. A tribute to the power of collaboration, there was an explosive diversification of insects. The plants involved in this collaboration, labeled angiosperms, took over from the more primitive gymnosperms so that now 99% of plants are angiosperms. And the number of insect species now exceeds the number of other life types combined.

p169 pg3 "Some innovations ... difficult .. without resorting to teleological .." The tone is to quickly distance herself from teleology and jump on the bandwagon of polyfunctionality as a bridge to evolutionary change.

p170 Seems to buy into "junk DNA" story, but does point toward some epigenetics.

p171 Something Old, Something New, Everything Borrowed

p171 Several interesting connections - collaboration vs competition, sex - makes possible more efficient experimentation evolutionarily, conservation and innovation are curiously entwined.

p171 pg4 "But no organism has ever evolved outside the rules of a physical and evolutionary environment." Seems like a curiously dogmatic statement about evolutionary biology for a geologist. She finally gets to a philosophical materialist manifesto.

p172 Very interesting final paragraph to this chapter. Reflects briefly on the nature of our consciousness. "For all of its potency, consciousness can become a pathological condition if it gives us delusions that we have somehow been exempted from the rules that have always governed the biosphere. The belief that we can engineer what evolution has done in 4 billion years - and expect the results to be predictable and controllable - is a sign of our youth and ignorance. Naive tinkering with such ancient systems is foolish, arrogant, and dangerous."

p173 6. Strength and Weakness

p173-176 Maybe her view of religion - a summary of a number of foolish religious projections on the geology and history of the Earth. I liked the tone of Montgomery's "The Rocks Don't Lie" better on this kind of summary.

p178 Sort of comes back down to Earth with discussion of Hutton

p181 Brings Lyell back into the discussion

p183 Reflects on Malthus, Darwin, Huxley

p184 Discussion of Rachel Carson's Silent Spring

p189 After several pages of philosophy, comes back to "multiple equilibrium states separated by narrow thresholds" and uses the thermohaline circulation system as an example.

p189 Discussion of climate modeling

p190 I think the last paragraph is quite eloquent on humanity's changing perspective of the Earth over the last 300 years.

p193 Epilogue: The Once and Future Earth

p194 "What do we know with any certainty? That we live on an old planet. That over geologic time, the face of the Earth has changed ceaselessly and yet on the whole has been a remarkably hospitable place. That Earth owes its unlikely equability to the balance of power between the commensurate forces of rock, water and life. That stability is favored by efficient recycling and a well-mixed atmosphere and hydrosphere, by a diverse biosphere with many interacting tiers, by cooperation and competition, by innovation and conservation." She continues with some comments on the extinctions, and on the dangers facing us from human activity.

p195 pg1 Amusing characterization of an environmental niche of a concrete-covered suburb: "a fast-growing environmental niche with plenty of opportunities for herbicide-resistant dandelions, supermosquitoes, and overgrown pigeons, raccoons, and rats with a taste for french fries."

p195pg 2 Eloquent parallel to Frankenstein

p195pg3 What will outlast us? '...three centuries of burning fossil fuels that had taken a half a billion years to accumulate"

p195 last paragraph, extending to p196 Beautiful reflection.

Ends with the story of she and her children witnessing a native american effort to stave off an environmentally disturbing mining project.

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