The Sixth Extinction

Book notes for "The Sixth Extinction", An Unnatural History by Elizabeth Kolbert

Quick review:

Great book. Reminds me of "Last chance to see".

I enjoyed the writing, and the fact that there are a list of sources and resources at the end of each chapter. The book feels deep and well structured while still being very readable. Full of fascinating facts and stories, I especially enjoyed the history of many theories we take as granted today, that were only proposed 200 years ago.

The rest of the book shows us how much we have already lost. It leaves you depressed and angry and frustrated. The book ends with a tiny note of hope. We are never good at predicting the future, it may well be that we are able to stop the trend. We could: stop eating meat (good chance?), use cleaner energy sources (very good chance?), reduce our footprint by living in more compact cities, reducing our road networks, restoring detroyed habitats (low chance?), have hugely more control over our environment thanks to new technologies (good chance?)

Questions raised:

What are we going to do about this! What can I do about this?

 Insights, lessons learnt:

We have already lost so much, and it may not be "fixable" on anything but geological timescales.


No creature has ever altered life on the planet in this way before, and
yet other, comparable events have occurred. Very, very occasionally in
the distant past, the planet has undergone change so wrenching that the
diversity of life has plummeted. Five of these ancient events were
catastrophic enough that they're put in their own category: the
so-called Big Five. In what seems like a fantastic coincidence, but is
probably no coincidence at all, the history of these events is recovered
just as people come to realize that they are causing another one.
location 70

(phrasing) Golden frogs have a distinctive, ambling gait that makes them
look a bit like drunks trying to walk a straight line. They have long,
skinny limbs, pointy yellow snouts, and very dark eyes, through which
they seem to be regarding the world warily. At the risk of sounding
weak-minded, I will say that they look intelligent. location 143

Until recently, when both of them went extinct, there were two species
of frogs, known as gastric-brooding frogs, that carried their eggs in
their stomachs and gave birth to little froglets through their mouths.
location 182

In ordinary times-times here understood to mean whole geologic
epochs-extinction takes place only very rarely, more rarely even than
speciation, and it occurs at what's known as the background extinction
rate. location 242

For what's probably the best-studied group, which is mammals, it's been
reckoned to be roughly .25 per million species-years. This means that,
since there are about fifty-five hundred mammal species wandering around
today, at the background extinction rate you'd expect-once again, very
roughly-one species to disappear every seven hundred years. location 246

One theory has it that Bd was moved around the globe with shipments of
African clawed frogs, which were used in the nineteen-fifties and
sixties in pregnancy tests. (Female African clawed frogs, when injected
with the urine of a pregnant woman, lay eggs within a few hours.)
location 283

Either way, the etiology is the same. Without being loaded by someone
onto a boat or a plane, it would have been impossible for a frog
carrying Bd to get from Africa to Australia or from North America to
Europe. This sort of intercontinental reshuffling, which nowadays we
find totally unremarkable, is probably unprecedented in the
three-and-a-half-billion-year history of life. location 289

In 1812, Cuvier published a four-volume compendium of his work on fossil
animals: Recherches sur les ossemens fossiles de quadrupèdes. Before
he'd begun his "researches," there had been-depending upon who was doing
the counting-zero or one extinct vertebrate. Thanks for the most part to
his own efforts, there were now forty-nine. location 562

> Before 1800s there was no concept of extinction! It was assumed that
> all animals that currently exist, still exist.

In fact, the American mastodon vanished around thirteen thousand years
ago. Its demise was part of a wave of disappearances that has come to be
known as the megafauna extinction. This wave coincided with the spread
of modern humans and, increasingly, is understood to have been a result
of it. In this sense, the crisis Cuvier discerned just beyond the edge
of recorded history was us. location 668

After the initial heat pulse, the world experienced a multiseason
"impact winter." Forests were decimated. Palynologists, who study
ancient spores and pollen, have found that diverse plant communities
were replaced entirely by rapidly dispersing ferns. (This phenomenon has
become known as the "fern spike.") Marine ecosystems effectively
collapsed, and they remained in that state for at least half a million,
and perhaps as many as several million, years. (The desolate post-impact
sea has been dubbed the "Strangelove ocean.") location 1204

On land, every animal larger than a cat seems to have died out. The
event's most famous victims, the dinosaurs-or, to be more precise, the
non-avian dinosaurs-suffered a hundred percent losses. location 1210

Everything (and everyone) alive today is descended from an organism that
somehow survived the impact. But it does not follow from this that they
(or we) are any better adapted. In times of extreme stress, the whole
concept of fitness, at least in a Darwinian sense, loses its meaning:
how could a creature be adapted, either well or ill, for conditions it
has never before encountered in its entire evolutionary history?
location 1255

> until us! We have broken free of evolution and are able to adapt using
> science/tech (up to a point)

In 1949, a pair of Harvard psychologists recruited two dozen
undergraduates for an experiment about perception. The experiment was
simple: students were shown playing cards and asked to identify them as
they flipped by. Most of the cards were perfectly ordinary, but a few
had been doctored, so that the deck contained, among other oddities, a
red six of spades and a black four of hearts. When the cards went by
rapidly, the students tended to overlook the incongruities; they would,
for example, assert that the red six of spades was a six of hearts, or
call the black four of hearts a four of spades. When the cards went by
more slowly, they struggled to make sense of what they were seeing.
Confronted with a red spade, some said it looked "purple" or "brown" or
"rusty black." Others were completely flummoxed. The symbols "look
reversed or something," one observed. "I can't make the suit out,
whatever it is," another exclaimed. "I don't know what color it is now
or whether it's a spade or heart. I'm not even sure now what a spade
looks like! My God!" location 1268

it revealed how people process disruptive information. Their first
impulse is to force it into a familiar framework: hearts, spades, clubs.
Signs of mismatch are disregarded for as long as possible-the red spade
looks "brown" or "rusty." At the point the anomaly becomes simply too
glaring, a crisis ensues-what the psychologists dubbed the " 'My God!'
reaction." location 1279

Even intense global warming and ocean acidification seem inadequate to
explain losses on such a staggering scale, and so additional mechanisms
are still being sought. One hypothesis has it that the heating of the
oceans favored bacteria that produce hydrogen sulfide, which is
poisonous to most other forms of life. According to this scenario,
hydrogen sulfide accumulated in the water, killing off marine creatures,
then it leaked into the air, killing off most everything else. The
sulfate-reducing bacteria changed the color of the oceans and the
hydrogen sulfide the color of the heavens; the science writer Carl
Zimmer has described the end-Permian world as a "truly grotesque place"
where glassy, purple seas released poisonous bubbles that rose "to a
pale green sky." location 1428

(A recent study of pollen and animal remains on Easter Island concluded
that it wasn't humans who deforested the landscape; rather, it was the
rats that came along for the ride and then bred unchecked. The native
palms couldn't produce seeds fast enough to keep up with their
appetites.) location 1463

Crutzen wrote up his idea in a short essay, "Geology of Mankind," that
ran in Nature. "It seems appropriate to assign the term 'Anthropocene'
to the present, in many ways human-dominated, geological epoch," he
observed. Among the many geologic-scale changes people have effected,
Crutzen cited the following: • Human activity has transformed between a
third and a half of the land surface of the planet. • Most of the
world's major rivers have been dammed or diverted. • Fertilizer plants
produce more nitrogen than is fixed naturally by all terrestrial
ecosystems. • Fisheries remove more than a third of the primary
production of the oceans' coastal waters. • Humans use more than half of
the world's readily accessible fresh water runoff. Most significantly,
Crutzen said, people have altered the composition of the atmosphere.
Owing to a combination of fossil fuel combustion and deforestation, the
concentration of carbon dioxide in the air has risen by forty percent
over the last two centuries, while the concentration of methane, an even
more potent greenhouse gas, has more than doubled. location 1493

The best explanation anyone has come up with for the end-Permian
extinction is a massive burst of vulcanism in what's now Siberia. But
even this spectacular event, which created the formation known as the
Siberian Traps, probably released, on an annual basis, less carbon than
our cars and factories and power plants. location 1712

The Great Barrier Reef extends, discontinuously, for more than 2,600
kilometres, and in some places it is a hundred and fifty metres thick.
By the scale of reefs, the pyramids at Giza are kiddie blocks.
location 1787

A paper published in Nature by the former head of the One Tree Island
Research Station, Ove Hoegh-Guldberg, predicted that if current trends
continue, then by around 2050 visitors to the Great Barrier Reef will
arrive to find "rapidly eroding rubble banks." location 1795

he once calculated that cutting down all the world's forests and
replacing them with grasslands would have a slight cooling effect.
(Grasslands, which are lighter in color than forests, absorb less
sunlight.) Other calculations of his show that to keep pace with the
present rate of temperature change, plants and animals would have to
migrate poleward by about ten metres a day, and 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. location 1825

It is estimated that at least half a million and possibly as many as
nine million species spend at least part of their lives on coral reefs.
location 1932

Honeybees warm themselves by contracting the muscles in their thorax.
Wood storks cool off by defecating on their own legs. (In very hot
weather, wood storks may excrete on their legs as often as once a
minute.) location 2204

It is now generally believed that ice ages are initiated by small
changes in the earth's orbit, caused by, among other things, the
gravitational tug of Jupiter and Saturn. These changes alter the
distribution of sunlight across different latitudes at different times
of year. When the amount of light hitting the far northern latitudes in
summer approaches a minimum, snow begins to build up there. This
initiates a feedback cycle that causes atmospheric carbon dioxide levels
to drop. Temperatures fall, which leads more ice to build up, and so on.
After a while, the orbital cycle enters a new phase, and the feedback
loop begins to run in reverse. The ice starts to melt, global CO2 levels
rise, and the ice melts back farther. location 2217

To use an extreme example, an island might be home to a single breeding
pair of birds of species X. One year, the pair's nest is blown out of a
tree in a hurricane. The following year, all the chicks turn out to be
males, and the year after that, the nest is raided by a snake. Species X
is now headed toward local extinction. If the island is home to two
breeding pairs, the odds that both will suffer such a string of fatal
bad luck is lower, and if it's home to twenty pairs, it's a great deal
lower. location 2499

In the nineteen-fifties and sixties, bird-watchers kept meticulous
records of every pair that bred on Bardsey Island, off Wales, from
common house sparrows and oystercatchers to much rarer plovers and
curlews. In the nineteen-eighties, these records were analyzed by Jared
Diamond, who at that time was working as an ornithologist, specializing
in the birds of New Guinea. Diamond found that the odds that any
particular species had gone missing from the island could be plotted
along a curve whose slope declined exponentially as the number of pairs
increased. Thus, he wrote, the main predictor of local extinction was
"small population size." location 2505

What distinguishes islands-and explains the phenomenon of relaxation-is
that recolonization is so difficult, in many cases, effectively
impossible. (While a land-bridge island may support a small remnant
population of, say, tigers, if that population winks out, new tigers
presumably aren't going to paddle over.) The same holds true for any
sort of habitat fragment. Depending on what surrounds the fragment,
species may or may not be able to recolonize it once a population has
been lost. location 2513

Army ants-there are dozens of species in the tropics-differ from most
other ants in that they have no fixed home. They spend their time either
on the move, hunting for insects, spiders, and the occasional small
lizard, or camped out in temporary "bivouacs." (Eciton burchellii
"bivouacs" are made up of the ants themselves, arrayed around the queen
in a vicious, stinging ball.) location 2546

around the turn of the century, Cryphonectria parasitica, the fungus
responsible for chestnut blight, was imported to the U.S., probably from
Japan. Asian chestnut trees, having coevolved with Cryphonectria
parasitica, were easily able to withstand the fungus, but for the
American species it proved almost a hundred percent lethal. By the
nineteen-fifties, it had killed off practically every chestnut in the
U.S.-some four billion trees. Several species of moths that depended on
the tree disappeared along with it. location 2832

Before Europeans arrived, New England had no earthworms of its own; the
region's worms had all been wiped out by the last glaciation, and even
after ten thousand years of relative warmth, North America's native
worms had yet to recolonize the area. location 2855

By transporting Asian species to North America, and North American
species to Australia, and Australian species to Africa, and European
species to Antarctica, we are, in effect, reassembling the world into
one enormous supercontinent-what biologists sometimes refer to as the
New Pangaea. location 2879

The process that turns an organism's long strands of DNA into
fragments-from a "text" into something more like confetti-starts pretty
much as soon as the organism expires. A good deal of the destruction is
accomplished in the first few hours after death, by enzymes inside the
creature's own body. After a while, all that remains are snippets, and
after a longer while-how long seems to depend on the conditions of
decomposition-these snippets, too, disintegrate. Once that happens,
there's nothing for even the most dogged paleogeneticist to work with.
"Maybe in the permafrost you could go back five hundred thousand years,"
Pääbo told me. "But it's certainly on this side of a million." Five
hundred thousand years ago, the dinosaurs had been dead for about
sixty-five million years, so the whole Jurassic Park fantasy is, sadly,
just that. On the other hand, five hundred thousand years ago modern
humans did not yet exist. location 3368

"Chimps do a lot of incredibly smart things," Michael Tomasello, who
heads the institute's department of developmental and comparative
psychology, told me. "But the main difference we've seen is 'putting our
heads together.' If you were at the zoo today, you would never have seen
two chimps carry something heavy together. They don't have this kind of
collaborative project." location 3441

It's only fully modern humans who start this thing of venturing out on
the ocean where you don't see land. Part of that is technology, of
course; you have to have ships to do it. But there is also, I like to
think or say, some madness there. You know? How many people must have
sailed out and vanished on the Pacific before you found Easter Island? I
mean, it's ridiculous. And why do you do that? Is it for the glory? For
immortality? For curiosity? And now we go to Mars. We never stop."
location 3467