The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and our Quest to Understand Earth’s Past Mass Extinctions. Peter Brannon. 2017

April – June 2023

Summary of Periods and Mass Extinctions

Edicarian: 635-538. First appearance of wide-spread multi-cellular organisms in ocean: Soft-bodied microbial organisms forming mats and other structures, and free-floating filter feeders.
End-Edicarian extinction: ~448. 86% species went extinct.* Possibly due to advent of burrowing organisms that disrupted largely sessile ecosystem. Not an official mass extinction because of a very incomplete fossil record.
Cambrian: 538-485. Warm shallow seas flank margins of several continental remnants of the breakup of the supercontinent Pannotia. In ocean there is the advent of hard-bodied complex organisms, and subsequent explosion of diversity into all phyla known today. The land bare except for microbial crust; arthropods and mollusks begin to adapt to life on land towards the end of this period.
Ordovician: 485 – 433. High CO2 levels and continents inundated with vast shallow seas jammed with life: brachiopods; trilobites; cephalopods; eurypterids; grapholites; and jawless fish. Many isolated continents and islands, with continents at south pole and a global sea occupying most of the northern hemisphere. First spores of land plants (fungi and simple plants) at 467Ma, with their spread possibly releasing phosphorous into the ocean stimulating algal blooms and CO2 sequestration.
End-Ordovician extinction:~345 Ma. 75% species went extinct.* Major ice age, likely precipitated by biogenic CO2 depletion, followed by a whip-lash of warming.
Silurian: 443-419. Gondwanaland and island chains provide diversity of environments; in the ocean early fish diversify into jawed and bony fish. Terrestrial life expands in the Silurian-Devonian Terrestrial Revolution: vascular plants emerge from more primitive land plants, and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized.
Devonian: 419-359. Gondwana supercontinent in the south, Siberia to the north, and Laurussia to the east. Free-sporing vascular plants form extensive forests (Archaeopteris); by the middle of the Devonian several groups have evolved leaves and true roots; by the end the first seed-bearing plants appear.
Late-Devonian extinction event: ~250 Ma. 96% species went extinct.* Two major extinction pulses, and many smaller pulses. One theory is that it is due to the release of nutrients by the punctuated spread of land plants as they developed vascular systems with leaves and roots, and seeds.
Carboniferous: 359-299. Age of amphibians — also first appearance of amniotes from which both reptiles and mammals came. Vast rainforests covered the land, and insects diversified. The latter part of the Carboniferous experienced glaciations, low sea level, and mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change
Permian: 299-251. On land: The Carboniferous rainforest collapse left behind vast regions of desert in the continental interior. Amniotes, which could better cope with the conditions, diversified into the synapsids (the ancestors of mammals which came to dominate the Permian) and the sauropsids (reptiles). . In the ocean fish diversify with placoderms dominating almost every known aquatic environment, alongside coeleocanths, with sharks and bony fishes on the sidelines.
End-Permian extinction: 251.9 Ma. 80% of species went extinct.* The Siberian Traps were created at 252 Ma and also interacted with the Tunguska sedimentary basin filled with carbonates, shale, coal and salt in layers up to 12 Km thick; it is the worlds largest coal basin. When the magma intersected the basin, it caught fire, detonated in multiple places, and released vast about of CO2 and methane, on top of the CO2 produced by the eruption contributing to global warming and ocean acidification and anoxia. Other chemicals produced by the incineration of the Tunguska basin contents may have destroyed the ozone layer.
Triassic: 252-201. Brannen argues for a long 5 – 10 million year recovery, but that is disputed. The ancestors of crodcodiles dominated the Triassic; ancestors of dinosaurs and first true mammals appear, but were not dominant. The global climate during the Triassic was mostly hot and dry. Pangea had deserts spanning much of its interior until ita began to gradually rift into Laurasia and Gondwana to the south. In line with this the climate shifted from hot and dry to more humid, with a massive rainfall event called the Carnian Pluvial Event that lasted a million years.
End Triassic Extinction: 200 Ma. 80% of species went extinct.* Volcanism from the rifting of Pangea produced flood basalt that covered more than 4 million square miles. The CO2 concentration doubled or tripled, raising the already warm temperatures by at least 3 ° C. The final extinction pulse was fast: on the order of 20,000 years.
Jurassic: 201.4 – 145. Gondwana begins to rift. Climate warm and humid.
Cretaceous: 145 – 66. Gondwana completes rifting and by the end of the period today’s continents are recognizable, but with shallow inland seas in North America and Africa and between Greenland and Norway.
End Cretaceous Extinction: xxx. 76% of species went extinct.* Most likely some combination of the eruption of the Siberian Traps and the Chixtulub impact lead to global warming and an extended period of darkness. Almost all large animals eliminated, including all dinosaurs excerpt ancestors of birds.

Percent of species that went extinct, for any one event, vary considerably among sources. These numbers are better read as an indicator of relative severity.

Introduction

A mass extinction is defined as any event during which more than half of earth’s species go extinct in less than a million years. There have been five such events during earth’s history. Many of these die-offs occurred within a few thousand years, and some were perhaps much quicker.

The three biggest mass extinctions have occurred within the last 250 Ma, and are associated with floods of lava on continental scales. Eruptions typically rapidly pump CO2 into the atmosphere, raising temperatures, and creating acidic, anoxic oceans. Earlier mass extinctions may, in contrast, have been due to the absorption of CO2 — possibly due to life, possibly due to weathering of volcanic rocks — which lowered global temperatures and precipitated global ice ages (aka. snowball earths). So, in summary, the five mass extinctions have all been associated with rapid changes to the earth’s carbon cycle.

If this book has a fault, it is that it focuses on the extinctions — as one would expect from the title — but often does not, to my eyes, give enough attention to the life forms and ecosystems that went extinct. For instance, for the End-Orodovician extinction, nothing is said about the state of life on land leading up to the event. As a consequence, I am adding summaries of the various periods between the mass extinctions, primarily drawing on Wikipedia.

If we are at the beginning of a new mass extinction, it is interesting to note that in the fossil record it would appear to have begun 50,000 years ago when humans spread out of Africa and wiped out all the megafauna. “Sometime they might say that the industrial spread of humans was just the coup de grace.“

Forgotten worlds spill from the sides of highways, beach cliffs, and from the edges of baseball fields, hiding in plain sight. … To see the world through the lens of geology is to see the world for the first time.
Peter Brannen, The Ends of the World, p. 8-9

From Wikipedia: https://en.wikipedia.org/wiki/History_of_life

C1: Beginnings: The Edicarian and Cambrian

The Edicarian*

* Content condensed from Wikipedia

The Edicarian spans 96 million years from the end of the Cryogenian Period 635 Ma to the beginning of the Cambrian Period 538.8 Ma. The supercontinent Pannotia formed and broke apart by the end of the period. The Ediacaran also witnessed several glaciation events, such as the Gaskiers and Baykonurian glaciations.

The Ediacaran marks the first appearance of widespread multicellular fauna following the end of Snowball Earth glaciation events, the so-called Ediacaran biota, which were multi-cellular but largely sessile organisms. Most of those organisms appeared during or after the Avalon explosion event 575 million years ago and died out during an End-Ediacaran extinction event 539 million years ago.

The Cambrian*

* Content condensed from Wikipedia

The Cambrian lasted 53.4 million years from the Ediacaran Period 538.8 Ma to the beginning of the Ordovician Period 485.4 Ma. Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.

The Cambrian marked a profound change in life on Earth: life diversified from a majority of soft-bodied unicellular, and came to include hard-bodied (mineralized), multicellular organisms gradually became more common in the millions of years. While these appeared gradually, the rapidly diversified in what is known as the Cambrian explosion, which produced the first representatives of all modern animal phyla.

Although diverse life forms prospered in the oceans, the land was comparatively barren with nothing more complex than a microbial soil crust and a few molluscs and arthropods (albeit not terrestrial) that emerged to browse on the microbial biofilm. By the end of the Cambrian, myriapods, arachnids, and hexapods started adapting to the land, along with the first plants.

From the book

Although not officially recognized as a mass extinction, the introduction suggests that the demise of Edicarian organisms around 540 Ma at the advent of the Cambrian explosion could be considered a mass extinction.

The chapter begins with fossils exposed at a Boston Beach. They look like concentric rings, and are about 500 million years old. While it is unclear when life originated, it likely dates back to around 4Ga. Eukcaryotes originated about 1.85 Ga.

Around 635 Ma there are signs of something more complex: traces of biochemicals likely produced by sponges. The marks the beginning of the Edicarian age (635 – 538.8) which lasted until the Cambrian at 538.8 Ma. The text in the book says that around 579 Ma, at the end of a global ice age (aka the third of three Snowball Earth periods), the fossil record reveals that large complex creatures appear on the ocean floor:

Across the windswept “hyperoceanic barrens” of southeast Newfoundland … is still more fossil graffiti left on old ocean rocks by these pseudo-creatures – hieroglyphic echoes of life in the perpetual midnight of the ancient deep. Some of the Newfoundland fossils recall fern fronds, feather dusters, and slender cones, while others appear as large, Seuss-like segmented slugs or bloated centipedes. They seem to have invented a way of life – a mostly immobile one – unlike anything live today: sluggishly sucking up organic gunk in the disgusting seas of the primordial earth across their membranes. […]
Around 540 million years ago, the Ediacaran world was destroyed – dramatically swept aside in the most important moment in the history of evolution: the Cambrian Explosion. When this spectacular supernova of biology detonated, the world of animal life – creatures that move around and eat other organisms for a living – was truly born. Though there are fossil whispers of an emergent animal lineage in the staid age that came before, the turbid seas had been dominated until then by the almost inert, fractal pseudo-creatures of the Ediacaran period. That all changed at the dawn of the Cambrian. Animals rapidly diversified and overthrew this weird life with a menagerie of even weirder life. Though it hasn’t been inducted into the ranks of the canonical Big Five mass extinctions, the Cambrian Explosion, counterintuitively, might have also marked the first such mass death in the history of complex life.
ibid., p 16-17

Wikipedia refers to an event called the ‘Avalon Explosion,’ at 575 Ma, during which many species appeared, eventually amounting to 270 species in 20 different genera. These Edicarian creatures only lasted about 33 million years before they were wiped out in the ‘Cambrian Explosion,’ at 538.3 Ma. There are a lot of theories about the cause of the Cambrian explosion, ranging from the advent of Oxygen to the development of vision. A particularly interesting one put forward in the book is that it is due to the evolution of organisms that burrowed, which stirred up the sea floor and destroyed the environment that the immobile Edicarian organisms depended upon for their nutrition.

The disappearance of the strange world that preceded the Cambrian Explosion — a zen garden world of unfamiliar fractal creatures rising from the seafloor and strange quilted blobs hugging the microbial mats — has long been a mystery to paleontologists.
But in 2015, Darroch and his colleagues declared the cold case to be a mass extinction. «We think of mass extinctions as requiring an abiotic driver: an asteroid impact or a period of volcanism. But here there’s strong evidence that biological organisms that changed their environment drove the extinction of vast swaths of complex, eukaryotic life. I think it’s a powerful analogy for what we’re doing today.” One new behavior in particular seems to have been responsible for much of the disruption: burrowing. The strange geometric creatures in Newfoundland and elsewhere depended on revolting, organic-rich murky seas, along with seafloors paved with undisturbed microbial muck, to survive. But when the Cambrian Explosion went off and animals inherited the earth, they began churning up the seafloor. For the strange quilted blobs of the former Ediacaran period that sat on the bottom and absorbed the nutrition from the placid sheets of slime, this was catastrophic. In fact, burrows in the rocks officially define the start of the Cambrian pe-rod for geologists.
ibid., p 19

With the Cambrian explosion life diversified XXXXX. The ocean of the Cambrian period “remained impoverished for millions of years as pulses of anoxic water intruded into the shallows, wiping out species after species in wave after wave of extinctions.” This period us referred to as the Cambrian Dead Interval.

C2: The End Ordovician Mass Extinction

The Ordovician

Ordovician spanned 55 million years, from 488 Ma to 433 Ma — it is sometimes termed”: “The sea without fish.” There were vast shallow seas — North America’s was less that a meter in depth on the average – in the interiors of continents, jammed with life: brachiopods; trilobites; cephalopods; eurypterids; grapholites; and jawless fish. Many isolated continents and islands, with continents at south pole and a global sea occupying most of the northern hemisphere. High CO2 levels existed throughout most of the period. First spores of land plants (fungi and simple plants) at 467Ma.

From the book

The global geography:

The End Ordovician Mass Extinction is the second most intense, eliminating XXXX.
Wikipedia on the EOME:

The Late Ordovician mass extinction is traditionally considered to occur in two distinct pulses.
The first pulse, known as LOMEI-1 began at the boundary between the Katian and Hirnantian stages of the Late Ordovician Period. This extinction pulse is typically attributed to the Late Ordovician glaciation, which abruptly expanded over Gondwana at the beginning of the Hirnantian and shifted the Earth from a greenhouse to icehouse climate. Cooling and a falling sea level brought on by the glaciation led to habitat loss for many organisms along the continental shelves, especially endemic taxa with restricted temperature tolerance and latitudinal range. During this extinction pulse there were also several marked changes in biologically responsive carbon and oxygen isotopes. Marine life partially rediversified during the cold period and a new cold-water ecosystem, the “Hirnantia fauna”, was established.
The second pulse of extinction, referred to as LOMEI-2, occurred in the later half of the Hirnantian as the glaciation abruptly receded and warm conditions returned. The second pulse was associated with intense worldwide anoxia (oxygen depletion) and euxinia (toxic sulfide production), which persisted into the subsequent Rhuddanian stage of the Silurian Period.

– Wikipedia

Notes on Ordovician from Thomas Halliday book: “During the Ordovician organisms began to adapt to life on land and, while still mostly microscopic, fungi and simple plants eroded continental surface rocks, releasing phosphorous compounds – rare in seawater – and stimulating algal blooms wherever they were washed on blown into the ocean. These blooms, along with volcanically-produced fresh silicates, resulted in the sequestration of carbon and the reduction in atmospheric CO2 (5600 à 3000 ppm), leading to the Hirnantian Glaciation, a relatively short event (500 Ma) which led to the only mass extinction due to global cooling.”
GOBE: Great Ordovician Biodiversity Event. Number of species tripled over 10 million years. Theories about causes of this include an increase in Oxygen (due to biogenic O2 production and CO2 sequestering), many islands that act as incubators, frequent meteor impacts (due to astronmical event at 467 Ma) that disrupted ecosystems and encouraged adaptation; and volcanism that produced a lot of C)2 and ash.
Interglacial periods: Few thousand years of warmth interspersed through 100,000 years of cold. (image below by By Dragons flight – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=184098)

Major ice age at end of Ordovician (445Ma) that lasted two million years. 5° C temperature drop likely due to biogenic sequestration of carbon and generation of oxygen, combined with a pause in volcanism. An ice cap formed on the south polar continent, which in turn lowered ocean levels and drained continental seas. Cooling also lead to turnover of deep water resulting in increased O2 levels that were probably not friendly to low-O2 adapted benthic life. In addition, the geography of the earth at that time provided little opportunity for animals to adapt by migrating north-south.

At the very end of the Ordovician the ice age ended with a whiplash of warming. The rocks showing evidence of glacial impact are capped with black shale, indicating an anoxic ocean, possibly due to silty glacial melt capping the ocean and stopping turnover (and light penetration), and extinguishing life forms that had adapted to higher oxygen.

… reading break …

C3: The Late Devonian Mass Extinction

The Silurian*

* Content condensed from Wikipedia

The Silurian spanned 24.6 million years from the end of the Ordovician Period at 443.8 Ma to the beginning of the Devonian Period at 419.2 Ma. The supercontinent Gondwana covered the equatorial regions and much of thesouthern hemisphere, and a large ocean occupied most of the northern hemisphere. The high sea levels of the Silurian and the relatively flat land (with few significant mountain belts) resulted in a number of island chains, and thus a rich diversity of environmental settings.

One important event was the establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution: vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized. Another significant evolutionary milestone during the Silurian was the diversification of jawed fish and bony fish.

The Devonian*

* Content condensed from Wikipedia

The Devonian spanned 60.3 million years from the end of the Silurian, 419.2 Ma to the Carboniferous 358.9 Ma. Devonian palaeogeography was dominated by the supercontinent of Gondwana to the south, the small continent of Siberia to the north, and the medium-sized continent of Laurussia to the east.

The first significant adaptive radiation of life on dry land occurred during the Devonian: free-sporing vascular plants formed extensive forests (Archaeopteris). By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared.

The first ammonites, a subclass of molluscs, appeared. Trilobites, the mollusc-like brachiopods, and globe-spanning coral reefs were still common. Arthropods, which had moved onto land from at least the Ordovician, became well-established early in this period.

Fish diversified, with the placoderms (Dunkleosteus, Bothriolepis) dominating almost every known aquatic environment, alongside coeleocanths, with sharks and bony fishes on the sidelines. We also see the beginning of land adaptation with pectoral and pelvic fins gradually evolving into legs (the chapter argues, perhaps hyperbolically, that this was driven in part by fear of the placoderms), though the tetrapods (e.g. hynerpeton) were not fully established until the Late Carboniferous.

From the book

The oil-rich black shale that is now a major source of petroleum in the US is from the end-Devonian extinction.
The Kellwasser Event. At 374Ma the first of two pulses of mass extinction destroyed 99% of the largest corral reefs the world has known (covering 3 million square miles, and order of magnitude more than we have today). It also annihilated coral reefs and numerous tropical benthic (seabed-living) animals such as jawless fish, brachiopods, and trilobites.
The Hangenberg Event. Fifteen million years later — at 359 Ma — a second extinction (global cooling) wiped out large predator – the armored placoderm fish – and nearly led to the extinction of the newly-evolved ammonoids.
In fact, although there were two major extinction peaks in the Devonian, there were a total of 10 over 25 million years.
An asteroid impact as the cause was proposed in 1969, at a time when mass extinctions were far outside scientific consensus thinking. This proved not to be the case for the Devonian extinction.
One theory for the cause of the extinction, advanced by Tom Algeo, is the development of roots and leaves by land plants. The argument is that roots enabled the retrieval of phosphorous from the soil, which was subsequently released into the water as plants died, resulting in a massive algal bloom that turned the oceans anoxic. This was exacerbated by the fact that the intra-continental seas had only narrow openings to the larger ocean.
It is possible that plant-triggered anoxia occurred in pulses: plants colonized certain areas of land, triggered a period of anoxia in the oceans, and then evolved mechanisms (e.g. seeds) that allowed them to spread into new niches on land, repeating the process.
The profusion of rooted plants also reduced CO2, in part by uptake by the plants (and sequestration of CO2 in the anoxia-generating algal blooms), and in part by the increased weathering caused by the effect of roots. The result was a 90% reduction in atmospheric CO2, which in turn lead to global cooling. “Each of the two largest mass extinction events in the Devonian were associated with sharp cooling and continental glaciation.“
The biogenic causes of the Devonian extinction are controversial. There is also evidence for extensive volcanic eruptions in Siberia, and ensuing global warming during the same period. David Bond argues that the cooling and anoxia post-dated the Kellwasser event, and that volcanogenic CO2 increases and ensuing warming and sea level rise brought the anoxic oceans of the Devonian surging into the intra-continental seas, triggered the first pulse mass extinction.
Evidence that plant evolution and anoxia triggered the Hangenberg Event is stronger: David Brezinski has found evidence — glacial erratics and dripstones — embedded in Devonian shales. This evidence points to a geologically brief but catastrophic shift to a glacial regime in the tropics at the end of the Devonian.
The end-Devonian extinction is the worst extinction for vertebrates, eliminating 96% of them.
Another puzzle about the end-Devonian is the lack of adaptation and establishment of new forms: normally, the rate of the appearance of new species increases during mass extinctions, but this was not the case in the end-Devonian. The text implies, but does specify, that invasive species were making ecosystems more homogenous and less diverse, and that this was exacerbated by the closure of ancient oceans as supercontinent formation proceeded. This seems vague.
With atmospheric CO2 levels bottoming out, we are at the beginning of the 100 Ma late Paleozoic ice age, the longest in the history of animal life.

C4: The End-Permian Mass Extinction

The Permian*

* Content condensed from Wikipedia

The Permian spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleozoic Era. Pangaea stretched in an arc from pole to pole, divided by a great mountain range where Euramerica and Gondwana had collided during the Carboniferous. Pangea was surrounded by the superocean Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior.

Amniotes, which could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors. During the Permian amniotes diversified into two groups: the synapsids (the ancestors of mammals which came to dominate the Permian, culminating in the therapsids) and the sauropsids (reptiles), giving us large land creatures roaming amidst forests. The ocean, its biosphere decimated during the last extinction, still had sharks and bony fish, and new reefs of sponges, horn corals and brachiopods had evolved, but overall it was still quite primitive.

From the Book

The End-Permian is the worse mass extinction that we know of: over 96% of species went extinct. In its wake, the ocean mostly reverted to slime and one species of clam (Claraia); and plankton largely disappeared, leaving a “chert gap” in the fossils record. On land, trees vanished for 10 million years leaving a “coal gap” in the fossil record; in the absence of surface cover and stabling roots, rivers stopped meandering and reverted to their braided form. All this happened quite quickly, within 60,000 years.
There was, briefly in the early oughts, a hypothesis that the End-Permian extinction was due to an impact event, but the consensus is now that that is not the case.
There were two smaller extinction events during the Permian: one called Olson’s Extinction, whose causes are mysterious; another due to a major volcanic eruption in China in the middle Permian.
There is a peak in light carbon at the time of the End-Permian. In part this may due to the mass destruction of the biome, which would release the light Carbon preferred by plants into the soil and air. But many think that more is required to explain the peak, which leads us to volcanism.
The Siberian Traps were created at 252 Ma. The eruption produced enormous quantities of CO2 (and flood basalts), and also interacted with the Tunguska sedimentary basin which had been accumulating sediment for hundreds of millions of years (since the Edicarian). The basin was filled with carbonates, shale, coal and salt in layers up to 12 Km thick; it is the worlds largest coal basin. When the magma intersected the basin, it caught fire, detonated in multiple places, and released vast about of CO2 and methane. To put this in context, if we burned all the hydrocarbons on earth we would release 5,000 gigatons of CO2; the incineration of the Tunguska deposit released between 10,000 and 48,000 gigatons of carbon.
In addition, the intersection of Siberian Volcanism with the sediments of the Tunguska basin also produced ozone-destroying compounds like halogenated butane, methyl bromide and methyl chloride. Evidence for the loss of the ozone layer can be found in the prevalence of malformed spores and pollen grains from sites around the world dating to the End-Permean.
The consequence of elevated CO2 — estimates of concentrations are typically around 8,000 ppm and go as high as 30,000 ppm — are warming (continental temperatures up to 140° F and equatorial ocean temperatures up to 104° F), oceanic acidification, acid rain, and oceanic anoxia.
Volcanism may also have released a lot of Hydrogen Sulfide, which is poisonous to most forms of life. One marker of the End-Permian extinction is a worldwide layer of isorenieretane, a pigment used in photosynthesis by a green sulphur bacteria that grows under conditions of no oxygen, Hydrogen Sulfide and sunlight.
Volcanism may also have produced sulphur blocking aerosols which would produce brief blasts of global cooling.
Stagnant oceans probably cannot exist, at least for long. Models suggest that differences in saliinity and undersea volcanism will kick circulation back into gear.
Lee Kump proposes that hypercanes — continental scale hurricanes with 500 mph winds (hurricanes currently exceed 200 mph) — are possible, according to models, when ocean temperatures exceed 100° F. Such hypercanes could also pick up CO2 and H2S and cross onto land, penetrating up the the poles.
Summary: hot anoxic acidic ocean suffused with H2S; Russian landscape suffused with lava and explosions the produce toxic, ozone-layer destroying gases; forest-destroying acid rain producing a rapidly weathering landscape that is so hot (140°) that even insects can’t survive; and hypercanes.
We are injecting CO2 into the atmosphere at 10x the rate as in the End-Permian, according to our best estimates.

… reading break …

C5: The End-Triassic Mass Extinction

The Triassic*

* Content condensed from Wikipedia

The Triassic spans 50.6 million years from about 252 Ma to 201 Ma. It began with an impoverished biosphere due to the massive End-Permian extinction and took 10 million years to recover, and 20 or more before it regained its former diversity. The ancestors of crodcodiles dominated the Triassic, and dinosaurs made their first appearance but did not become dominant until after the End-Triassic extinction. The first true mammals appear during the Triassic, but were not dominant.

The global climate during the Triassic was mostly hot and dry. The vast supercontinent of Pangaea existed until the mid- to late-Triassic, with deserts spanning much of Pangaea’s interior. Because a supercontinent has less shoreline compared to a series of smaller continents, Triassic marine deposits are relatively uncommon on a global scale. After Pangea began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south, with widespread faulting and rift basins. During this period its climate became more humid.

From the book

The relentlessly bleak conditions of the End-Permian — 140° F inland, and tropical ocean temperatures of 104° F – persisted for millions of years into the Triassic. Anoxia in the oceans persisted for 5 million years. The Wikipedia entry indicates that the persistance of poor conditions and slowness of recovery is a matter of dispute.
There is speculation that the existence of Pangea as a supercontinent, with its dry interior, meant that there was minimal weathering which in turn inhibited drawdown of CO2.
About midway in the Triassic — 20 Ma after the End-Permian – the climate shifted and it began raining in what is know as the Carnian Pluvial Event. It was extraordinary, but has received little study to date. It is suggested that this event was somehow kicked off by a flood basalt episode under the Triassic ocean , and/or the gradual move of Pangea to the north. [Don’t really understand how volcanism led to rainfall.]
By the late Triassic the ancestors of crocodiles were dominant; the ancestors of dinosaurs and mammals had also appeared on the scene.
The book suggests that the eastern coast of the US and the West Coast of Africa were adjacent in Pangea. This doesn’t go along with my understanding — I thought South American and Africa were once joined.
The rift valley that stretched across Pangea has remnants in the Hudson Valley (the Palisades), and many other places around the world in North Africa, Europe and the Amazon..
Volcanism from the rifting of Pangea is what ended the Triassic. It produced flood basalt that covered more than 4 million square miles. The CO2 concentration doubled or tripled, raising the already warm temperatures by at least 3 ° C. The final extinction pulse was fast: on the order of 20,000 years.
Coral reefs — the sort of reefs we know of today – were wiped out in the extinction, vanishing from the fossil record for 300,000 years.
Interesting: The same conditions that are good for preserving footprints are poor for preserving fossils.
A beautiful passage of fossil footsteps:

Unlike the plaster museum reconstructions of dinosaurs, which are often contorted in poses of theatrical menace, these footprints were utterly undramatic and prosaic. There was no pretense in these footfalls. This animal was utterly unaware of its place in the history of life. This was not a tableau of life in the Jurassic, but of life on a Tuesday afternoon. Here the footprints stop. There they resume in another direction. Here they break into a widely spaced jog, and there they narrow to a halt. These were actual moments of indecision recorded here in the rock-whims and lost trains of thoughts in the skulls of these unspeakably ancient animals as they prowled the shore. These were individuals, it struck me, each with its own personality and biography. I was unexpectedly encountering these personalities here, if only for a few moments- moments that the creatures themselves were blithely unaware would be preserved for all time.
– Peter Brannen, Ends of the World, p 172

… reading break …

C6: End-Cretaceous Extinction

The Jurassic*

* Content condensed from Wikipedia

The Jurassic spans about 56 million years from the end of the Triassic 201.4 Ma to the beginning of the Cretaceous Period, 145 Ma. At the beginning of the Jurassic, Pangaea had begun rifting into two landmasses: Laurasia to the north and Gondwana to the south. The climate was warmer than the present, and there were no ice caps.

On land, in the wake of the End-Triassic extinction, the fauna transitioned from the Triassic fauna, dominated jointly by dinosauromorph and pseudosuchian archosaurs, to one dominated by dinosaurs alone. The first birds evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards and the evolution of therian mammals. Crocodylomorphs made the transition from a terrestrial to an aquatic life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates. The first sharks, rays and crabs also first appeared during the period. Forests grew close to the poles, with large arid expanses in the lower latitudes.

The Cretaceous*

* Content condensed from Wikipedia

The Cretaceous spanned 79 million years from 145 Ma to 66 Ma.

Pangaea completed its tectonic breakup into the present-day continents, although their positions were substantially different at the time. Gondwana had begun to break up during the Jurassic Period, but its fragmentation accelerated during the Cretaceous and was largely complete by the end of the period. South America, Antarctica, and Australia rifted away from Africa (though India and Madagascar remained attached to each other until around 80 million years ago. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide that in turn created numerous shallow inland seas.

During the most of the Late Cretaceous, North America would be divided in two by the Western Interior Seaway, a large interior sea that receded late in the period. Africa was also split in half by a shallow sea, connecting the Tethys with the South Atlantic by way of the central Sahara and Central Africa, which were then underwater. Yet another shallow seaway ran between what is now Norway and Greenland, connecting the Tethys to the Arctic Ocean and enabling biotic exchange between the two oceans. At the peak of the Cretaceous transgression, one-third of Earth’s present land area was submerged.

The world was nearly ice free, though not quite as warm as the Jurassic, and forests extended to the poles. The oceans and seas were populated with now-extinct marine reptiles, ammonites, and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.

The book

There are twice as many species of birds as mammals — in a sense we are still living in the age of dinosaurs, which had dominated the world for the 200 million years of the Jurassic and Cretaceous, and come in every size and filled every niche.
Tyrannosaurs were human sized for 100 million years and on the sidelines; they only became big during the last 30 million years. They could see and smell very well, and could hear low frequency sounds.
Some time around 96 Ma some sort undersea eruption related to the rifting of India and Madagascar caused a smaller extinction event that cleared the way for the Tyrannosaurs
1980: Walter and Luis Alvarez publish paper presenting evidence for impact — iridium rich layer at the K-T (now K-Pg) boundary — event being cause of End-Cretaceous extinction. Later, discovery of shocked quartz and jumbled rocks suggesting tsunamis provide more evidence. And of course there is the discovery of the 60 miles diameter/ 20 miles deep Chicxulub crater suggesting the impact of an asteroid or comet that is miles in diameter. The impact would also have vaporized the sulfate rich carbonate bank of the Yucatan which could have produced sunlight blocking aerosols that would last for months.
Following the impact there would have been a fireball (seconds to minutes), ejecta falling all over the earth (within an hour), intense heat, seismic shaking at about 12 richter, and an air blast.
Modern birds are all descended from water birds, suggesting that their habit of living in burrows (and the impact happening in spring when they are on the nest) could be responsible for their survival.
Mayan cities are located along the rim of the crater remnant because the shock created denotes that provided accessible water.
Others disagree that Chicxulub impact is responsible for the extinction, They point to other large impacts leaving craters of 100-120 kilometers that appear to have little effect on life. Instead they point to the eruption of the Siberian traps — an eruption so extensive that it would cover the entire USA in lava 600 feet deep. They also point to global warming and ocean acidification.
Experts disagree as to whether the Deccan traps preceded the Chicxulub impact, or are contemporaneous. One theory is that the Chicxulub impact triggered the most intense period in the formation of the Deccan traps.

… reading break …

C7: The End-Pleistocene Mass Extinction

This is technically not a mass extinction, unless things get far worse in our future. The extinction discussed here is primarily the disappearance of 90% of large land animals that coincides very neatly with the spread of humans. It seems pretty clear that humans hunted a lot of large animals to extinction.

Overview of the Paleogene

In the Paleocene, the continents of the Northern Hemisphere were still connected via some land bridges; and South America, Antarctica, and Australia had not completely separated yet. The Rocky Mountains were being uplifted, the Americas had not yet joined, the Indian Plate had begun its collision with Asia, and the North Atlantic Igneous Province was forming in the third-largest magmatic event of the last 150 million years.

In the Paleocene, that average global temperature was 75–77 °F, compared to 57 °F in more recent times. The Earth had a greenhouse climate without permanent ice sheets at the poles and forests worldwide—including at the poles—but they had low species richness in regards to plant life, and were populated by mainly small creatures that were rapidly evolving to take advantage of the recently emptied Earth. Though some animals attained great size, most remained rather small. The forests grew quite dense in the general absence of large herbivores. Mammals proliferated in the Paleocene, and the earliest placental and marsupial mammals are recorded from this time, but most Paleocene taxa have ambiguous affinities. In the seas, ray-finned fish rose to dominate open ocean and recovering reef ecosystems.

The Paleogene spans 43 million years from the end of the Cretaceous to the beginning of the Neogene Period (66.0 – 23.03 Ma). This period consists of the Paleocene, Eocene, and Oligocene epochs.

Paleogene Paleogeography

During the Paleogene, the continents continued to drift closer to their current positions:

Australia had separated from Antarctica and was drifting toward Southeast Asia
The formation of the Antarctic Circumpolar Current significantly lowered oceanic water temperatures
Africa was moving north to collide with Europe and form the Mediterranean Sea
India was colliding with Asia forming the Himalayas
the Atlantic Ocean was widening
South America was moving closer to North America.
Inland seas retreated from North America early in the period.

Paleogene Climate

The global climate during the Paleogene – triggered in part by the formation of the Antarctic Circumpolar Current – began a cooling and drying trend that continued until the end fo the most recent glacial period. The trend was disrupted by warm periods:

the Latest Danian Event
the Paleocene–Eocene Thermal Maximum
and the Eocene Thermal Maximum

In particular the PETM was a major climatic event wherein about 2,500–4,500 gigatons of carbon were released into the atmosphere and ocean systems, causing a spike in global temperatures and ocean acidification. This upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals,.

Paleogene Life

In the first part of the Paleogene, the average global temperature was 75–77 °F (compared to 57 °F in more recent times) and the Earth had a greenhouse climate without permanent ice sheets at the poles. There were worldwide forests worldwide, but with low species richness in regards to plant life, and they were populated by mainly small creatures that were rapidly evolving to take advantage of the recently emptied Earth, including some that took to the oceans became modern cetaceans, and some that took to the trees became primates. Though some animals attained great size, most remained rather small. In the seas, ray-finned fish rose to dominate open ocean and recovering reef ecosystems. As the climate became cooler and more arid, there was a massive floral shift, and many extant modern plants arose during this time. Grasses and herbs, such as Artemisia, began to proliferate, at the expense of tropical plants, which began to decline. Conifer forests developed in mountainous areas.

Overview of the Pleistocene

The Pleistocene (often referred to colloquially as the Ice Age) spans the Earth’s most recent period of repeated glaciations from 2.58 Ma to 11.7 thousand years ago. The aridification and cooling trends of the preceding Paleogene were continued in the Pleistocene, and climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 meters lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by the Laurentide Ice Sheet.

Just before the advent of the Pleistocene, the previously isolated North and South American continents were joined by the Isthmus of Panama, causing a faunal interchange between the two regions and changing ocean circulation patterns, leading to the onset of glaciation in the Northern Hemisphere at about 2.7 Ma. During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia; the Late Pleistocene witnessed the spread of modern humans (and the extinction of all other human species) to the Australian continent and the Americas, co-incident with the extinction of most large bodied animals in these regions.

The Book

The cause of the PETM might have been undersea volacanoes in the North Atlantic burning through huge stores of fossil fuels
Another possible cause of the PETM is the subduction of seafloor carbonates during the India-Asia collision, and the emission of CO2 via volcanoes.
Later, as the Himalayas began to weather, the weathering could have drawn down CO2 and led to the cooling trend observed, mostly, throughout the later paleogene and the pleistocene.
In spite of various thermal peaks alternating with glacial periods, relatively few species became extinct, until half of large land animals became extinct at the same times that early humans moved out of Africa about 50,000 years ago. Large land animal extinctions also coincided with the later arrivals of humans into the Americas and Australia.
The anthropogenic extinction of large land animals is also supported by their continued survival on remote islands (giant ground sloths in cuba; wolly mammoths and Wrangle Island, etc.; Moas in New Zealand)
More recently, the anthropogenic incineration of hydrocarbons is releasing vast amounts of CO2 (“a superpower previously reserved for continental flood basalts”), and the fixing and subsequent release of nitrogen compounds via synthetic production of fertilizers is simulating the fertilization of the ocean, leading to phytoplankton blooms and subsequent anoxia.
Today only 3% of earths land mammals are wildlife; the rest are humans or their domesticated animals.
Reasons for hope, #1: We are nowhere near a mass extinction now (if we were, it would be too late)
Reasons for hope, #2: The geography of continental distribution is favorable: we have neither the Carbon-jamming supercontinent configuration, nor the scattered small continent configuration of the ordovician the prevented migration of organisms to more favorable environments during climate change.
Reasons for hope, #3: The oceans are as oxygenated as they have ever been, because phytoplankton have evolved to be larger and heavier, and thus the OMZ (Oxygen Minimum Zone) is deeper (600 meters), and will likely not trespass onto shallow continental shelves where it could cause mass extinction. [I’m unsure of why the OMZ is only at 600 meters down, and not from near the surface down to 600 meters.]

… reading break

C8 & 9: The Near Future & The Last Extinction

This is forward-looking and speculative, and as such doesn’t hold as much interest for me as the main part of the books. Nevertheless, here are a few notes:

Our ‘wet-bulb’ set point is 37-degrees celsius. This is the temperature above which mammals cannot survive, because their ability to keep themselves cool via evaporation of sweat fails.
In 2003 a heat wave killed 70,000 people in Europe. In 2010 a heat wave killed 55,000 people in Russia. In 2015 a heatwave in Karachi Pakistan killed 12,000 to 15,000 people. In 2015 a heatwave in India killed 2,500 people.
It is pretty much guaranteed that sea level will keep rising and ocean acidification will continue to increase for centuries.
One of the best urban candidates for being preserved in the fossil record is New Orleans. It is near a low point of a sedimentary basin…
Over geologic time, the sun is getting brighter and that in turn speeds up the weathering that removes CO2 from the atmosphere. The book argues that in 800 million years, the earth will be running low on CO2 and plants will go extinct (and at the same time it will be getting hotter and hotter).
There is an argument that our estimates of how often asteroid or cometary impacts occur on planets is biases, because planets that suffered higher impact rates are much more likely to lack observers. I’m a bit skeptical, because one should be able to infer impact regimes by looking at other planets and moons; I suppose if the argument is that our solar system is somehow lucky or sheltered, we’d need to wait until we can study other solar systems.