Tag Archives: mass extinction

The worst day in the history of the Earth

66.5 million years ago

This April 5 on Logarithmic History marks the most famous mass extinction ever, the one that did in the dinosaurs (okay, okay, the non-avian dinosaurs).

Just a few years back, we had news of one of the most extraordinary fossil discoveries ever, in North Dakota: a graveyard of fish piled on one another by a tsunami-like wave, and mixed with burned trees, and the remains of mammals, mososaurs, ammonites, and insects, and a partial triceratops, formed within hours of the asteroid impact that wiped out most life on Earth. Here is a news release, 66 million-year-old deathbed linked to dinosaur-killing meteor, and here is an article from the New Yorker, The Day the Dinosaurs Died.

The end-Cretaceous extinction isn’t the biggest ever, but it’s the one everybody knows about. The Disney movie Fantasia (1940) did a version of the event, set to Stravinsky (and mixing up Jurassic and Cretaceous dinosaurs). In Terence Malik’s movie The Tree of Life, a predatory dinosaur discovers compassion in an encounter with a hadrosaur just before all their kind are wiped out by an asteroid: mass extinction meets the Book of Job.

The discovery that dinosaurs (and about 70% of all species in total) probably went extinct as a result of an extraterrestrial impact did more than anything else to bolster catastrophism. For most of the history of modern geology, geologists have mostly argued instead for uniformitarianism: the same slow processes we see today caused past geological and evolutionary changes. When evidence for an impact was first discovered – a thin layer of iridium, presumably extraterrestrial — paleontologists were pretty uniformly hostile: no physicist was going to tell them how to do science. But by now the evidence is overwhelming that the asteroid impact that left the Chixculub crater, in what is now the Yucatan, was largely responsible for the end-Cretaceous extinctions (although the volcanic eruptions that created the Deccan traps in India may also have played a role).

But at the same time that evidence has increasingly vindicated the catastrophist position, new discoveries in paleontology have increasingly brought home that one group of dinosaurs survived the extinction. Most people think of birds and dinosaurs as two quite distinct kinds of animal. But birds are just as much dinosaurs as bats are mammals. Many dinosaurs had many of the distinctive features of birds – warm-bloodedness and high metabolic rates (probably), wishbones, an advanced respiratory system, feathers (sometimes brightly colored, sometimes used for courtship), and parental care for nests of eggs and juveniles. It’s even possible that some flightless dinosaurs, like the turkey-sized Caudipteryx, were secondarily flightless, descended from flying ancestors like Archeopteryx. We don’t have to hope for The Lost World or Jurassic Parkto come true to see living dinosaurs; a trip to the park, with The Sibley Guide to Birds (or appropriate guidebook for your region) in hand, will do it.

Amborella Day

The worst of times

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260 million years ago: the Capitanian mass extinction

A capsule summary of the evolution of life on Earth goes like this: There is steady progress in adaptation, driven especially by arms races, sometimes involving competitors, sometimes predators and prey. But this progress is interrupted from time to time by catastrophes – mass extinctions resulting from extrinsic causes, sometimes astronomical, but more often geological. (We’ll see much later in the year that a similar summary of human history goes like this: steady progress in the scale of cooperation driven by arms races, with occasional catastrophic interruptions, often associated with the spread of epidemic diseases.)

The geological causes of mass extinctions have been coming into focus lately. Many mass extinctions co-occur with the formation of Large Igneous Provinces (LIPS), regions where vast amounts of lava have flowed out of the earth, triggering a whole cascade of changes: the destruction of the ozone layer by halogen gases, global warming induced by CO2 and methane, and anoxic seas.

Large Igneous Provinces aren’t always associated with mass extinctions. What makes some episodes of massive lava flow particularly destructive is that they produce short circuits in the “planetary fuel cell.” The development of complex life has depended on the separation between an oxygen-rich, electron-hungry atmosphere and a reducing, electron-stuffed planetary interior. Some of the biggest setbacks to complex life have happened when lava flows from deep in the Earth’s interior punch through carbon deposits on their way up, and bridge this chemical gap between surface and interior.

The mass extinction 260 million years ago, the Capitanian, is not one of the classic five greatest mass extinctions, and has been overshadowed by the mother of all mass extinctions, the end-Permian, which happened just 8 million years later. But it took a major toll on living things, from marine organisms to dinocephalians. (The dinocephalians – more closely related to mammals than to dinosaurs, ranging up to hippo sized, and including both herbivores and carnivores – went entirely extinct with the Capitanian. See picture.) The Capitanian extinctions coincide with, and were probably caused by, the formation of the Emeishan LIP, now in southwest China.

A book published recently, The Worst of Times, pulls together the latest evidence that the Capitanian was the beginning of an 80 million year period in which mass extinctions were exceptionally common. Apparently the formation of the supercontinent of Pangaea and the Panthalassic superocean made living things particularly vulnerable to volcanically induced extinctions. Once Pangaea breaks up, mass extinctions are less frequent, and generally have different causes. The death of the dinosaurs had an extra-terrestrial cause, and the mass extinction we’re in the middle of results from the activities of one very unusual species.

Plagues and peoples

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210 – 309

Every day on Logarithmic History we cover an interval 5.46% shorter than the preceding day. From covering the first 754 million years after the Big Bang on January 1, we’re down to one century worth of history today.

And it’s a bad century for both Rome and China. Rome goes through an economic crisis, with a huge currency devaluation. Political life goes to hell too. From 235-284 there are 20 Emperors; 18 of them die violently. The Roman Empire experiences multiple, destructive invasions by barbarians. Previously under the Pax Romana, most of the cities of the Empire, including Rome, had been unwalled; now there is a spate of wall-building. The empire recovers toward the end of the century, but in a more heavily militarized and authoritarian form. And in China the Han dynasty disappears entirely after 220, to be replaced by three kingdoms of barbarian origin.

This coincidence of catastrophes may be more than just bad luck. Put it this way: If we look at the Big Picture, going way back on our calendar, and turning for a moment from human history to the evolution of life, we can summarize biological evolution since the Cambrian as:

A process of escalation, in which arms races among organisms are major drives of progressive evolution …

but …

Now and then, a physical catastrophe punctuates the history of life, causing mass extinctions, from which living things slowly recover.

Returning to human history, we can summarize social evolution since the adoption of agriculture as:

A process of escalation, in which conflicts between rival groups (matrilineal and patrilineal kin groups, empires, and – we will see – major religions) are drivers of increasing social complexity …

but…

Now and then, a biological catastrophe – in the form of an epidemic of some new disease – punctuates human history, causing major population losses, and often political and social collapse as well (i.e. the “germs” in Guns, Germs and Steel).

One such catastrophe contributed to the collapse of New World societies in the face of Old World diseases after 1492. But the Old World too must have had its own earlier catastrophes as the great killer diseases – the diseases of civilization that need a minimum population to keep going – established themselves.

Epidemic disease may have made a major contribution to the fall of Rome and of Han China. Rome suffered two massive epidemics, one from 165-180, another from 251-266. It’s plausible (and some day geneticsts will tell us whether it’s true or not) that these epidemics represent the arrival of smallpox and measles in the West. There is also evidence from the current distribution of tuberculosis strains that the expansion of the Roman Empire, and trade across borders, helped to spread this disease. And we’ll run into bubonic plague in a few days time (Saturday, October 13). There may be a similar story to tell about China, also stricken by epidemics at this time. The opening of the Silk Road and of trade across the Indian Ocean allowed precious goods and new ideas to travel between civilizations. It also opened the way for lethal microorganisms.

In addition to “Guns, Germs and Steel,” a classic book here is William McNeill’s Plagues and Peoples. For the Roman empire, more up-to-date, and with a wealth of information, is The Fate of Rome: Climate, Disease, and the End of an Empire.

Australian megafauna and the sixth great extinction

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40.1 – 38.0 thousand years ago

The Earth has been through a number of mass extinctions. On Logarithmic History, we covered the five greatest mass extinctions during the month of March, and into early April.

March 3. Ordovician/Silurian 440 mya
March 6. Late Devonian 364 mya
March 12. Permian/Triassic 251 mya
March 17. Triassic/Jurassic 214-199 mya
April 6. Cretaceous/Paleocene 65 mya

For all these extinctions, the most likely cause is some kind physical catastrophe: either drastic changes in the chemistry of oceans and atmosphere, or extraterrestrial events, like asteroid strikes or, just possibly, gamma ray bursts.

Competition with other organisms is another major cause of extinctions. Usually this is just part of a steady background level of extinction. But occasionally competition – and extinction rates – increase dramatically, as during the Great American Interchange five million years ago, when South American animals were swamped by North American invaders with the establishment of the Isthmus of Panama.

Earth now may be on the edge of another episode of mass extinction, a Sixth Extinction. (although rates of species extinction don’t match those of earlier ME’s. So far). This time the cause is very different: a single species, Homo sapiens, is playing an overwhelming role. Although the pace of extinction has accelerated over the last few centuries, you can make a case that the sixth extinction began a long time ago, with the expansion of modern humans out of Africa. Australia in particular sees the disappearance of a unique fauna that evolved over more than a hundred millions of years of isolation. This fauna included monster wombats, giant kangaroos, huge flightless birds, and a marsupial version of a lion.

All of these – all land mammals, reptiles, and birds with mass of more than 200 pounds – seem to have gone extinct by around 45,000 years ago, after humans crossed the sea to settle the island continent. (Sea levels were lower then, and Australia was connected with New Guinea, but still isolated from mainland Asia.) This is not settled science. Some researchers think climate change was to blame. But I think the evidence in the case of this and later mass extinctions is strongly in favor of humans as the major agent of extinction. This is one more reason to treat the advent of our species as one of the major evolutionary transitions, comparable to the evolution of complex cells, or multi-cellular life.

The worst day in the history of the Earth

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66.5 million years ago

This April 6 on Logarithmic History marks the most famous mass extinction ever, the one that did in the dinosaurs (okay, okay, the non-avian dinosaurs).

In memoriam, Paleozoic

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256 – 243 million years ago

Alfred, Lord Tennyson, wrote his poem “In Memoriam AHH,” in response to the death of his friend Arthur Henry Hallam. Several cantos consider the bleak lessons of paleontology – not just the myriads of deaths, but the specter of species extinction. Tennyson finished the poem in 1849, a decade before “The Origin of Species,” when the possibility of non-divinely-directed evolution and the reality of mass extinctions like the end-Permian were becoming part of general awareness.

Are God and Nature then at strife,
That Nature lends such evil dreams?
So careful of the type she seems,
So careless of the single life;

That I, considering everywhere
Her secret meaning in her deeds,
And finding that of fifty seeds
She often brings but one to bear,

I falter where I firmly trod,
And falling with my weight of cares
Upon the great world’s altar-stairs
That slope thro’ darkness up to God,

I stretch lame hands of faith, and grope,
And gather dust and chaff, and call
To what I feel is Lord of all,
And faintly trust the larger hope.

LVI

‘So careful of the type?’ but no.
From scarped cliff and quarried stone
She cries, ‘A thousand types are gone:
I care for nothing, all shall go.

‘Thou makest thine appeal to me:
I bring to life, I bring to death:
The spirit does but mean the breath:
I know no more.’ And he, shall he,

Man, her last work, who seem’d so fair,
Such splendid purpose in his eyes,
Who roll’d the psalm to wintry skies,
Who built him fanes of fruitless prayer,

Who trusted God was love indeed
And love Creation’s final law—
Tho’ Nature, red in tooth and claw
With ravine, shriek’d against his creed—

Who loved, who suffer’d countless ills,
Who battled for the True, the Just,
Be blown about the desert dust,
Or seal’d within the iron hills?

For one answer to Tennyson’s anguished question about human extinction, there’s an argument that says we can estimate how much longer humanity has got from just basic probability theory. It comes from astrophysicist Richard Gott, and goes like this: Homo sapiens has been around about 200,000 years. It’s not very likely that we’re living at the very beginning or very end of our species’ history, just like it’s not very likely that a name chosen at random from the phone book will come at the very beginning or the very end. Specifically, there’s only a 2.5% chance that we’re living in the first 2.5% of our species’ life span, and only a 2.5% chance we’re living in the last 2.5% of our species’ life span. So do the math, and there’s a 95% probability that our species will last somewhere between .2 million and 8 million years.

For more on Bayes’ Rule, and the future of humanity, here’s a recent book, The Doomsday Calculation.

The worst of times

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260 million years ago: the Capitanian mass extinction

Clovis and after

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13.0 – 12.4 thousand years ago

The Clovis culture lasts less than half a millennium. But it coincides with a major change in the North and South American fauna: specifically with a wave of extinctions of large animals. We’ve seen something like this before with the human settlement of Australia. There’s still controversy about the causes, but it seems likely that humans played a major role in both extinctions, even if climate change also mattered.

The mass extinctions caused by humans differ significantly from the five generally recognized earlier mass extinctions, which mostly seem to have resulted from physical disasters, like asteroid strikes and poisonous gases. A better analogy for human mass extinctions might be found all the way back at the beginning of the Cambrian period, 540 million years ago. Then, a relatively low-key, more-or-less predator-free fauna (the Ediacaran fauna) faced a devastating challenge from newly evolved, mobile, visually guided predators. The Human Revolution may come to rival the Cambrian Revolution in its biotic consequences.

Australian megafauna and the Sixth Great Extinction

3 Replies

The Earth has been through a number of mass extinctions. On Logarithmic History, we covered the five greatest mass extinctions during the month of March, and into early April.

Earth now may be on the edge of another episode of mass extinction, a Sixth Extinction. (although rates of species extinction don’t match those of earlier ME’s). This time the cause is very different: a single species, Homo sapiens, is playing an overwhelming role. Although the pace of extinction has accelerated over the last few centuries, you can make a case that the sixth extinction began a long time ago, with the expansion of modern humans out of Africa. Australia in particular sees the disappearance of a unique fauna that evolved over more than a hundred millions of years of isolation. This fauna included monster wombats, giant kangaroos, huge flightless birds, and a marsupial version of a lion.