Tag Archives: mass extinction

The worst day in the history of Earth

66.5 million years ago

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). Here’s a link to a previous year’s post.

And just let year 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.

Amborella Day

207-196 million years ago

1 galactic revolution ago

The Triassic ends 201 million years ago with another major mass extinction (the fourth, by the usual count, after the end-Ordovician, end-Devonian, and end-Permian). Not quite as bad as the end-Permian (“only” 75% of species go extinct). This coincides with the formation of the Central Atlantic LIP (Large Igneous Province), which now includes a lot of eastern North America, northeast Amazonia, and western North Africa. So the end Triassic mass extinction may be the result of volcanoes spewing lava and carbon dioxide as Pangaea splits into Laurasia (North America, most of Eurasia) and Gondwanaland (South America, Africa, Antarctica, India, Australia).

The succeeding Jurassic Period will be when dinosaurs become the dominant vertebrates on land. The mammals around are mostly shrew-sized and nocturnal.

Not as conspicuous is another evolutionary innovation: the ancestors of Amborella, a rare shrub found in the wild only on New Caledonia, split off from the other angiosperms, ancestors of all other flowering plants, 200 million years ago. (This was suspected for a while, and confirmed in 2012 with the sequencing of the Amborella genome.) We can call this the origin of flowers. Amborella has clusters of small white flowers, with male and female separate.


Spring is gearing up in the Northern hemisphere; the honeybees have started to visit the earliest blooms on my apricot tree. If you’re lucky you’ll be able to smell the flowers on Amborella Day, and take your mind off catastrophes past and present.

In memoriam, Paleozoic

260 – 245 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.


‘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.

This might also explain the Fermi paradox – we, and other intelligent species aren’t likely to colonize the galaxy. But it’s only fair to add that a lot of other people (the physicist Freeman Dyson, for example) think this gloomily Tennysonian conclusion is an abuse of probability theory.

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

The worst of times

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.


Where is everybody? Maybe we’re (some of) the first

A followup to the previous post on the Fermi Paradox, some reasons the Universe could have been less suitable for the evolution of complex life until recently, making us one of the first intelligent species to evolve.

1) Metallicity. Chemical elements heavier than helium are formed inside stars, after the Big Bang. Elements heavier than iron are formed in exploding supernovas. These elements have been building up over time. Maybe they had to reach a threshold abundance to make complex life possible. Consider that in the “family tree” for the Sun, based on the concentrations of different elements, the Sun is the oldest member of its subfamily. Maybe it is only planetary systems associated with this subfamily that are well-suited for the evolution of intelligent life. And recent work suggests that phosphorus in particular may be a limiting and cosmically limited resource for the evolution of life.

2) Gamma Ray Bursts (GRBs). GRBs are bursts of gamma rays (high frequency radiation) lasting from milliseconds to minutes, like GRB 080319B. (Check out this tweet from January 11.) GRBs are probably supernovas or even larger explosions where one pole of the exploding star is pointed at the Earth. A major GRB could irradiate one side of the planet, and also affect the other side by destroying the ozone layer, causing mass extinctions. GRBs may have swept the Milky Way frequently in the past. The good news is they’re probably getting less frequent. This could be the first time in the history of the Milky Way that enough time has passed without a major GRB for intelligent life to evolve. If true, we should think about how to protect ourselves from the next one – lots of sunblock recommended.

If GRBs are such a threat, we might expect to find evidence that they have caused mass extinctions in the past (not wiping out all life obviously). For more on this, check out upcoming blog posts and tweets for the end-Ordovician, March 3.

3) Panspermia (life from elsewhere). Pretty much as soon as Earth could support life, we see evidence of single-celled organisms. Then life evolves slowly for a long time. The usual story about this is that the origin of life is easy, and it happens as soon as possible. But there is another possibility (illustrated below). It may be that the transition from simple replicating chemical systems to bacteria with genomes of tens of thousands of DNA base pairs is a slow process that happened over many billions of years somewhere other than Earth. Then newly forming planets in the nebula that gave rise to Earth were “infected” by this source, by meteorites carrying early cells. (It would have been easier for meteorites to carry life from star system to star system when the Earth was first formed than it would be today.) Back when our hypothetical “Urth” was forming, a billion years before Earth, there might not have been any planets with cellular life on them as potential sources of life-bearing meteorites.


Plagues and peoples


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:

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 …


  • 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.

Clovis and after

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.