TOP 10 EXTINCTION EVENTS (SPECIAL MENTION)

 

But wait – there’s even more extinction events!

“Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a major extinction event, and the data chosen to measure past diversity”.

So more than enough for my usual twenty special mentions, although I don’t quite go so far as twenty extinction events, as I finish up with a few wilder entries – and start with a few more basic ones.

.Speaking of which…

 

(1) EXTINCTION

 

Well, you can’t have an extinction event without extinction!

So my first special mention has to go to the basic concept of extinction, which as it turns out is not so basic after all.

Coextinction, de-extinction, ecological extinction, extinct in the wild, functional extinction, extinction debt, extinction risk, extinction threshold, extinction vortex, latent extinction risk, local extinction, pseudoextinction, quasi-extinction – more than enough for their own top ten.

 

(2) EXTINCTION CAUSES

 

Of course, the Earth getting whomped by a whopping big asteroid will do it.

But apart from that…

As I said, you can’t have an extinction event without extinction – and you can’t have extinction without causes of extinction.

So my second special mention of extinction causes naturally follows from extinction itself as my first special mention – and it turns out that causes of extinction aren’t so basic either, particularly in the Holocene.

Climate variability and change, genetic erosion, habitat destruction, human impact on the environment, invasive species, Muller’s ratchet, mutational mayhem, overabundant species, overexploitation, overshoot, paradox of enrichment – more than enough for their own top ten.

 

(3) HUMAN EXTINCTION

 

For us, this would be the big one – THE extinction event.

You could also argue that it would be the last extinction event. Sure, extinction events would still happen – at least one in the next special mention – but unless another species evolved (or visited) to measure them, then they’d be like so that Zen tree falling in a forest with no one to hear it.

Of course, one might quibble with human extinction as an extinction event, given the former by definition is the extinction of one species, contrary to the high extinction rate of the latter.

Firstly, it’s like the old quip about the unemployment rate – the unemployment rate is 100% to you if you’re the one out of a job. Ditto human extinction for us with extinction rate.

Secondly, given contemporary humanity with its geographic spread and technological resources, I’d wager that any extinction event that can take us all out would have to take out a whole lot of other species as well.

The usual discussion about human extinction is the extent to which it would arise from natural risks – or anthropogenic ones of our own making. The consensus tends to be that the former involve relatively low risk of near-term human extinction, the latter not so much.

Anyway, human extinction is a subject that could have a top ten list of its own, although it largely overlaps one of my favorite recurring subjects that could have many top ten lists – apocalypse.

 

(4) FUTURE EXTINCTION

 

The Earth isn’t done with extinction events either – we know there will be a gauntlet of extinction events in the future, the last of which will ultimately involve a 100% extinction rate for any life living on the planet.

That’s not even including “random celestial events” that “pose a global risk to the biosphere, which can result in mass extinction” – impact by comets or asteroids, near-Earth supernova, and so on.

Of the more predictable long-term impacts, the most substantial is the steady increase in the Sun’s luminosity. In about half a billion years, that will result in atmospheric carbon dioxide falling below the levels required for photosynthesis and hence the extinction of plants.

Any life that does make it past then – presumably simple or microbial life – will face an uber-greenhouse effect with runaway evaporation of the oceans at about a billion years.

Any life that persists in the isolated pockets that remain remotely hospitable for it – at the poles, underground, and so forth – will face an increasingly impossible gauntlet of extinction that will be total at some point or other, whether when the whole planet surface essentially becomes a game of the floor is lava, or when the Sun expands enough to swallow it all up.

It’s a sobering thought to think that Earth only has a window of opportunity for complex life of about a billion years or so – and that we’re presently about halfway through it. At least, that’s what Peter Ward and Donald Brownlee propose in their book The Life and Death of Planet Earth.

Of course, a billion years is a long time, but it is only a small proportion – a twelfth or so? – of the planet’s duration, and even that is punctuated by numerous extinction events.

Even if humanity gets off the planet (taking whatever other life with it), other habitable planets have the same issue – and there’s an even bigger gauntlet of cosmic extinction events to run in the wider universe…

 

(5) BACKGROUND EXTINCTION

 

Extinction is kind of like the Hulk in The Avengers film – it’s always angry.

Extinction is always there as part of the natural evolutionary process – it just hulks out with a higher rate during extinction events. For example, our present Holocene extinction rates are estimated at 100 to 1000 times higher than the background extinction rate, hence qualifying the Holocene as an extinction event.

The background extinction rate is estimated on different scales but one such scale is the lifespan of species. Apparently, on average species typically exist for 5-10 million years before going extinct, but mammal species have a higher rate as typically existing for only 1 million years.

 

(6) SILURIAN – IREVIKEN, MULDE & LAU

(433 MILLION, 427 MILLION & 424 MILLION YEARS AGO)

 

And now we come to special mentions for actual minor extinction events – events that are classified as extinction events but not, ah, extinction-y enough for the Big Five (or Six). Because let’s face it – if it’s not one done by us, the one that killed dinosaurs, or the Great Dying, I mean who cares, really?

Anyway, there were these three minor extinction events during the Silurian Period – basically evolution gunning for the trilobites again. Oh – and other marine species I don’t really know.

 

(7) CARBONIFEROUS

(305 MILLION YEARS AGO)

 

Killing trees, I guess.

But seriously, it’s described as the Carboniferous rainforest collapse – in which rainforests fragmented and shrank from their former coverage, taking their flora and fauna with them.

 

(8) OLSON’S

(273 MILLION YEARS AGO)

 

Dress rehearsal earlier in the Permian Period for the Great Dying at the end – named for the person who identified the hiatus in the fossil record.

 

(9) END CAPITANIAN

(265-259 MILLION YEARS AGO)

 

Another dress rehearsal in the Permian Period for the Great Dying, by smaller volcanic eruptions (the Emeishan Traps) than the latter (the Siberian Traps).

 

(10) CARNIAN PLUVIAL

(234-232 MILLION YEARS AGO)

 

Climactic change event in the Triassic Period, with evolutionary winners and losers – among the winners were the dinosaurs.

 

(11) TOARCHIAN

(183 MILLION YEARS AGO)

 

Extinction event in two pulses during the Jurassic Period, with the second oceanic pulse as the larger one. Didn’t really affect the dinosaurs – or the Park.

 

(12) TITHONIAN

(145 MILLION YEARS AGO)

 

Another Jurassic extinction event towards the end of that period which didn’t really affect the dinosaurs or Park – minor and selective as extinction events go.

 

(13) APTIAN

(116-117 MILLION YEARS AGO)

 

Minor oceanic extinction event in the Cretaceous Period – didn’t really affect the dinosaurs.

 

(14) CENOMANIAN-TURONIAN

(93-94 MILLION YEARS AGO)

 

Minor oceanic extinction event in the Cretaceous Period. Didn’t really affect the dinosaurs – look, you need an asteroid for that.

 

(15) EOCENE-OLIGOCENE

(33.4-33.9 MILLION YEARS AGO)

 

“Large-scale extinction and floral and faunal turnover, although it was relatively minor in comparison to the largest mass extinctions” – in the Age of Mammals but mammals didn’t seem to be much affected.

 

(16) MIDDLE MIOCENE

(14 MILLION YEARS AGO)

 

Minor extinction event of terrestrial and aquatic life from global cooling in, you guessed it, the middle of the Miocene Epoch – more a disruption than an event, hence its alternative title of the Middle Miocene disruption.

 

 

(17) PLIOCENE-PLEISTOCENE

(2 MILLION YEARS AGO)

 

Apparently also known as the Local Extinction Bubble, hypothesized as a spike in extinction for some marine life from supernovae disrupting the ozone layer. Wait a minute – when did megalodon become extinct? (Spoiler – earlier, at about 3.6 million years ago)

 

 

(18) EXTINCTION MASCOT – DODO

 

Dead as a dodo.

Okay, I admit this isn’t really an extinction event, at least for everything else that wasn’t a dodo – it sure was an extinction event for them. As I quipped for human extinction, when you’re the one going extinct, the extinction rate is 100%.

In a sense, though, it was an extinction event for more than just the dodos. This poor flightless bird in the remote island of Mauritius had the unfortunate, unenviable and ultimately unrivalled distinction of becoming an extinction mascot – iconic of our human-driven Holocene Extinction. I suppose becoming extinct so dramatically will do that.

“The extinction of the dodo less than a century after its discovery called attention to the previously unrecognised problem of human involvement in the disappearance of entire species” – the dodo “has since become a fixture in popular culture, often as a symbol of extinction and obsolescence”.

 

(19) DECLINE IN AMPHIBIAN & INSECT POPULATIONS

 

The poster children of the ongoing Holocene Extinction, not least with respect to their own entries in Wikipedia.

I first became aware of the decline in amphibian populations from David Attenborough’s Life in Cold Blood, in which he attributed it to global warming, with their vulnerability in marked contrast to reptile populations.

I became aware of the decline in insect populations from reports of the decline of insect pollinators – no, not the bees! – and of the anecdotal windscreen phenomenon, as in fewer insects smeared on windscreens.

Lack of high profile attention has been attributed to the “comparative lack of charismatic species of insects” (as opposed to mammals and birds) but the insects most affected ARE the charismatic ones – bees, butterflies, moths, beetles, dragonflies and damselflies. (Cue the pun about damsels in distress). I mean, could it not be the insects people don’t like, such as flies or mosquitoes?!

And if we’re going to have a decline in insect populations, could we at least have a matching arachnid one?!

 

 

(20) FERTILITY DECLINE (STERILE INSECT TECHNIQUE)

 

I try to reserve my twentieth special mention for my kinky (or kinkier) entry where the subject permits, so I took that personally – as a challenge when it came to extinction events.

After all, I’m fond of quipping that my preferred cause of death would be from s€xual exhaustion, so why not expand that on a grand scale to cause of extinction? Ideally, extinction from s€xual exhaustion? Now there’s an extinction event I can get behind.

Less extinction events, more s€xtinction events, amirite?

While I could (disturbingly) imagine other s€xtinction events, not all of them as pleasant, the contemporary decline in human fertility was the closest I got, circling back to human extinction – that or the sterile insect technique used to control insect populations. Funnily enough, I learnt of the latter through its most famous example used as a title for James Tiptree Jr’s short story “The Screwfly Solution” – as a scenario of human extinction (from alien invasion).