E is for Extinction

The pop cultural perspective on extinction is filled with visions of failure. The extinction of the dinosaurs is frequently viewed through this lens. But consider the lengthy reign of dinosaurs on Earth. Dinosaurs spent more than 160 million years ruling Earth’s terrestrial ecosystems. And technically, when you consider those modern dinosaurs flying around today, it means that dinosaurs have been around for more than 230 million years.

Kristi Curry Rogers, “Dinosaurs.”

Dinosaurs are often used as the definition of old, dead, extinct. Blackberries are now dinosaurs. Baby Boomers are dinosaurs with modern devices. The moniker is somewhat unfair. After all, dinosaurs did spread and thrive across the globe longer than any other type of creature. Fish lasted for about 60 million years in the “Age of Fish,” and mammals have also only been around about 65 million years. Dinos are extinct, but it took a rather dramatic way to take them out. (Well, technically crocodiles have been around since the dinosaurs, so maybe…)

Still, for what it’s worth, before we get overwrought about dinosaurs disappearing and the horror of species vanishing, we should get straight how extinction actually works.

Two Flavors of Extinction

First off, there are two kinds of extinction:

• Background Extinction
• Mass Extinction

Species go extinct all the time, and they always have. Background extinction refers to a one-off event, where a species dies off because it can’t adapt to the existing conditions. They lose their habitat or food source. Predators adapt more quickly than they do. Climate change has occurred countless times across the earth, multiple ice ages and warm ups and volcanoes spewing sulfur and CO2, plants gobbling it up. Every time there is a significant climate change, species go extinct–we’ve already had two Ice Ages in human history.

In relatively recent history, species such as the dodo and passenger pigeon went extinct from human intervention. The dodo thrived on the predator-less island of Mauritius until humans showed up, both to hunt them and to introduce invasive species that hurt the dodos food supply. Passenger pigeons lived in huge flocks in the US and were hunted both for sport and because they devoured human farms. They went quickly, in part, because they were seen as prolific as they lived in large groups, but that also made them easier to wipe out.

But most species extinctions were not caused by humans, of course. Giant beetles, 50-foot crocodiles, and tiny horses are all also extinct, from the usual suspects. Change of habitat, lack of adaptation. Something else out-competed them. I don’t know about you, but I don’t want to be competing with a saber-toothed tiger. Or a Neanderthal, frankly.

Background extinction can be thought of as a one-off species elimination. One species out-competes another. The other type of extinction is much bigger: mass extinction. Mass extinction occurs when a cataclysmic event happens so large that it wipes out multiple species, or a huge portion of living species.

There have been several of these on earth, and paleobiologists have grouped them into the Big Five.

The Big Five

Geologists and paleobiologists have split time periods into groups and given them names: Devonian, Permian, Triassic, Cretaceous and so on. If you look at a geological time scale, the time periods are not marked out evenly (e.g. the Paleozoic and the Mesozoic are not the same span of millions of years). The demarcations come because there were huge changes in species and climate between one time period and another.

In each new time period, something big happens to change things more rapidly and cause a lot more havoc across the species. The Big Five changes happened. Our World in Data put together one chart with some of the details (the “Causes” text have been edited).

Extinction Event	Age(mya)	Percentage of species lost	Cause of extinction
End Ordovician	444	86%	Glacial/non glacial periods. Giant sea-level swings/change in ocean chemistry. Techtonic uplift as Pangaeia splits up. Sea life lost.
Late Devonian	360	75%	Rapid growth and diversification of land plants generated rapid and severe global cooling … and?
End Permian	250	96%	Intense volcanic activity in Siberia, CO2 and sulfur, acid rain… and ?
End Triassic	200	80%	Underwater volcanic activity in the Central Atlantic Magmatic Province (CAMP).
End Cretaceous	65	76%	Asteroid impact in Yucatán, Mexico. Maybe volcanoes, too.

Mass extinctions don’t necessarily happen in a week. Even the asteroid that ended the Cretaceous left effects across the planets that lasted for decades, probably hundreds of years. Scientists debate how long is long, but a thousand years isn’t that long when we’re talking about a geological layer.

So far, the biggest identified mass extinction, which killed off nearly all life, was at the end of the Permian, with all that volcanic activity. It definitely acidified the oceans. There were a few a key small survivors, notably early archosaurs and other reptiles. Some of them had mammal-like skulls and may have …eventually … spawned the first mammals. Others were the first dinosaurs. Reptiles that ran around on four legs but were upright. (In the picture, there’s a little dino running across the dead animal on the foreground, right).

Once the sulfur died down, the dinos had their shot. There was another mass extinction at the end of the Triassic, too, another bout of volcanic activity (maybe). The majority of dinosaur species at that time were reduced, but the ones that survived went on in the Jurassic and Cretaceous to become bigger and badder. All the time, of course, background extinction still existed. The Stegosaurus, one of the most recognizable dinosaur because of the bony plates across its back, was gone by the time T Rex showed up.

Extinction is a Process

We often see news stories today about various species going extinct and efforts to save a species. These should be approached with caution. Let me clear: it’s bad if humans hunt a species to extinction. It’s bad if humans wipe out a habitat that drives a species to extinction. We should avoid killing all the buffalo. Genocide–eliminating all of a species or an entire population–is bad. I’m right with the conservationists on those accounts.

But extinction is a little like death. It’s a natural process. We can’t save all species from extinction, nor should we. We really don’t want immortality, not for ourselves nor for other creatures.

And the focus on extinction is a little like focus on layoffs. The news always reports layoffs. It doesn’t report hiring. There is a natural turnover in employment, and there is natural turnover in species. There are new species discovered all the time. Some of the new species are discovered in the fossil records, creatures that lived a long time ago that we just now find out about.

New species are also discovered all the time, on earth. Some of these may be creatures we just never saw before, but some of them may be new new. One creature has gone extinct and another adapts and thrives by taking over its habitat. This guy from South America, just discovered last year, spits very gooey venom–could be a handy adaptation! Nearly 1000 new species were discovered, last year. Again, “new” might mean a previously-unknown extinct creature, but there are also new new critters.

Extinction of one creates opportunity for another. The dinosaurs flourished because other species disappeared. The mammals flourished when the dinosaurs disappeared.

How can they discover a new extinct creature? That’s the next post.