[MUSIC]
The California Golden Bear The Great Auk
The Passenger pigeon The Tasmanian tiger
The Pinta Island tortoise The Golden toad
All dead. And the killer is right there in the room with you.
[MUSIC]
The walls of France’s Lascaux cave hold some of humankind’s earliest art, almost
mythical species: a wooly rhinoceros, enormous-antlered Megaloceros elk and massive aurochs. The artists
lived on, became us, but those cave walls are the last place that those animals still run. They’re
gone. Extinct.
We all pretty much understand extinction, it’s when a species kicks the proverbial
bucket, it rides off into the great biological sunset, bites the dust from whence it came
and shall return, which is all just a pretty way of saying that every last one of them
dies.
Even kids are used to the idea that sometimes groups of living things just… don’t exist
anymore. Okay, mostly don’t exist.
But extinction, as a thing, is a surprisingly new concept. In the 1790’s, by studying
various fossils, naturalist Georges Cuvier was the first to show that they were not from
living, yet undiscovered creatures, as many thought, but from what he called “lost species”.
In the decades to come, scientists like Charles Lyell and ol' Chuck Darwin began to popularize
the idea that Earth’s processes, like geology, evolution, and even extinction, did occur,
just very, very, verrrry slowly. So slowly that we’d surely never actually see something
go extinct. The idea of so-called catastrophic change was just impossible…
It wasn’t until the 1980’s that scientists were able to shake that idea. Geologist Walter
Alvarez was puzzled by the sudden disappearance of tiny aquatic fossils between two rock layers
that dated from about 66 million years ago, the same age as the last dinosaurs. With the
help of his Nobel Prize winning father, he analyzed the chemistry of that boundary and
found iridium levels that were off the charts. Now, there’s usually not much iridium in
Earth’s crust, but it’s very common in asteroids. So Alvarez’s theory? A 10-km
wide rock collided with Earth, wiping out 75% of Earth’s plants and animals. To be
honest scientists kinda laughed at it… until the 1991 discovery of the Chicxulub crater
near the Yucatan peninsula finally settled it.
Everything alive today is a descendent of a survivor of that terrible, horrible, no
good, very bad day, the so-called Cretaceous-Paleogene mass extinction event, the most recent of
the Big 5.
You should feel pretty lucky. When we look at all of Earth’s fossil record together,
98% of the species that have ever lived are extinct,. Only they haven’t always disappeared
at a constant rate.
In the history of life on Earth, we know of 5 different mass extinctions, when a majority
of life on Earth at the time disappeared in the blink of a geologic eye.
Besides the most recent dino-killer, there’s the Triassic-Jurassic, Late Devonian, Ordivician-Silurian,
and the worst of all, the End Permian. This was the mother of mass extinctions, it wiped out as many
as 96% of Earth’s species, so it got the best nickname: The Great Dying.
We’ve learned about all these just in time to get some bad news: We are in the 6th mass
extinction, and this time, we are the asteroid.
The hard facts of life mean that even when things are going pretty well on Earth, there’s
a background rate of extinction. Among mammals, for instance, we’d expect to see one species
go extinct every 700 years, or maybe one amphibian every thousand years.
Studies of current extinction rates say we’re roughly one thousand times past that, and
in some groups, like amphibians, are disappearing forty-five thousand times faster than normal.
And since there are so many species still unknown or uncharacterized, all of those numbers
are probably underestimates.
Goodbye, gastric brooding frog, Pyrenean ibex, the Fomosan clouded leopard. We could have
been friends.
So how do we know we’re to blame?
Around 13,000 years ago, as Earth thawed from its most recent big freeze, all of our favorite
weird megafauna like the wooly mammoth, Smilodon, and our old friend Megatherium disappeared
from the Earth, thanks to a changing climate and the invention of sharp stabby hunting
tools. I really wish we had saved the 8-foot long beaver though. That would be awesome.
Along the way, through hunting and farming, humans have been altering ecosystems in small
but significant ways, but since the Industrial Revolution, man we have really kicked it into
overdrive.
With the exception of maybe the first bacteria to breathe oxygen into the air, no living
thing has ever altered life on Earth to the degree that we have, which is why scientists
now refer to current epoch as the Anthropocene.
"We are the ultimate problem. There are 7 billion people on the planet, we tend to destroy
critical habitats where species live, we tend to be warming the planet, we tend to be very
careless about moving species around the planet."
According to a 2014 paper by Stuart Pimm in Science (link in the doobly do), the main
cause of the current extinction is human population growth and increased consumption. But those
two things lead to a whole mess of threats:
The most obvious are climate change and habitat destruction. Scientists found that most land
species have very small ranges, so they can’t just pack up and move when we cut down their
forest or turn it into a desert. Ocean species have more freedom to move to
better waters, unless they’re coral reefs, but thanks to the highest atmospheric CO2
concentrations in 800,000+ years turning the oceans more acidic, anything with a calcium
based shell has nowhere to run… or swim. If current trends hold up and the ocean hits
pH 7.8 by end of century, it could wipe out ⅓ of the species in the ocean.
Then there’s the invaders! Thanks to a species of snake hitching a ride on military cargo
in the 1940s, Guam has lost all of its native birds. "I have had it with these (invasive)
snakes on this (Guam-bound cargo) plane"
In Africa’s Lake Victoria, 100s of species of cichlid fish species vanished after fishermen
introduced the Nile Perch. Go us! We’re erasing species faster than we can
even name them. Stanford’s Rodolfo Dirzo says that in the past 40 years, invertebrate
populations, which might make up 97% of species on Earth, have declined 45% worldwide, and
that’s just the ones we know about. (Link in the doobly do to that one too)
You have to feel worst for the amphibians. Over the past 350 million years, they’ve
survived multiple mass extinctions, but this time we’re giving them all we’ve got.
Dirzo gives this loss of animal life a rather harmless sounding name: Defaunation. But there
is nothing cute about it. There is not a group of living things on Earth today that is not
threatened by the current and coming extinction. That includes us.
Extinction is about more than gorillas, tigers, polar bears, and rhinos, and the dozens of
other “famous” or “charismatic” species out there. Those are all important and worth
saving, but we need to care just as much about the humble beetles, the ugly little worms,
and the slimy frogs.
Every species, big or small, panda or protozoa, is important and worth saving, whether or
not we understand exactly why it’s worth saving.
John Muir once said, “When we try to pick out anything by itself we find that it is
bound fast by a thousand invisible cords that cannot be broken, to everything in the universe.”
I’ve put some links down in the description where you can get to know some of Earth’s
less-loved endangered species. Go make friends with one.
Our knowledge and understanding of the planet’s ecosystems may be incomplete, but our effect
on them knows no bounds. I hope the same tools and technology that we’ve used to push life
on Earth to the edge might also give us power to bring ‘em back.
So what are we gonna do? Let’s talk about it down there.
Stay curious.
If you want to read more about the brilliant and tragic stories of extinction in this age
of humans, check out "The Sixth Extinction" by Elizabeth Kolbert, link
in the description.