More than 99% of all species in the history of life on Earth are gone. Vanished from the face of the planet forever. But for much of human history, we didn’t even think animals could go extinct.

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Georges Cuvier was a naturalist, a zoologist, and he is considered the father of vertebrate paleontology, but most of all, he was a survivor.

When the French Revolution came sweeping through his country, upending centuries of monarchical rule, Cuvier escaped the worst of it, hidden away in a remote corner of France.

When Napoleon came to power, bringing an end to the revolution, Cuvier again survived, retaining his position as a professor of animal anatomy. When France’s armies came to a crushing defeat and Napoleon himself was exiled, Cuvier remained, spared the upheavals that killed so many of his fellow citizens and led to the disappearance of entire systems of thought that had reigned for centuries.

One of these systems of thought that was disappearing at the time was the idea that the Earth was changeless and perfect.

Since biblical times, people believed that God had created the Earth in a week’s time. Every ocean and continent, every animal and plant, and the ancestors of all of humanity were created in mere days — without exception and without error — just as they were today.

It was simply unthinkable for any one of God’s creatures to go extinct because that would mean somehow God’s creation had been imperfect.

Extinction not only seemed out of the question, it was blasphemy.

But in Georges Cuvier’s time this view was undergoing a revolution itself.

The bones of animals no living human had ever seen were being found in rockslides and at the bottom of coal mines all over Europe. While some of these fossils did bear some resemblance to familiar animals, some had no living counterparts.

And if a fossil seemed to have no living equivalent, the consensus was that it was merely the remains of an animal no one had seen yet, hidden away in some remote corner of the world.

This idea was so prevalent, President Thomas Jefferson had tasked explorers to bring back evidence of living American Mastodons — prehistoric elephants similar to Mammoths.

He was convinced they must be still alive somewhere in the uncharted American west.

Cuvier sought to overturn this idea, once and for all, by proving that these elephant bones were not of any living species. Through his detailed studies of both living and extinct animals, Cuvier would not only prove that Indian and African elephants were distinct species, he would prove that Wooly mammoths and American Mastodons were distinct species — without any modern counterparts.

Cuvier argued that these animals were much too big to have gone unseen, too conspicuous to have avoided detection. Cuvier went on to prove that many fossil animals were no longer around, including the bizarre Giant Ground Sloth and the massive sea going reptile, Mosasaurus, making the once unthinkable idea of extinction suddenly undeniable.

The concept of extinction may have been accepted by the scientific community but just what mechanisms caused an animal to disappear forever were still up for debate. Charles Darwin’s Theory of Evolution was still a few decades away, and while some scientists of the time tinkered with the idea that animals might change over time, Cuvier still believed that animals remained more or less the same as they always had been since the beginning of time.

Therefore, he reasoned, extinction must be brought upon by great and temporary changes in the Earth’s environment.

Planetwide catastrophes or “revolutions” as Cuvier preferred to call them.

Extinction was the natural consequence of these periodic upheavals and just as the French Revolution had led to the extinction of France’s monarchy and the archaic social systems that entailed, Cuvier’s revolutions led to the extinction of mammoths.

But some species managed to survive these upheavals and they either repopulated the vacant niches or remained where they were, untouched — just like Cuvier had during the revolution.

But with the discovery of evolution and natural selection, Cuvier’s theory of revolutions fell out of favor for more gradual theories of extinction. Extinction operated at the pace of evolution and species merely disappeared after long periods of slow decline.

And that was the way extinction was understood for a long time.

While scientists would hypothesize that global catastrophes might’ve been the culprit in mass extinctions, no evidence was found until the 1980s.

In the 1970s, geologist Walter Alvarez noticed that the only indication of the dinosaurs’ extinction was a thin layer of clay, beyond which no dinosaur fossils could be found. And this layer could be found all around the world. Walter could not for the life him understand how this thin layer of rock could contain the ingredients for the dinosaur’s extinction.

So he told his father about it.

Luis Alvarez was a Nobel prize winning physicist who not only discovered entire families of new particles, he worked on the development of the nuclear bomb and observed the bombing of Hiroshima and Nagasaki first hand.

With his father’s expertise, Walter discovered that this thin layer of sediment that marked the dinosaur’s extinction contained an unusual amount of iridium, an element rare on Earth but common in asteroids. They also found evidence of soot, shocked quartz crystals, and microscopic diamonds.

All indicative of a massive asteroid impact.

The extinction of the dinosaurs was a catastrophe of such destructive power it made the Hiroshima and Nagasaki bombs that Walter’s father designed look insignificant.

Despite all the evidence, the Alvarez hypothesis remained controversial.

It wasn’t until after Walter’s father’s death that an impact crater of the right size and age was discovered.

Since then, the Alvarez hypothesis has become accepted in the scientific community as the most plausible cause of the dinosaur’s mysterious disappearance.

Many more periods of mass extinction have been recognized in the earth’s history.

As many as twenty have been identified, but they are often grouped into 5 main extinction events, excluding the mass extinction that is happening right now, before our eyes, and at our behest.

Every day dozens of species are estimated to be lost forever. As many as 140,000 species may be lost every year and this loss is happening at a 1000 times the natural background rate.

Amphibians, birds, plants, fish, and invertebrates all have significant portions of their population at risk of disappearing from the planet. In the coming decades we could expect to lose up to a fifth of all mammal species. The African Elephant could soon vanish from the wild just as their ancient cousins — the mammoth and the mastodon — did thousands of years ago.

And instead of an asteroid this time, it’s us.

Habitat loss, environmental destruction, climate change, and rampant poaching have contributed to the greatest loss of biodiversity this planet has seen since the extinction of the dinosaurs.

And in millions of years, if there is anybody around to look at the strip of sediment that represents our time on this planet, they will be just as perplexed with the sudden disappearance of so many lifeforms as Walter Alvarez — except this time there will be no impact crater to validate his finds, only us.

Cuvier would’ve described this sixth mass extinction as a revolution. But unlike the French Revolution of his time, it is not being instigated in the name of liberty, fraternity, and justice. Instead today’s revolution is being fought in the name of short-sightedness, greed, and wastefulness. And it’s by these perverse ideals that those who survive will be irrevocably altered, and for those who don’t, the recklessness of their extinction will be permanently preserved in the geologic record.

But most of all, this extinction has been made possible through an insistent refusal to accept what Cuvier undeniably proved. Life on Earth is not limitless. In fact, it is exceedingly fleeting. And the world we live in cannot be taken for granted.

Because to truly understand extinction means we cannot be absolved of our own involvement in its execution.

For eons, since the beginning of the solar system itself, a chunk of stone the size of Mount Everest spiraled around the sun. Tiny perturbations in its orbit and minor collisions with other planetary bodies sent it closer and closer to its inevitable fate. It could not redirect its course any more than the dinosaurs could protect themselves from their impending doom.

While the trajectory of the asteroid had been set since its creation, the mass extinction happening today is not preordained. It’s not inevitable. It’s not written in stone. Not yet anyway.

It can be easy to despair in the face of problems this large — to see them as beyond our control and too impossibly entrenched to change. But it all begins with a revolution in ourselves.

Because what Cuvier proved was that the world could change, and that change could come suddenly and powerfully. A difference can be made.

While what we do on an individual scale might seem inconsequential, so can each perturbation in the orbit of an approaching asteroid. Every little wobble counts. And eventually it can be enough to make an impact.

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