Home2017-2018Humans force Earth into its sixth major extinction

Humans force Earth into its sixth major extinction

By Ben Newman
Guest Writer

The passenger pigeon, the Pyrenean ibex, the Caribbean monk seal, the great auk, the Tasmanian tiger, the Pinta Island tortoise, and the golden toad. All extinct due to humans.

The walls of France’s Lascaux cave display some of humankind’s earliest art, showing almost mythical species: cave lions, herds of wooly rhinoceros, and gigantic mammoths. The descendants of the artists lived on and became us, but outside those cave walls, those animals no longer run. They’re extinct.

In spite of the general public’s knowledge of extinct species, like the dinosaurs, extinction in itself is a surprisingly new concept.

In the 1790’s, by studying various fossils, naturalist Georges Cuvier was the first to reveal that fossilized remains were not from undiscovered biota, as many of his contemporaries thought, but from what he called “lost species.” Decades later, scientists such as Charles Lyell and Charles Darwin began to universalize the idea that Earth’s processes, namely geology, evolution and extinction, were constant, dynamic processes that occur over time, at a slow rate. So slowly, in fact, that we’d surely never actually see anything go extinct. The idea of a theoretical “mass extinction” was impossible until the 1980’s when scientists began to debunk that idea.

Walter Alvarez, one of the foremost geologists of the 1980s, was puzzled by the sudden disappearance of fossils from tiny aquatic organisms between two rock layers that dated from 66 million years ago. With the help of his father (Luis Alvarez), he analyzed the chemical composition of that boundary and found extremely high levels of an element called Iridium.

Typically, there’s little iridium in Earth’s crust. However, iridium is a very common element in asteroids. So how did it get there? Alvarez theorized that a 10 kilometer wide asteroid collided with Earth, wiping out about 75% of Earth’s plants and animals. At first, scientists were severely skeptical of this theory, that is, until the 1991 discovery of the Chicxulub crater near the Yucatan peninsula, which essentially settled the debate.

Everything alive today is a descendent of what survived that hugely destructive asteroid impact. The Cretaceous-Paleogene mass extinction is the most recent of the 5 mass extinctions.

It is known that 98% of species to ever exist on Earth are extinct. However, life on earth has not disappeared at a constant rate. In the history of life on Earth, we know of 5 different mass extinctions, where a majority of life on Earth (≥ 50% of genera, ≥ 75% of species) disappeared in the blink of a geologic eye. Besides the most recent, there’s the Triassic-Jurassic, Late Devonian, Ordovician-Silurian, and the worst of all, the End Permian. This wiped out as many as 96% of Earth’s species, and is nicknamed “The Great Dying.”

We are in the dawn of the 6th mass extinction, and this time– we are the asteroid.

The background extinction rate means that even when life is going relatively well, without any large fluxes in atmospheric or geologic cycles, there’s a normal rate of extinction. Among groups such as mammals, for instance, we’d expect to see one species go extinct every 200 years, or amongst a more ancient phyla –such as amphibians– we’d expect to see one go extinct every thousand years. Studies of current extinction rates say we’re roughly one thousand times past that in mammals, and in some groups, like amphibians, they are disappearing roughly thirty thousand to forty-five thousand times faster than their normal background extinction rate.

But how do we know we’re to blame? Well, around 13,000 years ago, as Earth thawed from its most recent big freeze, almost every species of megafauna: the wooly mammoth, smilodon and megatherium disappeared from the Earth, thanks to a changing climate and the mass expansion of humans, who had relatively recently invented hunting tools. Along the way, through hunting and farming, humans have been altering ecosystems in small but significant ways.

Furthermore, according to a 2014 paper by Stuart Pimm in “Science,” the main cause of the commencing extinction is human population growth and increased consumption. But these two things lead to a whole host of other problems: the most obvious of these are climate change and habitat destruction. Scientists have found that most land species have relatively very small ranges — such as the Iriomote cat, for instance — and thus, can’t move with ease and find “greener pastures” when we cut down their forest or turn it into a desert.

For oceanic species, the outlook doesn’t look much better. Thanks to the highest atmospheric CO2 concentrations in 800,000+ years, we’re turning the oceans more and more acidic and any organism with calcium carbonate based parts (especially corals) are being wiped out of the food chain purely due to lack of habitable pH ranges, not to mention overharvesting.

According to current trends monitored by NOAA, if the ocean hits pH 7.8 before the end of century, more than a third of the species in the ocean would be wiped out.

Then there’s invasive species. Thanks to a species of snake (brown treesnake) hitching a ride on a U.S. military cargo plane in the 1940s, Guam has lost all of its native birds. In Africa’s Lake Victoria, hundreds of endemic species of cichlid fish species vanished after fishermen introduced the Nile Perch in the 1950s. We’re wiping out species faster than we can even identify them. Stanford’s Rodolfo Dirzo says that in the past 40 years, invertebrate populations, which might make up a total of 97 percent of species on Earth, have declined 45 percent worldwide.

The most tragic case has to be that of the amphibians. Over the past 350 million years, they’ve survived multiple mass extinctions. However, because of human-caused perturbations — encroachment of chytrid fungus, dumping of pollutants into waterways and increased pesticide use–one-third of the nearly 6,300 known amphibian species are threatened to become extinct.

Extinction is about more than just widely known species. Every species, big or small, panda or protist, is important and worth saving whether or not we currently understand exactly why it’s worth saving.

John Muir 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.” Our knowledge and understanding of the planet’s ecosystems is far from complete, but our effect on them knows no bounds. Technologies and policies we’ve created can be made to meet the needs of biota worldwide. The same developments that we’ve used to push many species to the edge could give us the power to not only conserve, but restore what has been lost.

 

bfnewman@willamette.edu

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