If we use the same approach to estimate today's extinctions per million species-years, we come up with a rate that is between ten and 10, times higher than the background rate. Even considering a conservative background rate of two extinctions per million species-years , the number of species that have gone extinct in the last century would have otherwise taken between and 10, years to disappear if they were merely succumbing to the expected extinctions that happen at random.
This alone supports the notion that the Earth is at least experiencing many more extinctions than expected from the background rate. It would likely take several millions of years of normal evolutionary diversification to "restore" the Earth's species to what they were prior to human beings rapidly changing the planet.
Among land vertebrates species with an internal skeleton , species have been recorded going extinct since the year , or about 1. If this doesn't sound like much, it's important to remember extinction is always preceded by a loss in population abundance and shrinking distributions.
Based on the number of decreasing vertebrate species listed in the International Union for Conservation of Nature's Red List of Threatened Species , 32 percent of all known species across all ecosystems and groups are decreasing in abundance and range.
In fact, the Earth has lost about 60 percent of all vertebrate individuals since Australia has one of the worst recent extinction records of any continent, with more than species of vertebrates going extinct since the first people arrived over 50 thousand years ago.
And more than animal and 1, plant species are now considered threatened with imminent extinction. Although biologists are still debating how much the current extinction rate exceeds the background rate, even the most conservative estimates reveal an exceptionally rapid loss of biodiversity typical of a mass extinction event. In fact, some studies show that the interacting conditions experienced today, such as accelerated climate change , changing atmospheric composition caused by human industry, and abnormal ecological stresses arising from human consumption of resources, define a perfect storm for extinctions.
All these conditions together indicate that a sixth mass extinction is already well under way. This article is republished from The Conversation under a Creative Commons license. Read the original article.
If all species currently designated as critically endangered, endangered, or vulnerable go extinct in the next century, and if that rate of extinction continues without slowing down, we could approach the level of a mass extinction in as soon as to years. Climate change presents a long-term threat. By total volume, these past volcanoes emitted far more than humans do today; the Siberian Traps released more than 1, times the CO 2 than humans did in from burning fossil fuels for energy.
As mass extinctions show us, sudden climate change can be profoundly disruptive. Well before hitting that grim marker, the damage would throw the ecosystems we call home into chaos, jeopardizing species around the world—including us. All rights reserved.
Edaphosaurus A sail-backed edaphosaurus forages amid a Permian landscape in this artist's depiction. Fleeing Nothosaurs An artist's rendering shows hatchling nothosaurs heading for the safety of water as a hungry but terrestrial Ticinosuchus attacks near a lagoon in ancient Switzerland.
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Instead, massive eruptions in a hot spot at the center of what would eventually be the Atlantic Ocean created another bout of climate calamity. And it played like an echo of the End-Permian. How bad: About 80 percent of species and 47 percent of genera went extinct.
What died: This was not a good time to be a conodont. Already in decline, the last of these ribbonlike fish, as well as many reptiles, were among the hardest hit. What thrived: Dinosaurs really hit their stride after the End-Triassic, exploding in diversity, as did their archosaur relatives, the crocodylomorphs, descendants of which include modern crocodiles. When: Why: The cause of the End-Cretaceous extinction remains hotly debated. But researchers disagree on whether the asteroid strike caused or merely contributed to the die-off.
Whatever the catalyst, it appears a spike in carbon dioxide and a drop in ocean oxygen levels were followed by a rapid post-asteroid cooling. How bad: About 76 percent of species and 40 percent of genera went extinct.
What died: The sun finally set on the Long Day of the Dinosaur, though many other organisms were also wiped out, such as ammonites, mollusks with distinctive spiral shells. What thrived: Mammals quickly adapted to exploit newly vacated ecological niches, as did the sole surviving branch of dinosaurs, better known today as birds.
Across time and around the planet, extinctions of one or another individual species are always occurring. Determining extinction rates as they are unfolding is difficult, but a Science Advances study, using a range of conservative estimates, placed the current pace at up to times the normal background rate. Human activities are to blame, including population growth, increased resource consumption and climate change spurred by fossil fuel burning and the release of greenhouse gases.
The downward spiral begins with the destruction and fragmentation of habitat, and the introduction of invasive species and pathogens. The killing of individual members of a species through overhunting or poaching also takes its toll. Just ask any rhino, if you can find one. All of these activities can result, over time, in local extinctions known as extirpations. Even before global extinction of a species occurs, these extirpations reduce biodiversity and can destabilize ecosystems, leading to more extinctions.
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