Welcome to the sixth mass extinction (and yes, it’s our fault)

A weekly roundup of the best in science journalism, doodled.

June 25, 2015

We might be going the way of the dinosaur if we don’t get our acts together.

Studies suggesting that the planet is in the middle of a sixth mass-extinction event have gotten a lot of flak lately. So a group of scientists from Stanford, the University of California at Berkeley, Princeton, the National Autonomous University of Mexico, and the University of Florida all got together to determine whether the findings in question were, in fact, overblown—and alas, they weren’t. The group of researchers found that the rate of extinction for the last 115 years was 50 times what it would have been under normal conditions (basically, without us humans around).

Based on conservative estimates for “background extinction”—the number of vertebrate extinctions that would naturally occur over a given period of time—the scientists found that a total of about nine species should have gone extinct since 1900. In reality, 477 vertebrates are believed to have blinked out of existence, and 198 are confirmed extinct. If we just consider the demise of those 198, the current extinction rate is 22 times higher than it should be. That ain’t right.

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Bright-red crab bodies are carpeting SoCal beaches.

Photo: Tim Buss/Flickr

Photos like this one, showing hundreds of thousands of dead tuna crabs washed up on beaches in Southern California, have been upsetting me this week. These cute and delicate natives of Baja are carried to and fro on ocean currents most of their adult lives. The problem with that free and easy lifestyle is that when the water gets hot, the crabs get going—only in this case, they’ve gone and gotten themselves washed up on beaches farther north than they usually venture. 

Scientists aren’t sure exactly what’s happening but think the die-off could be a result of warmer water currents related to El Niño. Tuna crabs have been known to wash ashore when they spawn in great numbers but never to this degree. The Pacific Ocean, from California to northern Washington, also has a toxic algal bloom problem right now, and that, too, could be killing the crabs. If that’s the case, scientists are warning against eating the tuna crabs in case their meat contains toxins. 

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The beauty of symmetry, jellyfish style.

Image courtesy of Michael Abrams, Ty Basinger, and Christopher Frick, California Institute of Technology

Mike Abrams, a grad student at CalTech, had meant to study jellyfish immortality. These freaky-deaky invertebrates can revert to their younger polyp forms when they need to, essentially living indefinitely. Abrams’ samples, however, were late to arrive. So he ordered some juvenile moon jellies to mess with in the meantime and, like any normal scholar, started amputating their limbs (don’t worry, they were under anesthesia).

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What happened next was unexpected—and never before seen by scientists. When you cut off one of these jellies’ arms, they can change the location of their other arms (they have eight) to re-achieve symmetry, all by just pumping their muscles as they would for normal movement. About 72 percent to 96 percent of the moon jellies he studied could do this—and they then went on to lead perfectly normal and productive adult lives, albeit with fewer tentacles.

 

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We’re slurping up groundwater quickly, and we don’t know how much is left.

Matt's GIFs/Tumblr

We’re taking so much water from the ground that aquifers can’t recharge quickly enough to meet our demand. Two recent papers from scientists at the University of California, Irvine show that one-third of the globe’s aquifers are overstressed. NASA’s Grace satellites assess groundwater levels from space by detecting changes in the gravitational pull of water over time. Scientists can then use that data to determine which aquifers are running low the fastest. The amount of groundwater that actually remains, however, is unknown, so the authors are calling for a coordinated global effort to research the problem more closely before, well, chaos ensues.

The aquifers in the worst shape are in various shades of red on the NASA map below. The ones concerning scientists the most are those found in locations where people rely on them heavily—and where a combination of population growth and social unrest could create a humanitarian disaster. The Arabian aquifer system, for example, provides water to 60 million people. Other aquifers in dire need of replenishment are in northwestern India and Pakistan, northern Africa, Russia’s Caucasus region, and California’s Central Valley.

Groundwater depletion has huge ecological impacts, too. Land subsides and rivers run dry, leaving fish and other wildlife with nowhere to go and nothing to drink. 

Illustrated by UC Irvine/NASA/JPL-Caltech

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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