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June 20, 2018

Easter Island's Demise May Have Surprising New Explanation

The downfall of Easter Island may have had more to do with preexisting environmental conditions than degradation by humans, according to a new study of the remote speck of land made famous by its enormous stone-head statues.

Easter Island, also known as Rapa Nui, was first settled around A.D. 1200, and Europeans landed on its shores in 1722. The circumstances surrounding the collapse of the indigenous population of Rapa Nui are hotly debated both in academia and popular culture. Scientist and author Jared Diamond argued in his 2005 book “Collapse: How Societies Choose to Fail or Succeed” (Viking Press) that prior to European contact, the indigenous people of the island degraded the environment to the extent that they could no longer thrive.

The new study suggests that Easter Island’s people were, indeed, suffering before Europeans came along. The story of their downfall, however, may be less about environmental degradation than the pre-existing environmental constraints of the 63-square-mile (163 square kilometers) isle. [Image Gallery: The Walking Statues of Easter Island]

“The results of our research were really quite surprising to me,” said study co-author Thegn Ladefoged, an anthropologist at the University of Auckland in New Zealand. “Indeed, in the past, we’ve published articles about how there was little evidence for pre-European-contact societal collapse.” 

Collapse of civilization?

The new study challenged Ladefoged and his colleagues’ view. Changes on Easter Island have been well documented, archaeologically. Over time, elite dwellings were destroyed, inland agricultural fields were abandoned, and people took refuge in caves and began manufacturing more and more spear points made out of volcanic glass called obsidian, perhaps suggesting a period of war and upheaval. 

The problem with pinning down the island’s history, according to the researchers, is that the dates of all these events and abandonments remain murky. Going into the study, the researchers expected to find that most of the disaster occurred after Europeans arrived, Ladefoged told Live Science.

To clarify the timeline, the researchers analyzed more than 400 obsidian tools and chipped-off obsidian flakes from six sites scattered around the island, focusing in particular on three with good information on climate and soil chemistry.

Obsidian absorbs water when exposed to air. By measuring the amount of water absorption in the surfaces of the obsidian tools and flakes, the research team was able to gauge how long those surfaces have been exposed, thus revealing when the tools were made. A greater number of tools from a certain time period indicates heavier human use of that area during that time. [History’s 10 Most Overlooked Mysteries]

Natural challenges

The obsidian dates varied widely across the sites. Site 1, on the northwestern coast of the island, saw a steady increase in use between about 1220 and 1650, with a fast decline starting after 1650 — long before Europeans arrived on the island.

Site 2, an interior mountainside site, saw a rapid increase in land use between about 1200 and 1300, a slower increase until about 1480, and then constant use until a decline that started between 1705 and 1710, also before European contact. By the time Europeans came along, coastal Site 1 was at about 54 percent of its peak land use, and mountainous Site 2 was at only about 60 percent.

Site 3 told a different story. This near-coastal area saw a slow increase in human activity between 1250 and 1500, and then a faster increase until about 1690, after which settlement remained fairly constant until after European contact. In fact, the decline in use of this site didn’t begin until 1850 or later, the researchers found.

The differing climates of the sites may explain the uneven decline, the researchers said. Site 1 is in the rain shadow of the volcano Ma’unga Terevaka, making it prone to droughts. Site 2 is wetter, but its soil fertility is low. Site 3, the longest-lasting spot, is both rainy and fertile.

What this means is that the people of Easter Island may have been struggling against natural environmental barriers to success, rather than degrading the environment themselves, the researchers reported Monday (Jan. 5) in the journal Proceedings of the National Academy of Sciences.

“It is clear that people were reacting to regional environmental variation on the island before they were devastated by the introduction of European diseases and other historic processes,” Ladefoged said. The next step, he said, would be to take a detailed look at the archaeological remnants of dwellings on the island over time to better understand how humans and the environment interacted.

Follow Stephanie Pappas on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Copyright 2015 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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Easter Island's Demise May Have Surprising New Explanation

Greenland's Ice-Melt Models May Be Too Sunny

The vast ice sheet covering Greenland could melt more quickly in the future than existing models predict, new research suggests.

Scientists looked at satellite data collected by NASA’s ICESat spacecraft and Operation IceBridge and plotted the elevation of 100,000 sites on Greenland from 1993 to 2012.

The researchers were able to create new, more precise estimates for how much ice had melted in the past. They also found that the ice melts in a rather complex pattern, which should be of interest to scientists trying to predict how much ice will disappear in the future. [Images: Greenland’s Gorgeous Glaciers]

More than a mile thick in most areas, the Greenland Ice Sheet covers nearly all of interior Greenland, an Arctic island about three times the size of Texas. If the entire ice sheet melted, sea levels around the world would rise about 20 feet (6 meters), according to the National Snow and Ice Data Center.

Though such a catastrophic scenario isn’t likely to happen anytime soon, smaller increases in sea level could still boost the power of coastal storms, threaten to flood major cities and displace millions of people. During the 20th century, sea levels rose by about 6.7 inches (17 centimeters). According to the latest report from the Intergovernmental Panel on Climate Change (IPCC), the current scientific consensus is that sea levels could creep up by 11 inches to 38 inches (28 to 98 cm) by 2100, in part because of melting in the Greenland and Antarctic ice sheets. 

The new research found that an average of 243 gigatons (or 66.5 cubic miles) of the Greenland Ice Sheet melted each year from 2003 to 2009. (The scientists had the most comprehensive data for this period.) That’s enough meltwater to raise oceans by about 0.027 inches (0.68 millimeters) per year, the researchers said.

The study didn’t make any exact predictions for how much of Greenland’s ice may melt in the future, but the authors think that current models underestimate the extent of the problem.  

“My personal opinion is that most of the predictions of this as far as Greenland is concerned are too low,” study author Beata Csatho, an associate professor of geology at the University at Buffalo, said in a video statement.

Existing models for predicting changes in ice-sheet melt and sea-level rise are typically extrapolated from data on just four of Greenland’s 242 glaciers: Jakobshavn, Helheim, Kangerlussuaq and Petermann. That’s a problem, according to the study’s authors, because glaciers — even ones right next to each other — can behave quite differently in any given year. Today’s models also tend to ignore southeast Greenland’s ice cover, which is experiencing heavy losses, the researchers found. In 2005, melting in this region accounted for more than half of the losses to the Greenland Ice Sheet.

Csatho and her colleagues say it’s not easy to predict how glaciers will respond to global warming, because they don’t always melt as the temperature rises. Their data showed that sometimes the glaciers covering Greenland thickened when the temperature rose, while some areas both thinned and thickened, with abrupt reversals.

To help other researchers create better prediction models, the scientists put all of Greenland’s glaciers into seven groups, based on the characteristics of their melting behavior from 2003 to 2009.

“Understanding the groupings will help us pick out examples of glaciers that are representative of the whole,” Csatho said in a statement. “We can then use data from these representative glaciers in models to provide a more complete picture of what is happening.”

The findings were published Monday (Dec. 15) in the journal Proceedings of the National Academy of Sciences.

Follow Megan Gannon on Twitter. Follow us @livescienceFacebook Google+. Original article on Live Science.

Copyright 2014 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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Greenland's Ice-Melt Models May Be Too Sunny

European Probe Survived Comet Landing with Luck and Great Design

Europe’s Rosetta mission pulled off the first-ever soft landing on a comet Wednesday thanks to a lot of great engineering and hard work — along with a healthy dose of luck, mission scientists say.

Rosetta’s Philae lander successfully touched down on Comet 67P/Churyumov-Gerasimenko early Wednesday morning (Nov. 12), more than 300 million miles (483 million kilometers) from Earth. But Philae’s anchoring harpoons didn’t fire as planned, and the 220-lb. (100 kilograms) probe bounced off the comet twice before settling onto its icy surface for good.

Philae survived the dramatic landing intact, however, and is already gathering a variety of data about the 2.5-mile-wide (4 km) Comet 67P. [Rosetta Comet Landing: Complete Coverage]

“We were very, very lucky yesterday — so much luck,” Stephan Ulamec, Philae lander manager at the DLR German Aerospace Center, said during a news conference Thursday. 

Bouncing off a comet

Philae’s first bounce off 67P was a big one, sending the lander about 0.6 miles (1 kilometer) above the comet’s surface, Ulamec said. Philae eventually came down again 1 hour and 50 minutes later, likely about 0.6 miles away from the original landing site. (The team still isn’t sure exactly where the lander ended up.)

But the probe was nearly lost to space. It rebounded off 67P’s surface at 0.85 mph (1.37 km/h); with a bounce of about 1 mph (1 km/h), Philae would have escaped the comet’s minuscule gravity altogether, said Peter Schultz, a geoscientist at Brown University in Rhode Island. (Schultz has worked on three different NASA missions to comets and asteroids but is not part of the Rosetta team.)

To put those numbers in perspective: The escape velocity at Earth’s surface is about 25,000 mph (40,230 km/h).

The second bounce lasted just 7 minutes and featured a rebound speed of 0.067 mph (0.11 km/h), Ulamec said. When it was over, Philae was oriented nearly vertically on the comet’s surface, with one of its three landing legs apparently dangling into empty space. But the probe came through its ordeal in good shape and ready to collect data, which surprised Schultz. [Best Close Encounters of the Comet Kind]

“I’m actually flabbergasted,” he told Space.com. “Somehow, the German gods were looking [over the mission].”

Good engineering certainly helped as well. As Philae spiraled down toward the comet, it did have enough kinetic energy to escape back into space, said Mark Hofstadter, deputy principal investigator for MIRO (Microwave Instrument on the Rosetta Orbiter). However, shock absorbers in Philae’s legs absorbed and converted to heat much of that energy when the probe hit the surface the first time, he noted.

“Plus, a little energy was absorbed by the surface the lander hit (maybe crushing some rocks),” Hofstadter, who’s based at NASA’s Jet Propulsion Laboratory in Pasadena, California, told Space.com via email. “So knowing that even a tiny amount of energy was dissipated means that the lander would not have enough energy to escape again.”

Indeed, the Philae team built some redundancy into the lander, allowing it to cope with a variety of different situations and parameters on Comet 67P, Ulamec said.

“The harpoons did not work, but the landing gear worked very nicely,” he said.

And Schultz was quick to praise the Rosetta team and its multiple accomplishments. (This past August, the Rosetta mothership caught 67P after a 10-year chase and became the first spacecraft ever to enter orbit around a comet.)

Schultz observed that the Rosetta mission was conceived and developed more than 20 years ago, when researchers knew far less about comets than they do today.

“It’s remarkable that this has worked so well,” he said. “And this is why it’s always worth it to dare, and to explore. That’s the big lesson for me.”

Lots of science to come

With the probe in its current precarious position, the mission team is hesistant to try firing the anchoring harpoons again or use Philae’s drilling instrument, which can collect samples from more than 8 inches (20 centimeters) beneath the comet’s surface, Ulamec said.

But Philae is already well into its “first science sequence” phase, or FSS, using its 10 different instruments to get a first taste of the comet. The FSS will last until Philae’s primary batteries run out — perhaps two to three days after touchdown, mission officials have said.

The plan also calls for Philae to keep studying Comet 67P over the long term, using batteries that will be recharged by solar cells aboard the lander. This second phase was envisioned to last a maximum of three months or so, but expectations may have to be recalibrated downward after the double-bounce landing; Philae is only getting about 1.5 hours of sunlight per day in its current location, while the intended landing site offered 6 to 7 hours per day, the lander’s handlers say.

Regardless, Philae should still manage to collect a great deal of interesting data, mission team members say. The lander’s scientific gear is designed to study the composition and structure of Comet 67P in great detail. For example, one instrument employs radio waves to probe the interior of the comet’s nucleus, while another identifies complex organic molecules on the surface.

“This is real comet geology now,” Schultz said. “I think it’s going to be a spectacular mission.”

Comets are icy remnants left over from the solar system’s formation 4.6 billion years ago, so observations made by Philae and the Rosetta mothership should shed light on the conditions prevalent when Earth and the other planets were taking shape, mission officials have said.

The Rosetta orbiter will continue studying Comet 67P through at least December 2015, observing how the comet changes as it gets closer and closer to the sun. (67P’s closest approach will come in August 2015, when it zooms within 1.25 Earth-sun distances of our star.)

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

Copyright 2014 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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European Probe Survived Comet Landing with Luck and Great Design