Giant ground sloths may have been meat-eating scavengers

Modern sloths may be dedicated vegetarians, but at least one of their massive Ice Age cousins chowed down on meat when it had the chance. Darwin’s ground sloth — which could grow to over 3 meters long and weigh as much as about 2,000 kilograms — may have been an opportunistic scavenger, chemical analyses of fossil sloth hair suggest.

Paleontologist Julia Tejada of the University of Montpellier in France and colleagues analyzed the chemical makeup of two amino acids, the building blocks of proteins, within the fossil hair of two giant ground sloth species: Darwin’s ground sloth (Mylodon darwinii) of South America and the Shasta ground sloth (Nothrotheriops shastensis) of North America (SN: 4/25/18). The team compared these with samples from living sloths, anteaters and other modern omnivores.
Nitrogen isotopes, different forms of the element, can vary a lot among different food sources as well as between ecosystems. Those isotope values in one amino acid, glutamine, change significantly with diet, increasing the higher the animal is on the food chain. But diet has little impact on the nitrogen values in another amino acid, phenylalamine. By comparing the nitrogen isotopes in the two amino acids found in the sloths’ hair, the researchers were able to eliminate ecosystem effects and zoom in on diets.

The data reveal that while the diet of the Shasta ground slothwas exclusively plant-based, Darwin’s ground sloth was an omnivore, Tejada and colleagues report October 7 in Scientific Reports.

The findings upend what scientists thought they knew about the ancient animals. Scientists have assumed the ancient creatures were herbivores. That’s in part because all six modern species of sloth are confirmed vegetarians, and in part giant ground sloths’ teeth and jaws weren’t adapted for hunting or powerful chewing and tearing (SN: 6/20/16).

But Darwin’s ground sloth could have managed to ingest already-killed meat, Tejada and colleagues say. And that might help solve a long-standing puzzle: the apparent absence of large carnivorous mammals in South America at the time. Darwin’s ground sloth, the researchers add, may have filled a vacant ecological niche: the scavenger who wouldn’t say no to a meaty meal.

Lasers reveal construction inspired by ancient Mexican pyramids in Maya ruins

At Teotihuacan, near Mexico City, three giant pyramids rise above the ancient city’s main street, the Avenue of the Dead. The smallest of these is the Temple of the Feathered Serpent, which sits within La Ciudadela, or the Citadel, a massive sunken plaza with tall walls.

Now, more than a thousand kilometers away at the Maya capital of Tikal in what’s now Guatemala, researchers have found a smaller plaza and pyramid possibly modeled after La Ciudadela and its temple.

Teotihuacan is thought to have conquered Tikal in the year 378 (SN: 9/27/18). The finding adds to evidence of Teotihuacan’s influence over Tikal, the team reports September 28 in Antiquity.

“The architectural layout revealed by this study is stunning,” says anthropological archaeologist Nawa Sugiyama of the University of California, Riverside, who was not involved in the new research. “The very orthogonal city planning with specific orientation of the pyramids gives Teotihuacan a very characteristic architectural style, making it easy to identify any Teotihuacan influence abroad.”、
What’s more, the newfound structures had six construction phases, the researchers say, most dating to a time in Mesoamerica that archaeologists call the Early Classic period, which lasted from about 300 to 550. That means that the Tikal complex possibly predates the Teotihuacan conquest of the Maya city in 378. If true, that would add more evidence to an idea that scientists have worked on for decades — that these civilizations were in contact much earlier than the conquest of Tikal, possibly trading and making political connections with one another.

To uncover the pre-Columbian architecture, archaeologist Stephen Houston of Brown University in Providence, R.I., and colleagues at the Proyecto Arqueológico del Sur de Tikal along with the Pacunam LiDAR Initiative and the University of Texas at Austin used an airborne remote-sensing technique called lidar, or light detection and ranging.
“We knew this area in Guatemala was important to Teotihuacan culture,” says study coauthor David Stuart, director of the Mesoamerica Center of the University of Texas at Austin. But the place where the Citadel-inspired construction is located did not appear on old maps of the Tikal archaeological site because it is covered in vegetation. “As there was no visible stonework there, it was thought to be a natural hill,” Stuart says.

The team decided to look closer because the mound looked unusual for a Maya site. “Since the location was adjacent to an area in Tikal where many Teotihuacan-style artifacts were found in the 1980s, we thought it deserved more attention,” Stuart says. After reviewing the lidar mapping, Houston saw that the general plan of the buildings resembled the Ciudadela and its temple at Teotihuacan.

In her 2004 book The Ancient Maya: New Perspectives, Louisiana State University archaeologist Heather McKillop noted that the abundant presence of Teotihuacan-style architecture and pottery found in Tikal and a number of Maya sites across Guatemala is extensive evidence of the Teotihuacan influence across Mesoamerica from the year 400 to 700. The ancient city in Mexico thrived from about 100 to 750, but much about the people who lived there and why the city was destroyed and abandoned is still a mystery. The Aztecs gave the name Teotihuacanto the city centuries after its collapse.

“It is almost like Teotihuacan had installed their own neighborhood or embassy in Tikal,” says study coauthor and archaeologist Thomas Garrison, also at the University of Texas at Austin. Other research led by Sugiyama shows that “there was also a more permanent Maya presence in Teotihuacan before the conquest of Tikal as well, so influence probably went in both ways.”

Sugiyama studies the Plaza of the Columns Complex at Teotihuacan, where researchers have found Maya ceramics and evidence of Maya-style painted walls. “These murals were destroyed … before the 378 arrival event,” she says. “That makes us wonder whether the conquest [of Tikal] was one of the last chapters” in a long history of contact between the Mayas and the Teotihuacanos.

Eduardo Natalino dos Santos, a Mesoamerica historian at the University of São Paulo who did not take part in the study, agrees with Sugiyama. “The circulation of these ancient architectural styles show that the Mesoamerican Indigenous elites were connected. We used to see traces of one culture in a different region always as a result of a colonizing or domination process. Maybe this is not always the case,” he says.

New ideas on what makes a planet habitable could reshape the search for life

When considering where to look for extraterrestrial life, astronomers have mostly stuck with what’s familiar. The best candidates for habitable planets are considered the ones most like Earth: small, rocky, with breathable atmospheres and a clement amount of warmth from their stars.

But as more planets outside the solar system have been discovered, astronomers have debated the usefulness of this definition (SN: 10/4/19). Some planets in the so-called habitable zone, where temperatures are right for liquid water, are probably not good for life at all. Others outside that designated area might be perfectly comfortable.

Now, two studies propose revising the concept of “habitable zone” to account for more of the planets that astronomers may encounter in the cosmos. One new definition brings more planets into the habitable fold; the other nudges some out.

“Both papers focus on questioning the classical idea of the habitable zone,” says astronomer Noah Tuchow of Penn State University. “We should extend the range of places that we look, so we don’t miss habitable planets.”
Some overlooked planets could be much bigger than Earth, and potentially receive no starlight at all. Astrophysicist Nikku Madhusudhan of the University of Cambridge and colleagues propose a new category of possibly habitable planet that could be found at almost any distance from any kind of star.

These hypothetical planets have a global liquid-water ocean nestled under a thick hydrogen-rich atmosphere (SN: 5/4/20). Madhusudhan calls them “Hycean” planets, for “hydrogen” and “ocean.” They could be up to 2.6 times the size of Earth and up to 10 times as massive, Madhusudhan and colleagues report August 25 in the Astrophysical Journal. That thick atmosphere could keep temperatures right for liquid water even with minimal input from a star, while the ocean could protect anything living from crushing atmospheric pressure.

“We want to expand beyond our fixated paradigm so far on Earthlike planets,” Madhusudhan says. “Everything we’ve learned about exoplanets so far is extremely diverse. Why restrict ourselves when it comes to life?”

In the search for alien life, Hycean planets would have several advantages over rocky planets in the habitable zone, the team says. Though it’s difficult to tell which worlds definitely have oceans and hydrogen atmospheres, there are many more known exoplanets in the mass and temperature ranges of Hycean planets than there are Earthlike planets. So the odds are good, Madhusudhan says.

And because they are generally larger and have more extended atmospheres than rocky planets, Hycean planets are easier to probe for biosignatures, molecular signs of life. Detectable biosignatures on Hycean planets could include rare molecules associated with life on Earth like dimethyl sulfide and carbonyl sulfide. These tend to be too low in concentration to detect in thin Earthlike atmospheres, but thicker Hycean atmospheres would show them more readily.

Best of all, existing or planned telescopes could detect those molecules within a few years, if they’re there. Madhusudhan already has plans to use NASA’s James Webb Space Telescope, due to launch later this year, to observe the water-rich planet K2 18b (SN: 9/11/19).

That planet’s habitability was debated when it was reported in 2019. Madhusudhan says 20 hours of observations with JWST should solve the debate.

“Best-case scenario, we’ll detect life on K2 18b,” he says, though “I’m not holding my breath over it.”

Astronomer Laura Kreidberg of the Max Planck Institute for Astronomy in Heidelberg, Germany, thinks it probably won’t be that easy. Planets in the Hycean size range tend to have cloudy or hazy atmospheres, making biosignatures more difficult to pick up.

It’s also not clear if Hycean planets actually exist in nature. “It is a really fun idea,” she says. “But is it just a fun idea, or does it match up with reality? I think we absolutely don’t know yet.”

Rather than inventing a new way to bring exoplanets into the habitable family, Tuchow and fellow Penn State astronomer Jason Wright are kicking some apparently habitable planets out. The pair realized that the region of clement temperatures around a star changes as the star evolves and changes brightness.

Some planets are born in the habitable zone and stay there their entire lives. But some, possibly most, are born outside their star’s habitable zone and enter it later, as the star ages. In the August Research Notes of the American Astronomical Society, Tuchow and Wright suggest calling those worlds “belatedly habitable planets.”

When astronomers point their telescopes at a given star, the scientists are seeing only a snapshot of the star’s habitable zone, the pair say. “If you just look at a planet in the habitable zone in the present day, you have no idea how long it’s been there,” Tuchow says. It’s an open question whether planets that enter the habitable zone later in life can ever become habitable, he explains. If the planet started out too close to the star, it could have lost all its water to a greenhouse effect, like Venus did. Moving Venus to the position of Earth won’t give it its water back.

On the other end, a planet that was born farther from its star could be entirely covered in glaciers, which reflect sunlight. They may never melt, even when their stars brighten. Worse, their water could go straight from frozen to evaporated, a process known as sublimation. That scenario would leave the planet no time with even a cozy wet puddle for life to get started in.

These planets are “still in the habitable zone,” Tuchow says. “But it adds questions about whether or not being in the habitable zone actually means habitable.”

Scientists are racing to save the Last Ice Area, an Arctic Noah’s Ark

It started with polar bears.

In 2012, polar bear DNA revealed that the iconic species had faced extinction before, likely during a warm period 130,000 years ago, but had rebounded. For researchers, the discovery led to one burning question: Could polar bears make a comeback again?

Studies like this one have emboldened an ambitious plan to create a refuge where Arctic, ice-dependent species, from polar bears down to microbes, could hunker down and wait out climate change. For this, conservationists are pinning their hopes on a region in the Arctic dubbed the Last Ice Area — where ice that persists all summer long will survive the longest in a warming world.

Here, the Arctic will take its last stand. But how long the Last Ice Area will hold on to its summer sea ice remains unclear. A computer simulation released in September predicts that the Last Ice Area could retain its summer sea ice indefinitely if emissions from fossil fuels don’t warm the planet more than 2 degrees Celsius above preindustrial levels, which is the goal set by the 2015 Paris Climate Agreement (SN: 12/12/15). But a recent report by the United Nations found that the climate is set to warm 2.7 degrees Celsius by 2100 under current pledges to reduce emissions, spelling the end of the Arctic’s summer sea ice (SN: 10/26/21).

Nevertheless, some scientists are hoping that humankind will rally to curb emissions and implement technology to capture carbon and other greenhouse gases, which could reduce, or even reverse, the effects of climate change on sea ice. In the meantime, the Last Ice Area could buy ice-dependent species time in the race against extinction, acting as a sanctuary where they can survive climate change, and maybe one day, make their comeback.
Ecosystem of the frozen sea
The Last Ice Area is a vast floating landscape of solid ice extending from the northern coast of Greenland to Canada’s Banks Island in the west. This region, roughly the length of the West Coast of the United States, is home to the oldest and thickest ice in the Arctic, thanks to an archipelago of islands in Canada’s far north that prevents sea ice from drifting south and melting in the Atlantic.

As sea ice from others part of the Arctic rams into this natural barrier, it piles up, forming long towering ice ridges that run for kilometers across the frozen landscape. From above, the area appears desolate. “It’s a pretty quiet place,” says Robert Newton, an oceanographer at Columbia University and coauthor of the recent sea ice model, published September 2 in Earth’s Future. “A lot of the life is on the bottom of the ice.”

The muddy underbelly of icebergs is home to plankton and single-celled algae that evolved to grow directly on ice. These species form the backbone of an ecosystem that feeds everything from tiny crustaceans all the way up to beluga whales, ringed seals and polar bears.

These plankton and algae species can’t survive without ice. So as summer sea ice disappears across the Arctic, the foundation of this ecosystem is literally melting away. “Much of the habitat Arctic species depend on will become uninhabitable,” says Brandon Laforest, an Arctic expert at World Wildlife Fund Canada in Montreal. “There is nowhere else for these species to go. They’re literally being squeezed into the Last Ice Area.”
The last stronghold of summer ice provides an opportunity to create a floating sanctuary —an Arctic ark if you will — for the polar bears and many other species that depend on summer ice to survive. For over a decade, WWF Canada and a coalition of researchers and Indigenous communities have lobbied for the area to be protected from another threat: development by industries that may be interested in the region’s oil and mineral resources.

“The tragedy would be if we had an area where these animals could survive this bottleneck, but they don’t because it’s been developed commercially,” Newton says.

But for Laforest, protecting the Last Ice Area is not only a question of safeguarding arctic creatures. Sea ice is also an important tool in climate regulation, as the white surface reflects sunlight back into space, helping to cool the planet. In a vicious cycle, losing sea ice helps speed up warming, which in turn melts more ice.

And for the people who call the Arctic home, sea ice is crucial for food security, transportation and cultural survival, wrote Inuit Circumpolar Council Chair Okalik Eegeesiak in a 2017 article for the United Nations. “Our entire cultures and identity are based on free movement on land, sea ice and the Arctic Ocean,” Eegeesiak wrote. “Our highway is sea ice.”

The efforts of these groups have borne some fruit. In 2019, the Canadian government moved to set aside nearly a third of the Last Ice Area as protected spaces called marine preserves. Until 2024, all commercial activity within the boundaries of the preserves is forbidden, with provisions for Indigenous peoples. Conservationists are now asking these marine preserves to be put under permanent protection.

Rifts in the ice
However, there are some troubling signs that the sea ice in the region is already precarious. Most worrisome was the appearance in May 2020 of a Rhode Island—sized rift in the ice at the heart of the Last Ice Area. Kent Moore, a geophysicist at the University of Toronto, says that these unusual events may become more frequent as the ice thins. This suggests that the Last Ice Area may not be as resilient as we thought, he says.

This is something that worries Laforest. He and others are skeptical that reversing climate change and repopulating the Arctic with ice-dependent species will be possible. “I would love to live in a world where we eventually reverse warming and promote sea ice regeneration,” he says. “But stabilization seems like a daunting task on its own.”

Still, hope remains. “All the models show that if you were to bring temperatures back down, sea ice will revert to its historical pattern within several years,” says Newton.

To save the last sea ice — and the creatures that depend on it — removing greenhouse gases from the atmosphere will be essential, says oceanographer Stephanie Pfirman of Arizona State University in Tempe, who coauthored the study on sea ice with Newton. Technology to capture carbon, and prevent more carbon from entering the atmosphere, already exists. The largest carbon capture plant is in Iceland, but projects like that one have yet to be implemented on a major scale.

Without such intervention, the Arctic is set to lose the last of its summer ice before the end of the century. It would mean the end of life on the ice. But Pfirman, who suggested making the Last Ice Area a World Heritage Site in 2008, says that humankind has undergone big economic and social changes — like the kind needed to reduce emissions and prevent warming — in the past. “I was in Germany when the [Berlin] wall came down, and people hadn’t expected that to happen,” she says.

Protecting the Last Ice Area is about buying time to protect sea ice and species, says Pfirman. The longer we can hold on to summer sea ice, she says, the better chance we have at bringing arctic species —from plankton to polar bears — back from the brink.

What the Perseverance rover’s quiet landing reveals about meteor strikes on Mars

The lander was listening. On February 18, NASA’s InSight lander on Mars turned its attention to the landing site for another mission, Perseverance, hoping to detect its arrival on the planet.

But InSight heard nothing.

Tungsten blocks ejected by Perseverance during entry landed hard enough to create craters on the Martian surface. Collisions like these — whether from space missions or meteor strikes — send shock waves through the ground. Yet in the first experiment of its kind on another world, InSight failed to pick up any seismic waves from the blocks’ impacts, researchers report October 28 in Nature Communications.

As a result, researchers think that less than 3 percent of the energy from the impacts made its way into the Martian surface. The intensity of impact-generated rumblings varies from planet to planet and is “really important for understanding how the ground will change from a big impact event,” says Ben Fernando, a geophysicist at the University of Oxford.
But getting these measurements is tricky. Scientists need sensitive instruments placed relatively near an impact site. Knowing when and where a meteor will strike is nearly impossible, especially on another world.

Enter Perseverance: a hurtling space object set to hit Mars at an exact time and place (SN: 2/17/21). To help with its entry, Perseverance dropped about 78 kilograms of tungsten as the rover landed about 3,450 kilometers from InSight. The timing and weight of the drop provided a “once-in-a-mission opportunity” to study the immediate seismic effects of an impact from space, Fernando says.

The team had no idea whether InSight would be able to detect the blocks’ impacts or not, but the quiet arrival speaks volumes. “It lets us put an upper limit on how much energy from the tungsten blocks turned into seismic energy,” Fernando says. “We’ve never been able to get that number for Mars before.”