Dome effect dōm ih-fekt n.
Airborne black carbon, also called soot, can cause the dome effect by warming the atmosphere’s top layer and blocking sunlight that would otherwise warm the surface air. The reduced temperature difference between the two layers lowers the boundary between them. This effect traps pollution around major cities, worsening air quality, new research suggests.

Researchers observed the dome effect around several of China’s megacities in December 2013. The compressed near-surface layer of the atmosphere led to thick hazes of pollution, the researchers report online March 16 in Geophysical Research Letters. Reducing local black carbon emissions from industry, biofuel burning, diesel vehicles and coal burning would quickly improve air quality around many megacities, the researchers propose.

The sperm whale is one of the odder-looking cetaceans swimming the oceans. Its massive, blocky head is unlike anything sported by other whales. The space above the mouth holds two large, oil-filled organs stacked one on top of the other — the spermaceti organ on top, and another below it called the (we did not make this up) junk. And in the last couple of decades, scientists have determined that the two organs amplify and direct the sonar clicks that the whales use to navigate in the water.

But there have long been suggestions that the massive head could serve another purpose — to ram other whales. The hypothesis dates back to the 19th century, when sperm whales sometimes rammed — and even sank — whaling vessels. “The structure and strength of the whale’s head is admirably designed for this mode of attack,” wrote Owen Chase, first mate of the Essex, which was sank by a whale and inspired the tale of Moby Dick.

Scientists have largely been leery of this hypothesis, though, in part because ramming would risk damage to organs used to generate sound, and because no one had seen a sperm whale ram another. Or at least no one had ever reported such an event in the scientific literature. But a new study, appearing April 5 in PeerJ, shows that Owen and his whaling buddies just may have been right.

Olga Panagiotopoulou of the University of Queensland in Australia and colleagues created computer simulations of a sperm whale’s head and what might happen when the head rammed another object. Partitions of connective tissue inside the junk, they found, appear to reduce the stresses created by impact, “and thus potentially function as a protective mechanism during ramming,” the team writes.

An impact creates tension in the connective tissue that serves as partitions between pockets of oil in the junk. That tension disperses the impact over a greater volume of the head, protecting both bone and soft tissue from injury. When the connective tissue was removed from the simulations, stresses increased by 45 percent and it became more likely that the skull would crack.

Scars on the heads of sperm whales tend to be around the junk, which may indicate that the whales avoid contact over the spermaceti organ — behind which is the whale’s sound generating system, the researchers note. So if the whales are ramming into one another, they probably can do so without hurting their ability to generate sonar clicks.

But are sperm whales really ramming each other? There is other evidence to suggest they just might be. For one, male sperm whales are as much as three times bigger than females, and such size differences are often found in species in which males compete through fighting. There are those sunken whaling ships, too, which add to the argument that ramming behavior may have been something natural for the whales.
But there’s also a report from a wildlife pilot who, on January 30, 1997, while flying over the Gulf of California, saw two males swim directly toward each other at a speed of about 17 kilometers per hour — and then collide, forehead to forehead.

Just before impact, the whales dove just below the surface of the water. That may explain why no one else has reported such sperm whale contests: If they’re occurring below the water’s surface, a person would have to be directly above the event, or in the water with the whales. And besides, if two 50-ton mammals are about to go head-to-head, it might be best to get out of the way.

The U.S. Environmental Protection Agency, criticized for understating how much methane the United States spews into the atmosphere, has boosted its estimate of total U.S. methane emissions by 13 percent. That’s an increase of more than 3.4 million metric tons of the greenhouse gas and has the same long-term global warming impact as a year’s worth of emissions from about 20 million cars.

The new calculation, released in an EPA report April 15, revises the agency’s U.S. methane emission estimates for 2013 to 28.859 million metric tons, up from the agency’s previous estimate of 25.453 million metric tons. Two-thirds of that increase comes from the natural gas and petroleum sectors, with much of the rest coming from landfills. The report also provides the first estimate of methane emissions for 2014, a slight increase to 29.233 million metric tons.
Globally, methane emissions account for about a quarter of human-caused global warming. Several studies over the last few years have suggested that EPA significantly underestimated the U.S. share of those emissions (SN Online: 4/14/16).

While the new methane estimates are “a step in the right direction,” the agency still has a ways to go, says David Lyon, an environmental scientist at the Environmental Defense Fund. Even with the higher methane estimates, the agency is still undercounting U.S. emissions by about 20 to 60 percent, Lyon says. EPA’s reporting influences U.S. regulation of methane-producing industries such as agriculture and fossil fuel production.

A sizable portion of the still-at-large methane probably comes from “super emitters,” methane sources that contribute a disproportionate share of total emissions. These sources are typically malfunctioning equipment, making them difficult for EPA to account for.

A century and a half ago, a young paleontologist named Othniel Charles Marsh persuaded his uncle, philanthropist George Peabody, to give Yale University $150,000 for a museum of natural history. And so Yale’s Peabody Museum was born, an institution that has repeatedly upended how people understand Earth’s past. In House of Lost Worlds, Richard Conniff tells the story of the Peabody through the curious characters connected to it.
Marsh is arguably the best known, for his fossil-collecting rivalry with Edward Drinker Cope (the infamous Bone Wars) and as the discoverer (or describer) of Stegosaurus, Brontosaurus, Triceratops and Allosaurus, to name a few. Other characters include James Dwight Dana, who Conniff calls “the Linnaeus of the geological world”; G. Evelyn Hutchinson, the father of modern ecology; and Hiram Bingham III, who brought Machu Picchu to public attention in the 1910s (and is thought, by some, to have been the inspiration for Indiana Jones). The book is celebration, not exposé, but Conniff still conveys the researchers’ full personalities, including their competitive natures, along with academic squabbling.

Squeezed in throughout is the story of the building itself — perpetually undersized and often underappreciated — yet, as Conniff seems to remind us, the place where the soul of the science resides. As Hutchinson said, the museum “began to play a great part in my life as soon as I stepped into it.”

Conniff doesn’t go so far as to suggest that the museum makes the man (and, through no fault of Conniff’s, most of the leading characters are men). But he views the Peabody as a rich repository of knowledge. Its walls enclose over 150 years of insights built on discoveries built on insights, ad infinitum. Without the artifacts brought back from Machu Picchu (later returned to Peru after a bitter battle), anthropologists wouldn’t have redefined the site as an estate for Incan emperors. It was Marsh’s studies of dinosaurs, and horses, that positioned the Peabody to teach evolution when others were attacking it. And the first reconstruction of a feathered dinosaur’s colors (SN: 2/27/10, p. 9) depended on a fossilized squid left mostly unnoticed in the Peabody for over a century.

Throughout the book, Conniff emphasizes the discoveries yet to be made and the pleasure of finding out something new. “Please,” he invites readers, “step inside.”

Raging wildfires could burn away efforts to reduce Arctic-damaging soot emissions. Soot produced by burning fossil fuels and plants, also called black carbon, can cause respiratory diseases and greenhouse warming, and can accelerate the melting of ice.

Rising temperatures and changing weather patterns will shift where and how fiercely wildfires burn and spew soot, new simulations show. Outside of the tropics, fire seasons will last on average one to three months longer during the 2090s than they do currently, researchers report online April 8 in the Journal of Geophysical Research: Atmospheres. Soot emissions from wildfires will as much as double in regions that border the Arctic and counteract projected reductions in soot from human activities, the researchers predict.
“Humankind would do well to proactively develop adequate land and fire management strategies to have at least some control on future wildfire emissions,” says study coauthor Andreas Veira, an earth system scientist at the Max Planck Institute for Meteorology in Hamburg.

Predicting the future of fires is difficult because many factors — from weather to vegetation — influence wildfires. Veira and colleagues strung together three different computer simulations that projected the impact of climate change on wildfires (SN Online: 7/15/15). The first predicted future changes in global vegetation, which fed into the second, a wildfire simulation called SPITFIRE. Finally, the researchers plugged their predicted fires into a climate simulation.

If carbon emissions aren’t cut, overall soot emissions from wildfires will stay fairly steady but shift in location. Outside of the tropics, wildfire soot emissions will increase 49 percent by the end of the century as fire seasons get longer, the researchers predict. In the tropics, changing land usage and fewer human-caused ignitions due to urbanization will help decrease emissions there by 37 percent.

A northward shift in wildfires will push more soot emissions toward the Arctic, the researchers warn. Fallen soot darkens ice and snow, accelerating melting (SN: 10/5/13, p. 26). A 2009 study estimated that soot was responsible for more than a third of Arctic warming between 1976 and 2007. The new simulations show that about 53 percent more soot will fall on the Arctic at the end of the century, even if humans cut their own soot emissions in half.

Many factors that could influence future wildfires remain uncertain, says atmospheric scientist Shane Murphy of the University of Wyoming in Laramie. “We shouldn’t take the absolute numbers to mean too much, just to inform us that there’s the potential for severe consequences.”

A year ago, researchers in two small submarines were exploring a seamount — an underwater, flat-topped mountain — off the Pacific coast of Panama when they noticed a dense cloud of sediment extending 4 to 10 meters above the seafloor. One of the submarines approached closer, and the scientists could soon see what was kicking up the cloud: thousands of small, red crabs that were swarming together like insects.

“The encounter was unexpected and mesmerizing,” Jesús Pineda of the Woods Hole Oceanographic Institution in Massachusetts and colleagues write in a paper published April 12 in Peer J.

The team decided to investigate further. They sent an autonomous underwater vehicle to pass over the swarm several times, capturing images and video of the crabs. At the densest points in the swarm, there were more than 70 crabs in a square meter of ocean bottom, and this occurred consistently in a water depth of 350 to 390 meters. The crabs, all 2.3 centimeters in carapace length and larger, were moving together in the same general direction. Some would jump and swim for about 10 centimeters or so before landing back in the pack.
Using one of the submarines, the researchers collected some crabs from the swarm. Back in the lab in Woods Hole, they used DNA barcoding to identify the species: Pleuroncodes planipes. This is the same species of crab that has sometimes washed up in mass stranding events on California beaches, which the team confirmed by comparing the DNA barcodes to those of crabs from a stranding event in La Jolla, Calif., in June 2015.

For reasons that scientists still don’t fully understand, seamounts are ecological hot spots where plankton get trapped and feed a wide array of fish and marine mammals higher up in the food web. Fishermen have figured out that they can take advantage of this, but scientists are just now getting into the game and exploring these sites. Because of this, less than one percent of the world’s seamounts have been checked out by researchers. That probably explains why no one had seen a crab swarm like this before on a seamount.
But this is not the first time crabs have been seen swarming. Scientists have previously documented large aggregations of king crabs, spider crabs, tanner crabs and lyre crabs on the seafloor. Such behavior may be linked to reproduction.

And then there are the red crabs of Christmas Island in the Indian Ocean, which swarm in the millions during the wet season, coming out of the forests and making a long trek to the beach for a massive mating party.

In a 1967 episode of Star Trek, Captain Kirk and crew investigated the mysterious murders of miners on the planet Janus VI. The killer, it turned out, was a rock monster called the Horta. But the Enterprise’s sensors hadn’t registered any signs of life in the creature. The Horta was a silicon-based life-form, rather than carbon-based like living things on Earth.

Still, it didn’t take long to determine that the Horta was alive. The first clue was that it skittered about. Spock closed the case with a mind meld, learning that the creature was the last of its kind, protecting its throng of eggs.
But recognizing life on different worlds isn’t likely to be this simple, especially if the recipe for life elsewhere doesn’t use familiar ingredients. There may even be things alive on Earth that have been overlooked because they don’t fit standard definitions of life, some scientists suspect. Astrobiologists need some ground rules — with some built-in wiggle room — for when they can confidently declare, “It’s alive!”
Among the researchers working out those rules is theoretical physicist Christoph Adami, who watches his own version of silicon-based life grow inside a computer at Michigan State University in East Lansing.
“It’s easy when it’s easy,” Adami says. “If you find something walking around and waving at you, it won’t be that hard to figure out that you’ve found life.” But chances are, the first aliens that humans encounter won’t be little green men. They will probably be tiny microbes of one color or another — or perhaps no color at all.

By definition
Trying to figure out how to recognize those alien microbes, especially if they are very strange, has led scientists to propose some basic criteria for distinguishing living from nonliving things. Many researchers insist that features such as active metabolism, reproduction and Darwinian evolution are de rigueur for any life, including extraterrestrials. Others add the requirement that life must have cells big enough to contain protein-building machines called ribosomes.

But such definitions can be overly restrictive. A list of specific criteria for life may give scientists tunnel vision, blinding them to the diversity of living things in the universe, especially in extreme environments, says philosopher of science Carol Cleland of the University of Colorado Boulder. Narrow definitions will “act as blinkers if you run into a form of life that’s very different.”

Some scientists, for instance, say viruses aren’t alive because they rely on their host cells to reproduce. But Adami disagrees. “There’s no doubt in my mind that biochemical viruses are alive,” he says. “They don’t carry with them everything they need to survive, but neither do we.” What’s important, Adami says, is that viruses transmit genetic information from one generation to another. Life, he says, is information that replicates.
Darwinian evolution should be off the table, too, Cleland says. Humans probably won’t be able to tell at a quick glance whether something is evolving, anyway. “Evolvability is hard to detect,” she says, “because you’ve got a snapshot and you don’t have time to hang around and watch it evolve.”

Cell size restrictions may also squeeze minuscule microbes out of consideration as aliens. But a cell too tiny to contain ribosomes may still be big enough if it uses RNA instead of proteins to carry out biochemical reactions, says Steven Benner, an astrobiologist at the Foundation for Applied Molecular Evolution in Alachua, Fla. Cells are thought necessary because they separate one organism from another. But layers of clay could provide the needed separation, Adami suggests. Cleland postulates that life could even exist as networks of chemical reactions that don’t require separation at all.

Such fantastical thinking can loosen the grip of rigid criteria limiting scientists’ ability to recognize alien life when they see it. But they will still need to figure out where to look.
Up close and personal
With the discovery in recent years of more than a thousand exoplanets far beyond the solar system, the odds favoring the existence of extraterrestrial life in the cosmos are better than ever. But even the most powerful telescopes can’t detect microscopic organisms directly. Chances of finding microbial life are much higher if scientists can reach out and touch it, which means looking within our solar system, says mineralogist Robert Hazen, of the Carnegie Institution for Science in Washington, D.C.

“You really need a rover down on its hands and knees analyzing chemicals,” Hazen says. Rovers are sampling rocks on Mars (SN: 5/2/15, p. 24) and the Cassini probe has bathed in geysers spewing from Saturn’s icy moon Enceladus (SN: 10/17/15, p. 8). Those mechanical explorers and others in the works may send back signs of life.

But those signs are probably going to be subtle, indirect “biomarkers.” It may be surprisingly difficult to tell whether those biomarkers are from animals, vegetables, microbes or minerals, especially at a distance.

“We really need to have life be as obvious as possible,” says astrobiologist Victoria Meadows, who heads the NASA Astrobiology Institute’s Virtual Planetary Laboratory at the University of Washington in Seattle. By obvious, she partly means Earth-like and partly means that no chemical or geologic process could have produced a similar signature.
Some scientists say life is an “I’ll know it when I see it” phenomenon, says Kathie Thomas-Keprta, a planetary geologist. But life may also be in the eye of the beholder, as Thomas-Keprta knows all too well from studying a Martian meteorite. She was part of a team at the NASA Johnson Space Center in Houston that studied a meteorite designated ALH84001 (discovered in Antarctica’s Allan Hills ice field in 1984).

In 1996, a team led by Thomas-Keprta’s late colleague David McKay claimed that carbonate globules embedded in the meteorite resembled microscopic life on Earth. The researchers found large organic molecules with the carbonate, indicating that they formed at the same time. Thomas-Keprta also identified tiny magnetite crystals overlapping the globules that closely resemble crystals formed by “magnetotactic” bacteria on Earth. Such bacteria use chains of the crystals as a compass to guide them as they swim in search of nutrients. The researchers believed that they were looking at fossils of ancient Martians.

Other researchers disagreed. The globules and crystals could have formed by chemical or geologic processes, not biology, critics said. Since then, the claim of fossilized Martian life has been widely dismissed.

Surely, recognizing something that is still alive, rather than dead and turned to rock, would be much simpler. But don’t bet on it, Cleland says. There may even be strange forms of life on Earth — a shadow biosphere — that people have overlooked.

Desert varnish
One bit of evidence for shadow terrestrials is “desert varnish,” the dark stains on the sunny sides of rocks in arid areas. Odd, communal life-forms could be sucking energy from the rocks and building the varnish’s hard outer crust, Cleland suggests. Some scientists, for instance, think manganese-oxidizing bacteria or fungi might be responsible for concentrating iron and manganese oxides to create the stains. Unknown microbes may cement the metals with clay and silicate particles to produce the varnish’s shellac. Scientists have tried and failed to re-create desert varnish in the lab using fungi and bacteria.
Critics say that varnishes form too slowly — over thousands of years — to be a microbial process and that oxidizing manganese doesn’t generate enough energy to live on. Desert varnish is most likely a product of physical chemistry, they say.

But that criticism shows bias, Cleland responds. “We have an assumption that life on Earth has a pace,” she says. Shadow life may grow far more leisurely, making it hard for scientists to classify it as alive.

One way to determine whether the varnish has a biological or geologic origin is to measure isotope ratios, Cleland says. Isotopes are forms of elements with differing numbers of neutrons in the nuclei of their atoms. Lighter isotopes, with fewer neutrons, are favored by some biochemical reactions.

“Life is lazy,” says Cleland. “It doesn’t want to haul around an extra neutron.” Concentrations of lighter isotopes could signal the handiwork of living organisms, she notes.

Mineral distortions
To find life, and classify it correctly, look for the odd thing out, suggests Hazen, who is looking for messages in minerals. Minerals on Earth are unevenly distributed, he and colleagues have determined. There are 4,933 recognized minerals on the planet. Hazen and colleagues mapped the locations of 4,831 of them and found that 22 percent exist in only one location (SN Online: 12/8/14). Close to 12 percent occur in only two places, the researchers reported last year in The Canadian Mineralogist.

One reason for the skewed distribution is that evolving life has used local resources and concentrated them into new minerals. Take for example hazenite, named for Hazen. The phosphate mineral is produced only by microbes living in California’s Mono Lake. Actions of other species in other places on Earth have combined with the planet’s geology to make Earth’s mineralogy unique, Hazen wrote with colleagues last year in Earth and Planetary Science Letters.

Finding similarly distorted distributions of minerals on other planets or moons could indicate that life exists, or once existed, there. Hazen has advised NASA on how rovers might identify mineral clues to life on Mars.
But determining whether something is unusual might not be as easy as it sounds. Scientists don’t yet know enough about the environment of Mars, Benner says. “Every rover has given us surprises.” He’d like to see a manned fact-finding mission, which he says might lead to a better understanding of the Red Planet and speed up the search for life there.

Mars was once wet (SN Online: 10/8/15) and still has occasional running water (SN: 10/31/15, p. 17). That and other mounting evidence that the Red Planet was once capable of supporting life led Benner to hypothesize in 2013 that Mars may have seeded life on Earth. Whether that hypothesis holds may depend on finding Martians, but Benner doesn’t seem worried.

“I think I would be surprised now if they don’t find life on Mars,” he says. Once the announcement is made, researchers will begin fighting over whether the Martians are real, he predicts. “It will be a good-natured fight because everybody wants to find life, but everybody is aware of the pitfalls of experiments conducted at a 100-million-mile distance by robots.”

Manned missions could easily reach Mars to confirm a find, says Dirk Schulze-Makuch, an astrobiologist at Washington State University in Pullman. “If you have a human with a microscope and the microbe is wiggling and waving back, that’s really hard to refute,” he jokes.

But humans and even probes may have a harder time spotting life on more distant or exotic locales, such as the moons of Jupiter and Saturn. Europa, Enceladus and Titan are frigid places barely kissed by the sun’s energetic rays, but that doesn’t mean they are devoid of life, Schulze-Makuch says. ET hunters are particularly attracted to Europa and Enceladus because liquid oceans slosh beneath their icy crusts. Liquid water is thought to be necessary for many of the chemical reactions that could support life, so it’s one of the primary things astronomers look for.

Going for the less obvious
But water is actually a terrible solvent for forming complex molecules on which life could be based, Schulze-Makuch says. Instead, he thinks, really alien aliens might have spawned at hot spots deep in the hydrocarbon lakes of Saturn’s biggest moon, Titan. There, “you could make something very intriguing. Whether you can get all the way to life, we don’t know,” he says. If he sent a probe to that moon, he would first look for large macro-molecules similar to the DNA, RNA and proteins that Earth life uses, but with a Titanic twist.

He has been studying a natural asphalt lake in Trinidad to learn more about what life in Titan’s lakes might be like. Last July in the journal Life, he and colleagues laid out the physical, chemical and physiological limits that life on Titan would bump up against.

Perhaps the biggest challenge for Titanic life is the extreme cold, says chemical engineer Paulette Clancy of Cornell University. Frosty Titan is so cold that methane — a gas on balmy Earth — is a viscous, almost-freezing liquid, and water “would be like a rock,” she says. Under those conditions, organisms with Earth-like chemistry wouldn’t stand a chance.
For one thing, the membranes that hold in a cell’s guts on Earth wouldn’t work on Titan. Membranes are made of twin sheets of chainlike molecules each with an oxygen-containing head and a long tail of fatty acids. “On Titan,” says Clancy, “long chains would be a disadvantage because they would be frozen in place,” making membranes brittle. Plus, Titan has no free oxygen to form the molecules’ traditional heads.

But Clancy and her Cornell colleagues, chemical engineer James Stevenson and astronomer Jonathan Lunine, simulated experiments under Titan-like conditions. (Molecules that would be stable on Titan would fall apart on Earth, so the researchers had to do computer experiments instead of synthesizing the molecules in a lab.) Short-tailed acrylonitrile molecules with nitrogen-containing heads could spontaneously create stable bubbles called azotosomes, the researchers reported last year in Science Advances. The bubbles are similar to cell membranes.

“Azo” is a prefix that denotes a particular configuration of nitrogen atoms in a molecule. It’s also Greek for “without life.” The word’s meaning “would be ironic if life on Titan were based … on nitrogen,” Clancy says.

Like desert varnish, life on Titan may have unfamiliar pacing that could prevent Earthlings from determining whether azotosomes or other membranous bubbles found in that moon’s methane oceans actually harbor life. With little solar radiation to stimulate evolution and frigid temperatures to slow chemical reactions, life on Titan may be really poky, Schulze-Makuch says. He imagines that Titanic life-spans may stretch to millions of years, with organisms reproducing or even breathing only once every thousand years. Scientists may need to measure metabolic reactions instead of generation times to determine whether something is living on Saturn’s frigid satellite.

Clancy hopes to explore what types of metabolism Titan’s chemistry might allow. Neptune’s icy moon Triton, which is covered in a thin veneer of nitrogen and methane and has nitrogen-spewing geysers, may also be a candidate for new and exciting biochemistry, she says.

With so many options out there, Clancy predicts that there are several planets or moons with life on them. “That we have the lock on the way life decided to develop, I think, is unlikely.”

Many other researchers are also optimistic that life is out there to find. “I think life is a cosmic imperative,” Hazen says. Someday, astrobiologists may come face-to-face with ET. Maybe they will even recognize it when they see it.