Water Was Present During Birth of Earth, Study of Silver Suggests

Tiny variations in the isotopic composition of silver in meteorites and Earth rocks are helping scientists put together a timetable of how our planet was assembled beginning 4.568 billion years ago. The new study, published in the journal Science, indicates that water and other key volatiles may have been present in at least some of Earth's original building blocks, rather than acquired later from comets, as some scientists have suggested.
Compared to the Solar System as a whole, Earth is depleted in volatile elements, such as hydrogen, carbon, and nitrogen, which likely never condensed on planets formed in the inner, hotter, part of the Solar System. Earth is also depleted in moderately volatile elements, such as silver.

"A big question in the formation of the Earth is when this depletion occurred," says co-author Richard Carlson of the Carnegie Institution for Science's Department of Terrestrial Magnetism. "That's where silver isotopes can really help."

Silver has two stable isotopes, one of which, silver-107 was produced in the early Solar System by the rapid radioactive decay of palladium-107. Palladium-107 is so unstable that virtually all of it decayed within the first 30 million years of the Solar System's history.

Silver and palladium differ in their chemical properties. Silver is the more volatile of the two, whereas palladium is more likely to bond with iron. These differences allowed the Carnegie researchers, which included Carlson lead author Maria Schönbächler (a former Carnegie Institution postdoctoral scientist now at the University of Manchester) Erik Hauri, Mary Horan, and Tim Mock to use the isotopic ratios in primitive meteorites and rocks from Earth's mantle to determine the history of Earth's volatiles relative to the formation of Earth's iron core. Other evidence, specifically from hafnium and tungsten isotopes, indicates that the core formed between 30 to 100 million years after the origin of the Solar System.

"We found that the silver isotope ratios in mantle rocks from the Earth exactly matched those in primitive meteorites," says Carlson. "But these meteorites have compositions that are very volatile-rich, unlike the Earth, which is volatile-depleted."

The silver isotopes also presented another riddle, suggesting that the Earth's core formed about 5-10 million years after the origin of the Solar System, much earlier than the date from the hafnium-tungsten results.

The group concludes that these contradictory observations can be reconciled if Earth first accreted volatile-depleted material until it reached about 85% of its final mass and then accreted volatile-rich material in the late stages of its formation, about 26 million years after the Solar System's origin. The addition of volatile-rich material could have occurred in a single event, perhaps the giant collision between the proto-Earth and a Mars-sized object thought to have ejected enough material into Earth orbit to form the Moon.

The results of the study support a 30-year old model of planetary growth called "heterogeneous accretion," which proposes that the Earth's building blocks changed in composition as the planet accreted. Carlson adds that it would have taken just a small amount of volatile-rich material similar to primitive meteorites added during the late stages of Earth's accretion to account for all the volatiles, including water, on the Earth today.

Mutant All-Black Penguin Found

Why Deep–Sea Creatures Glow

Whatever Happened to the Ozone Hole?

What would the 1980s have been without big hair and ice-cold wine coolers?

Luckily no one had to find out: Key substitutions in hairsprays and refrigerants allowed such products to exist without chlorofluorocarbons (CFCs), which were found to be ripping a huge "hole" in Earth's protective ozone layer.

Today the ozone hole, which was first spotted 25 years ago, appears headed for a happy ending, thanks to unprecedented international action.

Could a similar effort rein in climate change? And is the closing ozone hole actually making global warming worse?

Ozone at High Risk From CFCs

The ozone layer lies between about 9.3 and 18.6 miles (15 and 30 kilometers) above Earth's surface. This blanket of ozone, or O3, blocks most of the sun's high-frequency ultraviolet rays.

These UV rays can cause skin cancer and cataracts in humans, as well as reproductive problems in fish, crabs, frogs, and even in the single-celled phytoplankton at the bottom of the ocean food chain.

Ozone is created naturally when oxygen molecules (O2) high in the atmosphere get broken by sunlight into two free oxygen atoms. A free atom can then bond with an unbroken O2 molecule, and ozone is born.

Ozone is unstable, however, and it's easily broken up by trace elements.

Invented in the 1920s, CFCs proved to be an exceptional problem for ozone, because many of these synthetic chemicals can persist for decades, allowing them to make their way into the upper atmosphere. (Related: "Rocket Launches Damage Ozone Layer, Study Says.")

In that rarefied air, ultraviolet light breaks the molecular bonds in CFCs and free chlorine atoms get released. Chlorine then destroys ozone molecules by "stealing" their oxygen atoms.

Ozone Hole a Shocking Surprise

Scientists had theorized since the 1970s about the chemistry that could lead to ozone depletion. But in May 1985 scientists with the British Antarctic Survey shocked the world when they announced the discovery of a huge hole in the ozone layer over Antarctica.

Technically a substantial thinning of the ozone layer, the ozone "hole" has been opening every spring since the 1970s, the scientists reported.

Their data, collected at the Halley Research Station in Antarctica, suggested that CFCs were to blame. That's because atmospheric conditions during the cold, dark, Antarctic winters were building stockpiles of CFCs over the South Pole.

Returning spring sunshine would then spawn an abundance of free chlorine, depleting ozone levels above Antarctica by as much as 65 percent. (Related: "Laughing Gas Biggest Threat to Ozone Layer, Study Says.")

"One lesson is that the planet can change very rapidly in an unexpected way," said Jonathan Shanklin, one of the British scientists who made the ozone hole discovery and co-author of a paper on the ozone hole anniversary appearing in this week's issue of the journal Nature.

"Nobody was expecting to see anything like this in the Antarctic."

Fixing the Ozone Hole a Unanimous Decision

The disturbing discovery set the stage for an environmental triumph: the Montreal Protocol of 1987.

This pact to phase out the use of CFCs and restore the ozone layer was eventually signed by every country in the United Nations—the first UN treaty to achieve universal ratification.

The unparalleled cooperation has had a major impact.

"If we had just kept letting CFCs increase at a pretty nominal rate, characteristic of the 1970s, the decreased ozone levels of the hole would have eventually covered the entire planet," said atmospheric physicist Paul Newman of NASA's Goddard Space Flight Center.

"Global ozone dropped a little bit [after CFCs were banned], but the good news is that if we had done nothing, it would have gotten really, really bad."

Now a complete rebound seems imminent. Some scientists project that by 2080 global ozone will return to 1950s levels.

Now How About Global Warming?

As climate scientists around the globe urge action to curb greenhouse gas emissions, might the ozone hole experience provide some useful parallels? Perhaps, experts say—but the situations do have some significant differences.

In the 1980s people were faced with the clear and present health dangers from ozone depletion, leading to widespread public support for CFC bans.

"There was a scary side of the ozone hole, linked to skin cancers and cataracts and so on, which immediately engaged the public," the British Antarctic Survey's Shanklin said. "The real impact of what a rapidly warming world could do is not so obviously intuitive."

Chemical manufacturers were also able to create substitutes for CFCs with little added costs, enabling governments to address the problem without great impacts on the economy or average lifestyle.

Global warming, on the other hand, has become a politically loaded and often divisive topic.

And many potential fixes to the problem—such as alternative energies and reduced consumption—could cause major disruptions to economic and geopolitical norms in a way that replacing CFCs simply did not, Shanklin said.

Ozone Recovery to Warm Antarctica?

Meanwhile, some scientists say the environmental triumph of a recovering ozone layer could have a troubling side effect: boosting global warming, at least in the Antarctic region.

Ozone itself is a greenhouse gas. A thinner ozone layer not only reduced heat trapped over the region, it helped stir circumpolar winds, which in turn created sea spray that formed reflective, cooling clouds.

"It's very difficult to quantify the impact on a global scale, but I think the evidence suggests filling the hole will have a regional effect on the Antarctic, possibly leading to more warming for the bulk of the Antarctic," Shanklin said. "That could drastically change predictions about global sea level change."

Ken Carslaw of the U.K.'s University of Leeds was a co-author on the study that suggested closing the ozone hole would lead to a bump in Antarctic warming. Still, he thinks that any warming mitigation produced by the ozone hole was merely a side effect and not a net gain.

"I wouldn't say that these discoveries [of possible warming] suggest the formation of the ozone hole was a good thing," he said.

NASA's Newman agreed: "The consequences of unabated CFC growth were disastrous for life," he said.

"So at some point you had to act, and fortunately they acted before it became a really severe problem. We never got to the level of an environmental catastrophe.

"It really is a testament to the good science that went into [understanding] the ozone hole and the nerve of the politicians to act on that science."

New Study Ranks Countries on Environmental Impact

Relative rank of countries by proportional and absolute environmental impact: Proportional environmental impact (179 countries; top panel) and absolute environmental impact rank (171 countries; bottom panel) (darker grey = higher impact) out of 228 countries considered are shown. Environmental impact ranks (proportional and absolute) combine ranks for natural forest lost, habitat conversion, marine captures, fertilizer use, water pollution, carbon emissions and proportion of threatened species (see text for details). The worst 20 countries for each ranking are shown.

A new study led by the University of Adelaide's Environment Institute in Australia has ranked most of the world's countries for their environmental impact.
The research uses seven indicators of environmental degradation to form two rankings -- a proportional environmental impact index, where impact is measured against total resource availability, and an absolute environmental impact index measuring total environmental degradation at a global scale.

Led by the Environment Institute's Director of Ecological Modelling Professor Corey Bradshaw, the study has been published in the on-line, peer-reviewed science journal PLoS ONE.

The world's 10 worst environmental performers according to the proportional environmental impact index (relative to resource availability) are: Singapore, Korea, Qatar, Kuwait, Japan, Thailand, Bahrain, Malaysia, Philippines and Netherlands.

In absolute global terms, the 10 countries with the worst environmental impact are (in order, worst first): Brazil, USA, China, Indonesia, Japan, Mexico, India, Russia, Australia and Peru.

The indicators used were natural forest loss, habitat conversion, fisheries and other marine captures, fertiliser use, water pollution, carbon emissions from land use and species threat.

"The environmental crises currently gripping the planet are the corollary of excessive human consumption of natural resources," said Professor Bradshaw. "There is considerable and mounting evidence that elevated degradation and loss of habitats and species are compromising ecosystems that sustain the quality of life for billions of people worldwide."

Professor Bradshaw said these indices were robust and comprehensive and, unlike existing rankings, deliberately avoided including human health and economic data - measuring environmental impact only.

The study, in collaboration with the National University of Singapore and Princeton University, found that the total wealth of a country (measured by gross national income) was the most important driver of environmental impact.

"We correlated rankings against three socio-economic variables (human population size, gross national income and governance quality) and found that total wealth was the most important explanatory variable - the richer a country, the greater its average environmental impact," Professor Bradshaw said.

There was no evidence to support the popular idea that environmental degradation plateaus or declines past a certain threshold of per capital wealth (known as the Kuznets curve hypothesis).

"There is a theory that as wealth increases, nations have more access to clean technology and become more environmentally aware so that the environmental impact starts to decline. This wasn't supported," he said.

Neanderthal Genome Yields Insights Into Human Evolution and Evidence of Interbreeding With Modern Humans

After extracting ancient DNA from the 40,000-year-old bones of Neanderthals, scientists have obtained a draft sequence of the Neanderthal genome, yielding important new insights into the evolution of modern humans.
Among the findings, published in the May 7 issue of Science, is evidence that shortly after early modern humans migrated out of Africa, some of them interbred with Neanderthals, leaving bits of Neanderthal DNA sequences scattered through the genomes of present-day non-Africans.

"We can now say that, in all probability, there was gene flow from Neanderthals to modern humans," said the paper's first author, Richard E. (Ed) Green of the University of California, Santa Cruz.

Green, now an assistant professor of biomolecular engineering in the Baskin School of Engineering at UC Santa Cruz, began working on the Neanderthal genome as a postdoctoral researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Svante Pääbo, director of the institute's genetics department, leads the Neanderthal Genome Project, which involves an international consortium of researchers. David Reich, a population geneticist at the Broad Institute of MIT and Harvard, also played a leading role in the new study and the ongoing investigation of the Neanderthal genome.

"The Neanderthal genome sequence allows us to begin to define all those features in our genome where we differ from all other organisms on the planet, including our closest evolutionary relative, the Neanderthals," Pääbo said.

The researchers identified a catalog of genetic features unique to modern humans by comparing the Neanderthal, human, and chimpanzee genomes. Genes involved in cognitive development, skull structure, energy metabolism, and skin morphology and physiology are among those highlighted in the study as likely to have undergone important changes in recent human evolution.

"With this paper, we are just scratching the surface," Green said. "The Neanderthal genome is a goldmine of information about recent human evolution, and it will be put to use for years to come."

Neanderthals lived in much of Europe and western Asia before dying out 30,000 years ago. They coexisted with humans in Europe for thousands of years, and fossil evidence led some scientists to speculate that interbreeding may have occurred there. But the Neanderthal DNA signal shows up not only in the genomes of Europeans, but also in people from East Asia and Papua New Guinea, where Neanderthals never lived.

"The scenario is not what most people had envisioned," Green said. "We found the genetic signal of Neanderthals in all the non-African genomes, meaning that the admixture occurred early on, probably in the Middle East, and is shared with all descendants of the early humans who migrated out of Africa."

The study did not address the functional significance of the finding that between 1 and 4 percent of the genomes of non-Africans is derived from Neanderthals. But Green said there is no evidence that anything genetically important came over from Neanderthals. "The signal is sparsely distributed across the genome, just a 'bread crumbs' clue of what happened in the past," he said. "If there was something that conferred a fitness advantage, we probably would have found it already by comparing human genomes."

The draft sequence of the Neanderthal genome is composed of more than 3 billion nucleotides--the "letters" of the genetic code (A, C, T, and G) that are strung together in DNA. The sequence was derived from DNA extracted from three Neanderthal bones found in the Vindiga Cave in Croatia; smaller amounts of sequence data were also obtained from three bones from other sites. Two of the Vindiga bones could be dated by carbon-dating of collagen and were found to be about 38,000 and 44,000 years old.

Deriving a genome sequence--representing the genetic code on all of an organism's chromosomes--from such ancient DNA is a remarkable technological feat. The Neanderthal bones were not well preserved, and more than 95 percent of the DNA extracted from them came from bacteria and other organisms that had colonized the bone. The DNA itself was degraded into small fragments and had been chemically modified in many places.

The researchers had to develop special methods to extract the Neanderthal DNA and ensure that it was not contaminated with human DNA. They used new sequencing technology to obtain sequence data directly from the extracted DNA without amplifying it first. Although genome scientists like to sequence a genome at least four or five times to ensure accuracy, most of the Neanderthal genome has been covered only one to two times so far.

The draft Neanderthal sequence is probably riddled with errors, Green said, but having the human and chimpanzee genomes for comparison makes it extremely useful despite its limitations. Places where humans differ from chimps, while Neanderthals still have the ancestral chimp sequence, may represent uniquely human genetic traits. Such comparisons enabled the researchers to catalog the genetic changes that have become fixed or have risen to high frequency in modern humans during the past few hundred thousand years.

"It sheds light on a critical time in human evolution since we diverged from Neanderthals," Green said. "What adaptive changes occurred in the past 300,000 years as we were becoming fully modern humans? That's what I find most exciting. Right now we are still in the realm of identifying candidates for further study."

The ancestral lineages of humans and chimpanzees are thought to have diverged about 5 or 6 million years ago. By analyzing the Neanderthal genome and genomes of present-day humans, Green and his colleagues estimated that the ancestral populations of Neanderthals and modern humans separated between 270,000 and 440,000 years ago.

The evidence for more recent gene flow between Neanderthals and humans came from an analysis showing that Neanderthals are more closely related to some present-day humans than to others. The researchers looked at places where the DNA sequence is known to vary among individuals by a single "letter." Comparing different individuals with Neanderthals, they asked how frequently the Neanderthal sequence matches that of different humans.

The frequency of Neanderthal matches would be the same for all human populations if gene flow between Neanderthals and humans stopped before human populations began to develop genetic differences. But that's not what the study found. Looking at a diverse set of modern humans--including individuals from Southern Africa, West Africa, Papua New Guinea, China, and Western Europe--the researchers found that the frequency of Neanderthal matches is higher for non-Africans than for Africans.

According to Green, even a very small number of instances of interbreeding could account for these results. The researchers estimated that the gene flow from Neanderthals to humans occurred between 50,000 and 80,000 years ago. The best explanation is that the admixture occurred when early humans left Africa and encountered Neanderthals for the first time.

"How these peoples would have interacted culturally is not something we can speculate on in any meaningful way. But knowing there was gene flow is important, and it is fascinating to think about how that may have happened," Green said.

The researchers were not able to rule out one possible alternative explanation for their findings. In that scenario, the signal they detected could represent an ancient genetic substructure that existed within Africa, such that the ancestral population of present-day non-Africans was more closely related to Neanderthals than was the ancestral population of present-day Africans. "We think that's not the case, but we can't rule it out," Green said.

The researchers expect many new findings to emerge from ongoing investigations of the Neanderthal genome and other ancient genetic sequences. Pääbo's group recently found evidence of a previously unknown type of hominid after analyzing DNA extracted from what they had thought was a Neanderthal finger bone found in Siberia. Green is also taking part in that continuing investigation.

Trapping Giant Rydberg Atoms for Faster Quantum Computers

In an achievement that could help enable fast quantum computers, University of Michigan physicists have built a better Rydberg atom trap. Rydberg atoms are highly excited, nearly-ionized giants that can be thousands of times larger than their ground-state counterparts.
As a result of their size, interactions between Rydberg atoms can be roughly a million times stronger than between regular atoms. This is why they could serve as faster quantum circuits, said Georg Raithel, associate chair and professor in the Department of Physics. Quantum computers could solve problems too complicated for conventional computers. Many scientists believe that the future of computation lies in the quantum realm.

A paper on this research is published in the current edition of Physical Review Letters. The work will be presented at the American Physical Society's Division of Atomic, Molecular and Optical Physics meeting in late May.

Raithel's team trapped the atoms in what's called an optical lattice -- a crate made of interfering laser beams.

"The optical lattice is better than any other Rydberg atom trap for quantum information processing or high-precision spectroscopy," Raithel said. "Compared with other traps, optical lattices minimize energy level shifts in the atoms, which is important for these applications."

Raithel and physics doctoral students Kelly Younge and Sarah Anderson started with ground-state atoms of the soft metal rubidium. At room temperature, the atoms whiz around at the speed of sound, about 300 meters per second. The researchers hit them with lasers to cool and slow them to 10 centimeters per second.

"That's about the speed of a mosquito," Younge said. "Cooling lasers combined with a magnetic field allows us to trap the ground-state atoms. Then we excite the atoms into Rydberg states."

In a rubidium atom, just one electron occupies the outer valence shell. With precisely tuned lasers, the researchers excited this electron so that it moved 100 times farther away from the nucleus of the atom, which classified it as a Rydberg atom. That valence electron in this case is so far away from the nucleus that it behaves almost as if it's a free electron.

To trap the Rydberg atoms, the researchers took advantage of what's called the "ponderomotive force" that allows them to secure a whole atom by holding fast to one electron -- the sole valence shell particle in the rubidium Rydberg atoms. The optical lattice, formed with intense, interfering laser beams, is what provides the ponderomotive force.

"The laser field holds on to the electron, which behaves almost as if it were free, but the residual weak atomic binding force still holds the atom together. In effect, the entire atom is trapped by the lasers," Raithel said.

The physicists used a technique called "microwave spectroscopy," to determine how the lattice affected the Rydberg atoms, and in general how the atoms behaved in the trap.

"Essentially, we could track the motion of the atoms during the experiment. We could tell if the atoms were sitting in the bottom of a well in the electromagnetic field, or if they were roaming over many wells. In this way, we could optimize the performance of the trap," Younge said.

The paper is called "State-dependent Energy Shifts of Rydberg Atoms in a Ponderomotive Optical Lattice."

This research is funded by the National Science Foundation and the National Defense Science and Engineering Graduate Fellowship Program.

Gulf Oil Spill Pictures: Aerial Views Show Leak's Size

A boat makes its way through crude oil on the water's surface on Wednesday, about a week after the Deepwater Horizon oil rig sank into the Gulf of Mexico. Even now authorities can only guess at the size of the spill, because the ongoing leak is deep underwater.

Most large oil spills in history stemmed from tanker accidents, and their sizes could be reckoned based on the holding capacity of the wrecked vessels.

Oil company BP, which owns the leaking well, provided the original estimate of a thousand barrels a day, based on underwater cameras that recorded the flow from leaks 5,000 feet (1,524 meters) below water.

But the U.S. National Oceanic and Atmospheric Administration, or NOAA, which has also been monitoring the disaster on the scene and from the air, now says evidence points to the spill being five times worse—about 5,000 barrels a day. BP says it has identified a potentially new leak in the damaged pipes on the sea floor, which it had not seen before.

Toothy Texas Pterosaur Discovered; Soared Over Dallas

Long before six flags flew over Texas, a newfound species of winged reptile with an exceptionally toothy grin owned the skies over what is now the Lone Star State.

The recently discovered pterosaur, dubbed Aetodactylus halli, was identified based on a 95-million-year-old lower jawbone found outside of Dallas by amateur fossil hunter Lance Hall. The pterosaur had a relatively slender jaw filled with thin, needlelike teeth, which might have helped the creature pluck fish from the shallow sea that once covered the region, a new study says.

"It was hanging out near the ocean, and that is probably where it derived its food from," said study leader Timothy Myers, a paleontologist at Southern Methodist University in Dallas.

By comparing the jawbone to more complete pterosaur fossils, Myers and his team think A. halli was a medium-size animal with a nine-foot (three-meter) wingspan and a short tail.

Texas's Toothy Pterosaur a Rare Find

Pterosaurs ruled the skies from the late Triassic period, more than 200 million years ago, until dinosaurs went extinct at the end of the Cretaceous, about 65 million years ago.

At 95 million years old, A. halli is one of the youngest members yet found in the Ornithocheiridae family of toothed pterosaurs, Myers said.

Despite being common elsewhere in the world, toothed pterosaur fossils are rare in Texas: A. halli is only the second ornithoceirid yet discovered in North America.

The new pterosaur had 54 teeth in its lower jaw, which is an unusual amount for ornithoceirids, Myers added. Most other members of the family had just 30 lower jaw teeth. Only Boreopterus, a relative from the same time period found in China, is known to have had as many teeth as A. halli.

When the animal lived, a giant north-south interior seaway split North America from the Gulf of Mexico to the Arctic Ocean, putting what is now Dallas underwater.

A. halli's jawbone was found in marine rocks exposed near a highway in Mansfield, southwest of Dallas (see map), which would have been the southernmost end of the ancient sea. No other fossils from the animal have been unearthed nearby, Myers said.

"It could be that something caused the pterosaur to die and fall into the water," he said. "Decay started, and the lower jaw just fell off and got separated from the rest of the body."

Mass Extinctions What Causes Animal Die-Offs?

More than 90 percent of all organisms that have ever lived on Earth are extinct. As new species evolve to fit ever changing ecological niches, older species fade away. But the rate of extinction is far from constant. At least a handful of times in the last 500 million years, 50 to more than 90 percent of all species on Earth have disappeared in a geological blink of the eye.

Though these mass extinctions are deadly events, they open up the planet for new life-forms to emerge. Dinosaurs appeared after one of the biggest mass extinction events on Earth, the Permian-Triassic extinction about 250 million years ago. The most studied mass extinction, between the Cretaceous and Paleogene periods about 65 million years ago, killed off the dinosaurs and made room for mammals to rapidly diversify and evolve.

The causes of these mass extinction events are unsolved mysteries, though volcanic eruptions and the impacts of large asteroids or comets are prime suspects in many of the cases. Both would eject tons of debris into the atmosphere, darkening the skies for at least months on end. Starved of sunlight, plants and plant-eating creatures would quickly die. Space rocks and volcanoes could also unleash toxic and heat-trapping gases that—once the dust settled—enable runaway global warming.

An extraterrestrial impact is most closely linked to the Cretaceous extinction event. A huge crater off Mexico's Yucatán Peninsula is dated to about 65 million years ago, coinciding with the extinction. Global warming fueled by volcanic eruptions at the Deccan Flats in India may also have aggravated the event. Whatever the cause, dinosaurs, as well as about half of all species on the planet, went extinct.

Massive floods of lava erupting from the central Atlantic magmatic province about 200 million years ago may explain the Triassic-Jurassic extinction. About 20 percent of all marine families went extinct, as well as most mammal-like creatures, many large amphibians, and all non-dinosaur archosaurs. An asteroid impact is another possible cause of the extinction, though a telltale crater has yet to be found.

Largest Ever Die-Off

The Permian-Triassic extinction event about 250 million years ago was the deadliest: More than 90 percent of all species perished. Many scientists believe an asteroid or comet triggered the massive die-off, but, again, no crater has been found. Another strong contender is flood volcanism from the Siberian Traps, a large igneous province in Russia. Impact-triggered volcanism is yet another possibility.

Starting about 360 million years ago, a drawn-out event eliminated about 70 percent of all marine species from Earth over a span of perhaps 20 million years. Pulses, each lasting 100,000 to 300,000 years, are noted within the larger late Devonian extinction. Insects, plants, and the first proto-amphibians were on land by then, though the extinctions dealt landlubbers a severe setback.

The Ordovician-Silurian extinction, about 440 million years ago, involved massive glaciations that locked up much of the world's water as ice and caused sea levels to drop precipitously. The event took its hardest toll on marine organisms such as shelled brachiopods, eel-like conodonts, and the trilobites.

Happening Now?

Today, many scientists think the evidence indicates a sixth mass extinction is under way. The blame for this one, perhaps the fastest in Earth's history, falls firmly on the shoulders of humans. By the year 2100, human activities such as pollution, land clearing, and overfishing may have driven more than half of the world's marine and land species to extinction.

Supernova's Beginning Blast Shown in 3-D—A First

The mysterious first moments of a supernova have now been modeled in 3-D—showing what happens in a dying star's heart from half a second to about two hours after the blast begins.

The development could help scientists eventually "rewind" the leftovers of real cataclysmic star explosions to find out how they get started and why their leftovers assume a variety of shapes. (See supernova pictures.)

"These are the first three-dimensional models linking the beginning of the explosion to the supernova structure we see hours later," said study co-author Hans-Thomas Janka, an astrophysicist at the Max Planck Institute for Astronomy in Garching, Germany.

The new simulations also give the best peek yet at the prime suspect in the mystery of what kills big stars from the inside out: a torrential spasm of ghostly subatomic particles called neutrinos.

Supernova's Hidden Heart

Stars fuse hydrogen into helium deep down at their hearts. Very massive stars have enough oomph to continue fusing helium into progressively heavier elements, a process that results in onionlike layers, from lighter hydrogen at the surface to dense iron at the core.

When these stars run out of fuel, their cores collapse, and they explode in what are known as Type II supernovae. The blasts are so powerful that the supernovae outshine their entire host galaxies for a few days.

But the physics of supernova triggers are poorly understood, because we can't see that deeply into a star.

"The first time you can see the explosion is when it reaches the surface of the star," said Armin Rest, an astrophysicist at Harvard University who was not involved in the work. Our sun won't go supernova—that requires a star about nine times heftier. But if it did, Rest said, "we wouldn't know for the first hour," because hot plasma around the star's core would absorb evidence of the turmoil below.

The new 3-D model, to be described in the May 10 issue of The Astrophysical Journal, is based on theoretical physics derived from observations of real supernovae. According to Rest, the simulation offers unprecedented detail about what's happening in a dying star's interior.

"I think this work is really exciting," Rest said, adding that Janka and his team's model "is at the forefront" of supernova simulations.

Dying Star's Inner Turmoil

With a little more computer crunching, Janka and others in the field hope to use the new model like a forensic investigation tool, examining the shape of debris left after a real star explosion to trace its exact trigger.

As seen from Earth, the remnants of Type II supernovae range from lopsided "puffballs" like Cassiopeia A to spindly structures like the Crab Nebula. The remnants often feature "bullets" of nickel, iron, and other heavy elements that must have punched through the stars' outer layers during the explosion.

The most widely accepted explanation for what sets off a supernova—and leads to asymmetric remnants—is a storm of neutrinos in the dying star's core, said Stan Woosley, an astrophysicist at University of California, Santa Cruz, who also wasn't part of the new work.

Stars keep their spherical shapes because the pull of gravity holding their matter together is counterbalanced by an outward push coming from the energy released as elements go through fusion inside.

At the start of a Type II supernova, the theory goes, a star's iron core gets too massive for its own good, and it gives in to gravity's pull.

The iron core instantly squashes itself into a superdense wad, smashing together protons and electrons to form neutrons—spewing out a horde of neutrinos.

The layer of matter directly above the core falls suddenly into the core, triggering a cascade in which the star's layers gradually fall inward. Infalling matter smacks into the dense core and rebounds, sending a rush of neutrinos to collide with the falling layers above.

These hard-to-detect particles are thought to "boil" any matter in their way, mixing the matter into an uneven brew. The resulting chaos shoots "bullets" of heavy materials out through the collapsing layers.

Ultimately, the shockwave from the core's collapse causes the mixed-up star to explode, leading to oddball remnants. (Related pictures: "'Fossil' Fireballs Found in Supernova Debris.

Supercomputers to Solve Supernova Mysteries

Previous 2-D models were able to show neutrinos triggering supernovae, but the 3-D simulation literally adds a whole new dimension—making for the most realistic-looking supernova simulations to date.

Still, the physics aren't yet detailed enough to be completely realistic, Woosley said.

"This is where the big money is," he said of the computing costs, noting that crunching supernovae models is one of the biggest uses of supercomputer time in the world.

If supernovae theorists like Janka could make a computing wish, what would they ask for?

"Three or four months of nonstop computing time on about 50,000 processors," Janka said—equal to the power of 25,000 of the best dual-core desktop computers. NASA's Pleiades 973-teraflop supercomputer might meet such demands, but it's shared by 1,500 scientists.

"We're getting there," UCSC's Woosley added. "In a few years … I think we'll have this licked."

Part of Alaska Inundated by Ancient Megafloods

New research indicates that one of the largest fresh-water floods in Earth's history happened about 17,000 years ago and inundated a large area of Alaska that is now occupied in part by the city of Wasilla, widely known because of the 2008 presidential campaign.
The event was one of at least four "megafloods" as Glacial Lake Atna breached ice dams and discharged water. The lake covered more than 3,500 square miles in the Copper River Basin northeast of Anchorage and Wasilla.

The megaflood that covered the Wasilla region released as much as 1,400 cubic kilometers, or 336 cubic miles, of water, enough to cover an area the size of Washington, D.C., to a depth of nearly 5 miles. That water volume drained from the lake in about a week and, at such great velocity, formed dunes higher than 110 feet, with at least a half-mile between crests. The dunes appear on topographical maps but today are covered by roads, buildings and other development.

"Your mind doesn't get around dunes of that size. Obviously the water had to be very deep to form them," said Michael Wiedmer, an Anchorage native who is pursuing graduate studies in forest resources at the University of Washington.

Wiedmer is the lead author of a paper describing the Wasilla-area megaflood, published in the May edition of the journal Quaternary Research. Co-authors are David R. Montgomery and Alan Gillespie, UW professors of Earth and space sciences, and Harvey Greenberg, a computer specialist in that department.

By definition, a megaflood has a flow of at least 1 million cubic meters of water per second (a cubic meter is about 264 gallons). The largest known fresh-water flood, at about 17 million cubic meters per second, originated in Glacial Lake Missoula in Montana and was one of a series of cataclysmic floods that formed the Channeled Scablands of eastern Washington.

The megaflood from Glacial Lake Atna down what is now the Matanuska River to the Wasilla region might have had a flow of about 3 million cubic meters per second. Another suspected Atna megaflood along a different course to the Wasilla region, down the Susitna River, might have had a flow of about 11 million cubic meters per second. The researchers also found evidence for two smaller Atna megafloods, down the Tok and Copper rivers.

Wiedmer, who retired from the Alaska Department of Fish and Game in 2006, began the research in 2005 when he discovered pygmy whitefish living in Lake George, a glacial lake 50 miles from Anchorage. The lake has essentially emptied numerous times in its history and was not thought to support much life. Examination of physical traits indicate those fish are more closely related to pygmy whitefish in three other mountain lakes, all remnants of Lake Atna, than they are to any others of that species. Their existence in Lake George, some distance from the other lakes, is one piece of evidence for a megaflood from Lake Atna.

"Lake Atna linked up with four distinct drainages, and we think that helped it act like a pump for freshwater organisms," he said.

The megaflood also could explain some of the catastrophic damage that occurred in the magnitude 9.2 Great Alaskan Earthquake of 1964. Wiedmer noted that much of Anchorage is built on marine sediments, and one layer of those sediments liquefied and collapsed, allowing the layer above to slide toward the sea. As the upper layer moved toward the water, structures built on top of it collapsed.

Though the marine sediments extend about 200 feet deep, the failure only occurred within a narrow 3-foot layer. Scientists later discovered that layer had been infused with fresh water, which was unexpected in sediments deposited under salt water. The ancient megaflood could account for the fresh water.

"We suspect that this is evidence of the flood that came down the Matanuska," Wiedmer said. "The location is right at the mouth of where the flood came down, and the time appears to be right."

Seamounts Identified as Significant, Unexplored Territory

Scientists from NOAA and Texas A&M University-Corpus Christi were astounded to find that seamounts, mountains that rise from the seafloor, rank as some of the most common ocean habitats in the world. Their findings are published in a new study and reverse previous beliefs about the prevalence of seamounts, which are treasure troves of marine biodiversity.

"Unlike beaches or even coral reefs, most people will never see a seamount, but this study shows that they are clearly one of the predominant ecosystems on the planet," said Peter Etnoyer, Ph.D., principal investigator of the study and marine biologist at NOAA's Center for Coastal Environmental Health and Biomolecular Research. "We can only hope that through this study, people begin to realize what a vast unknown the ocean represents, and what a vital role it plays on Earth."

Although researchers have thoroughly explored some 200 seamounts and mapped and sampled a hundred others, this study is the first to estimate that more than 45,000 seamounts dot the ocean floor worldwide -- a total of roughly 28.8 million square kilometers or an area larger than the continent of South America. The discovery was made possible using satellite altimetry data that measured incredibly slight changes in the sea surface height that, along with statistical analysis models, indicated the presence of these submerged mountains.

"Seamounts are biodiversity 'hotspots', with higher abundance and variety of life forms than the surrounding seafloor," said Tom Shirley, Ph.D., contributing author of the study and a conservation scientist with the Harte Research Institute at Texas A&M University-Corpus Christi. "In fact, new species are observed or collected on nearly every submersible dive." Two dozen new species of corals and sponges, for example, have been collected from seamounts in the Gulf of Alaska since 2002.

Seamounts not only make up the largest area of ocean habitat, they are also highly productive environments that can serve as habitats for important commercial fish species like orange roughy and sablefish.

This research, which is the first-ever comparison of the size of oceanic and land habitats, is featured in the journal Oceanography.

Liquid-Solid Interactions, as Never Before Seen: New Technique Improves Researchers’ Ability to Measure a Key Property of Material Surfaces

Wettability -- the degree to which a liquid either spreads out over a surface or forms into droplets -- is crucial to a wide variety of processes. It influences, for example, how easily a car's windshield fogs up, and also affects the functioning of advanced batteries and fuel-cell systems.
Until now, the only way to quantify this important characteristic of a material's surface has been to measure the shapes of the droplets that form on it, and this method has very limited resolution. But a team of MIT researchers has found a way to obtain images that improves the resolution of such measurements by a factor of 10,000 or more, allowing for unprecedented precision in determining the details of the interactions between liquids and solid surfaces. In addition, the new method can be used to study curved, textured or complex solid surfaces, something that could not be done previously.

"This is something that was unthinkable before," says Francesco Stellacci, the Paul M. Cook Career Development Associate Professor of Materials Science and Engineering at MIT, leader of the team that developed the new method. "It allows us to make a map of the wetting," that is, a detailed view of exactly how the liquid interacts with the surface down to the level of individual molecules or atoms, as opposed to just the average interaction of the whole droplet.

The new method is described in a paper appearing on April 25 in the journal Nature Nanotechnology. The lead author is postdoctoral fellow Kislon Voïtchovsky, and the paper is coauthored by Stellacci and others at MIT, in England, and in Italy. Stellacci explains that the ability to get such detailed images is important for the study of such processes as catalysis, corrosion and the internal functioning of batteries and fuel cells, and many biological processes such as interactions between proteins.

For example, Voïtchovsky says, in biological research, "you may have a very inhomogeneous sample, with all sorts of reactions going on all over the place. Now we can identify certain specific areas that trigger a reaction."

The method, developed with support from the Swiss National Science Foundation and the Packard Foundation, works by changing the programming that controls an Atomic Force Microscope (AFM). This device uses a sharp point mounted on a vibrating cantilever, which scans the surface of a sample and reacts to topology and the properties of the sample to provide highly detailed images. Stellacci and his team have varied a key imaging parameter: They cause the point to vibrate only a few nanometers (as opposed to tens to hundred of nanometers, which is typical).

"By doing so, you actually improve the resolution of the AFM," Stellacci explains. The resulting resolution, fine enough to map the positions of individual atoms or molecules, is "unmatched before with commercial instruments," he says. Such resolution had been achievable before with very expensive specialized AFMs, of which only a few exist in the world, but can now be equaled by the much more common commercial models, of which there are thousands. Stellacci and his colleagues think the improved resolution results from the way the vibrating tip causes the water to repeatedly push against the surface and dissipate its energy there, but this explanation remains to be tested and confirmed by other researchers.

With their demonstration of both a 10,000-fold improvement in resolution for the specific function of measuring the wetting of surfaces and a 20-fold improvement in overall resolution of the lower-cost AFM, Stellacci says it's not clear which of these applications will end up having more impact.

Arvind Raman, a professor and university faculty scholar in mechanical engineering at Purdue University, agrees that these advances have significant potential. The method demonstrated by this team, which Raman was not involved in, "can routinely achieve atomic resolution on hard surfaces even with commercial AFM systems, and it provides great physical insight into the optimum conditions under which this can be achieved, both of which are very significant achievements," he says. "I really think many in the AFM field will jump on this and try to use the technique."

Raman adds that while the team's interpretation of why the method works as it does offers "one possible mechanism behind the image formation, other plausible mechanisms also exist and will need to be studied in the future to confirm the finding."

Largest Atlas of Nuclear Galactic Rings Unveiled

An international team of astrophysicists has just unveiled the most complete atlas of nuclear rings, enormous star-forming ring-shaped regions that circle certain galactic nuclei. The catalogue, published in the Monthly Notices of the Royal Astronomical Society, includes 113 such rings in 107 galaxies.
"AINUR (the Atlas of Images of Nuclear Rings) is the most complete atlas of nuclear rings created to date," says Sébastien Comerón, a researcher at the Institute of Astrophysics of the Canary Islands (IAC), and co-author of the joint study with other scientists from the universities of La Laguna, Oulu (Finland) and Alabama (United States).

The atlas has just been published in the journal Monthly Notices of the Royal Astronomical Society, and covers 113 nuclear rings in 107 different galaxies. Six are dust rings in elliptical galaxies, while the rest (the majority) are star-forming rings in disc galaxies.

The nuclear rings are ring-shaped, star-forming configurations located around galactic nuclei. They range in size on average from between 500 to 3,000 light years, and they are very bright because they contain an abundance of young stars, including some extremely massive ones. This kind of star has a short lifetime but shines very brightly before exploding as a supernova.

To find the rings, the astrophysicists used images from around 500 galaxies observed by the Hubble space telescope, which belongs to NASA and the European Space Agency, as well as using other references. The images were processed using filters, generating various kinds of maps to help identify the rings more easily.

Rings and Lindblad resonances

"The AINUR atlas has also looked for relationships between the properties of the nuclear rings and those of the galaxies in which they are found," says Comerón, "and we have been able to statistically prove that most rings are associated with Lindblad resonances (gravitational shoves that push objects out of certain orbits and into others)."

The astrophysicists have shown that when the rings are in a barred galaxy (within disc galaxies, which have a central cylinder or 'cigar' of stars), the maximum radius that a nuclear ring can attain is 25% of the length of the bar, and that the maximum radius is inversely proportional to the strength of the bar. This is the behaviour that was predicted for the internal Lindblad resonances, which are determined by the size of the bar and their strength (how elliptical this is). If the bar is small or very elliptical, the resonance orbit becomes small, but if it is large or not very elliptical, the orbits become bigger.

The researchers also found that, contrary to what had been believed until now, a significant proportion of nuclear rings are to be found in non-barred galaxies (around 20%). The resonances needed to form the rings in these galaxies "are probably created by strong spiral arms, weak oval distortions of the disc and some lesser interaction with neighbouring galaxies," the scientists say.