Wednesday, December 9, 2009


0 comentarios

Five ancient crocs, one with teeth like boar tusks and another with a snout like a duck's bill, have been discovered in the Sahara by National Geographic Explorer-in-Residence Paul Sereno and McGill Professor Hans Larsson. The five fossil crocs, three of them newly named species, are remains of a bizarre world of crocs that inhabited the southern land mass known as Gondwana some 100 million years ago.

Sereno, a professor at the University of Chicago, and his team members, including Larsson, unearthed the strange crocs in a series of expeditions beginning in 2000. "These species open a window on a croc world completely foreign to what was living on northern continents," Sereno said. These crocs, along with a closely related sixth species, are detailed in a paper published in the journal ZooKeys and appear in the current issue of National Geographic magazine.

At 40 feet in length and weighing 8 tons, Sarcosuchus imperator, or SuperCroc, was the first and largest of the crocs Sereno found in the Sahara, but it was not the strangest, Sereno said. He and his teams soon discovered key fossils of five previously unknown or poorly understood species, most of them walking "upright" with their arms and legs under the body like a land mammal instead of sprawled out to the sides, bellies touching the ground.

New species:

•BoarCroc: Kaprosuchus saharicus; fossils found in Niger. Twenty-foot-long upright meat eater with an armoured snout for ramming and three sets of dagger-shaped fangs for slicing. Closest relative found in Madagascar.
•RatCroc: Araripesuchus rattoides; fossils found in Morocco. Three-foot-long, upright plant and grub eater. Pair of buckteeth in lower jaw used to dig for food. Closest relative in South America.
•PancakeCroc: Laganosuchus thaumastos; fossils found in Niger and Morocco. Twenty-foot-long, squat fish eater with a three-foot pancake-flat head. Spike-shaped teeth on slender jaws. Likely rested motionless for hours, its jaws open and waiting for prey. Closest relative from Egypt. The scientific paper also names a close relative discovered by the team in Morocco, Laganosuchus maghrebensis.

New fossils:

•DuckCroc: Previously named species, Anatosuchus minor; fossils found in Niger. Three-foot-long upright fish-, frog- and grub-eater. Broad, overhanging snout and Pinocchio-like nose. Special sensory areas on the snout end allowed it to root around on the shore and in shallow water for prey. Closest relative in Madagascar.
•DogCroc: New fossils of named species, Araripesuchus wegeneri; fossils found in Niger include five skeletons, all next to each other on a single block of rock. Three-foot-long upright plant and grub eater with a soft, doglike nose pointing forward. Likely an agile galloper, but also a capable swimmer. Closest relative in Argentina.

"We were surprised to find so many species from the same time in the same place," said Larsson, who along with a team member discovered the bones of BoarCroc and PancakeCroc. "Each of the crocs apparently had different diets, different behaviours. It appears they had divided up the ecosystem, each species taking advantage of it in its own way."

Based on interpretation of the fossils, Sereno and Larsson hypothesize that these early crocs were small, upright gallopers. They suggest that the more agile of their new croc menagerie could not only gallop on land but also evolved a swimming tail for agility and speed in water, two modes of locomotion suggested to be evolutionary hallmarks for the past 200 million years.

To study the crocs' brains, Sereno CT-scanned the skulls of DuckCroc and DogCroc and created digital and physical casts of the brains. The result: Both DogCroc and DuckCroc had broad, spade-shaped forebrains that look different from those of living crocs. "They may have had slightly more sophisticated brain function than living crocs," Larsson said, "because active hunting on land usually requires more brain power than merely waiting for prey to show up."

To collect the croc fossils, Sereno and teams endured temperatures topping 125 degrees F, living for months on dehydrated food. Logistics were challenging: For the 2000 expedition, they transported trucks, tools, tents, five tons of plaster, 600 pounds of water and four months' worth of other supplies.

(Photo: McGill U.)



0 comentarios

Water expands when it freezes. Anyone who has ever left a can of soda or bottle of water in the freezer too long has witnessed this first hand. So how do plants and animals survive severe temperatures?

Insects exposed to subzero temperatures can adapt to the extreme climate to survive freezing temperatures, but until now, antifreeze molecules had not been isolated from freeze-tolerant animals. The NSF-supported study, published in the November 24 issue of Proceedings of the National Academy of Sciences, describes a brand new type of antifreeze molecule isolated from a freeze-tolerant Alaskan beetle by Kent Walters and colleagues at the University of Notre Dame.

Interestingly, the antifreeze molecule described by the research team differs from previously described factors in that it is not a protein, but a combination of saccharides and fatty acids, which are other types of biomolecules. What does that mean? Size is one big difference. The exact size of this particular molecule is unknown, but the fact that it is small could prove beneficial. The chemical composition of the molecule could prove amenable to commercial production because small chains of sugars can be readily synthesized in the laboratory, making them cheaper and easier to manufacture than biologically assembled molecules.

Antifreeze molecules are present in many organisms including fish, insects, plants, fungi and bacteria. "The most active known antifreeze proteins had been described in freeze-avoiding insects, allowing certain insects to survive temperatures below -60 C (-76 F)" said Walters. However, this is the first reported isolation of antifreeze from a freeze-tolerant insect (those able to survive freezing).

One reason is that the antifreeze molecules are not always present. Dropping temperatures serve as a signal that the insects respond to by activating a host of adaptive responses including expression of antifreeze molecules. Researchers can artificially stimulate this response by conditioning the insects before they perform experiments.

Current methods used to cryopreserve tissues result in low viability after thaw, in part because existing solutes must be used at concentrations that are often toxic to cells or tissues. Because the new antifreeze molecule exhibits activity at relatively low concentrations in insects, it is possible researchers may be able to use them at low concentrations in the lab too.

According to Walters, "Potential applications for this new class of antifreeze molecules are abundant. In terms of cryopreservation, we may be able to increase viability and enhance survivorship of cells and tissues from other organisms under freezing conditions."

(Photo: Kent Walters, University of Notre Dame)

National Science Foundation


0 comentarios
Ice sheets are melting more quickly and Arctic sea ice is disappearing much faster than previously projected, and significant sea level rise is more certain than ever, according to a new global scientific synthesis prepared by some of the world's top climate scientists.

In a special report called "The Copenhagen Diagnosis" issued Nov. 24, the 26 researchers, including Eric Steig from the University of Washington, conclude that several important aspects of climate change are occurring as fast as or even faster than expected just a few years ago. The report comes in advance of the Copenhagen climate summit, scheduled for Dec. 7-18.

Steig, a UW professor of Earth and space sciences and a board member of the UW Program on Climate Change, said the report isn't surprising for those who have been following the scientific literature. It provides a considerably more complete picture on several key issues, particularly near-term sea level rise, than the 2007 report from the Intergovernmental Panel on Climate Change, he said.

"It also articulates a much clearer picture of what has to happen if the world wants to keep future warming within the reasonable threshold of 2 degrees Celsius that most scientists believe is prudent," Steig said.

That threshold was agreed upon by leaders of the Group of Eight nations during a summit in July, though the agreement currently is non-binding.

The "Copenhagen Diagnosis," which took a year to complete, is a synthesis of hundreds of research papers about human-induced climate change that have been published since the most recent assessment by the Intergovernmental Panel on Climate Change in 2007. The new report says that satellite and direct measurements show:

-Greenland and Antarctic ice sheets are losing mass and contributing to sea level rise at an increasing rate.
-Arctic sea ice has melted far beyond the expectations of climate models.
-Sea level has risen more than 2 inches in the last 15 years, about 80 percent more than expected, and could rise 3 to 6.5 feet by the end of the century.
-Carbon dioxide emissions from fossil fuels in 2008 were about 40 percent higher than in 1990.

"This report shows that, contrary to the claims of `skeptics,' the scientific community actually underestimated both the magnitude and the rate of global climate change," said Edward Miles, a UW professor of marine affairs and director of the Pacific Northwest Climate Impacts Group at the UW.

"In addition, since 2005 the growth in fossil fuel emissions exceeds the worst-case scenarios of the Intergovernmental Panel on Climate Change, demonstrating clearly that world population growth and increasing demands for fossil fuels from the developing world are now a major driver of climate change," said Miles, who was not involved in preparing "The Copenhagen Diagnosis."

"These trends raise serious questions about our ability to manage changing rates and magnitudes of change in the future and increasingly severe questions about environmental security."

The "Copenhagen Diagnosis" noted that even if emissions do not increase beyond today's levels, in 20 years there still would be a one-in-four chance that the world cannot limit warming to less than 2 degrees Celsius, or 3.6 degrees Fahrenheit.

The report's 26 authors come from eight different countries, with six from the United States. Most of the collaborating scientists are authors of previous reports for the Intergovernmental Panel on Climate Change, which was established in 1988 by the United Nations and the World Meteorological Organization and which shared the 2007 Nobel Peace Prize.

University of Washington


0 comentarios

Scientists have revealed how environmental irritants such as air pollution and cigarette smoke cause people to cough, in research published in the American Journal of Respiratory and Critical Care Medicine. The authors of the study, from Imperial College London and the University of Hull, have identified the reaction inside the lungs that can trigger coughing when a person is exposed to particular irritants in the air. They suggest that their findings may ultimately lead to the development of new treatments for chronic coughing.

Coughing is the most common reason for people visiting a family doctor. Treatment options are limited for people with chronic coughing; a recent study concluded that over-the-counter remedies are ineffective and there is increasing concern about the safety of these therapies in children.

The study indicates, for the first time, how coughing can be triggered when a person is exposed to certain irritants in the air. It shows that the irritants can switch on receptor proteins called TRPA1 on the surface of nerve endings in the lungs. This switches on sensory nerves, which then trigger a cough reflex. The researchers say coughing could potentially be treated by blocking TRPA1 receptors, to stop irritants in the air from setting off this chain reaction. They hope that this could ultimately help millions of people whose lives are affected by chronic coughing.

Professor Maria Belvisi, corresponding author of the study from the National Heart and Lung Institute at Imperial College London, said: "For some people, chronic coughing can be annoying and uncomfortable, but for others it can be distressing and can have a severe impact on their quality of life. Many people say that certain things in the air can make them cough and we are very excited that we have shown, for the first time, exactly what is probably happening inside the lungs. Now that we think we have cracked the mechanism, we can start investigating whether we can stop people from coughing excessively by blocking the receptor protein that triggers it."

To reach their conclusions, the researchers first looked at sensory nerves from mice, guinea pigs and humans, and showed that the receptors on the sensory nerves were activated by a number of irritants, including a key compound in cigarette smoke (acrolein) and a chemical called cinnamaldehyde. The researchers then blocked the receptors and showed that these substances no longer activated the nerves.

To establish whether activating the receptor causes coughing, the researchers looked at the effect of acrolein on guinea pigs, as they have a coughing reflex. The researchers assessed the guinea pigs' coughing after inhaling acrolein. The compound caused coughing, and the higher the concentration, the more the guinea pigs coughed. The researchers then showed that blocking the receptor using a drug significantly reduced the guinea pigs' coughing response to the compound.

Finally, researchers led by Professor Alyn Morice at the University of Hull looked at the effect of inhaling the chemical cinnamaldehyde in humans. Ten healthy, non- smoking volunteers inhaled the chemical, as well as control substances. The researchers measured their cough response on five occasions, 2-3 days apart. All of the volunteers coughed after inhaling the compound.

(Photo: ICL)

Imperial College London


0 comentarios

Two teams of astronomers have found a planet outside the solar system that might be orbiting backwards compared to its star’s rotation, a discovery that could shed light on how unique the relatively perfect alignment of our solar system is compared to that of other planetary systems.

By measuring the rotation of the parent star of HAT-P-7b, a planet discovered in 2008, the two teams, including one led by MIT assistant professor of physics Joshua Winn and the other by Norio Narita at the National Astronomical Observatory of Japan, found that the orbit is tilted by at least 86 degrees with respect to the star’s equator. The drastic misalignment of the exoplanet, or planet outside our solar system, suggests that it is either rotating over both poles of its star or actually rotating backwards, a phenomenon that does not occur in our solar system and that could help explain why life thrives here.

More than 400 exoplanets have been discovered since 1995 thanks to large ground-based telescopes that have made it easier to observe such planets. Their study is important because their diverse orbits provide evidence that can help astronomers better understand how planets form.

The popularity of studying exoplanets has revived stellar astronomy, the study of how stars form, which had taken a backseat to other fields like cosmology until recently, according to Adam Burrows, an astrophysicist at Princeton University. But “in order to understand the planets, we need to understand the stars,” Burrows explained, noting that many planet properties evolved in terms of stellar parameters like masses, radii and spectra. Because planet formation is understood in the context of star formation, planetary and stellar astronomy “need each other,” Burrows said.

The planets in our solar system are well-aligned and prograde, revolving in the same direction as that of their parent star, the sun. For hundreds of years, astronomers have considered this pattern as a clue that the planets and sun formed from the same spinning disk of gas and dust. They have assumed the same about other planetary systems, Winn said.

But recent developments in exoplanetary science suggest that exoplanets do not conform to previous theories of orbital evolution and may have developed in a manner entirely different from that of the solar system.

The study of exoplanets provides the context for understanding how unusual, or perhaps normal, the solar system is. That there’s life in our solar system could have something to do with the fact that its planets are aligned nearly perfectly with the sun. Or perhaps this orderly alignment of planets is the norm, and it is the tilted exoplanet systems that are “the weird oddballs,” Winn explained.

The HAT-P-7b discovery is not the first exoplanet found to have a tilted orbit. In February, Winn’s team found another exoplanet with a tilt of 37 degrees. But his latest discovery is “by far the most drastic case of a misalignment” ever found, according to Winn, whose research was published in a paper in the Astrophysical Journal in October.

In addition to Winn and Simon Albrecht, a postdoctoral fellow in Winn’s group at MIT, the team included John Asher Johnson of the University of Hawaii; Andrew Howard and Geoffrey Marcy of the University of California, Berkeley; Ian Crossfield of the University of California, Los Angeles; and Matthew Holman of the Harvard-Smithsonian Center for Astrophysics. The work was funded by the NASA Origins program.

Winn’s team discovered the misalignment in July using the Japanese Subaru telescope in Hawaii. To measure the angle of orbit of HAT-P-7b, which is 1.4 times as wide and 1.8 times as massive as Jupiter and located about 1,000 light years away, it was necessary that it be an “eclipsing” planet, or one that passes in front of its sun from our perspective.

“There are only about 60 eclipsing exoplanets known, and we’ve just been making our way down the list,” said Albrecht. HAT-P-7b is the 15th exoplanet measured by Winn and his colleagues as it eclipses.

The eclipsing exoplanet allows astronomers to rely on the Doppler shift phenomenon that creates subtle color changes measured by a high resolution spectograph when something moves, such as a rotating star. When something moves toward us, it looks slightly bluer, and when it moves away from us, it looks slightly redder, Winn explained.

If an exoplanet’s orbit happens to be viewed from just the right angle, so that the planet passes directly in front of the star once per orbit, then the planet blocks a small fraction of the starlight from reaching Earth. This not only causes the star to appear dimmer, but also changes the spectrum of the star, which is the rainbow of colors you see when light passes through a prism. According to Winn, if a planet is prograde, it first passes in front of the approaching or blue half of the star, and this causes a red shift in the observed starlight. The planet then passes over the receding or red half of the star, causing a blue shift.

Winn’s team observed the opposite pattern for HAT-P-7b. “First, we saw the starlight get bluer, and then redder,” Albrecht said. “In all the other cases we’ve looked at, the light got redder and then bluer. This told us that from our vantage point on Earth, the HAT-P-7b star seems to rotate in the opposite direction as the revolution of its planet.”

By measuring these changes, one can estimate the angle between the star’s axis and the planet’s orbit. Winn’s team estimates that angle is anywhere between at least 86 and 180 degrees. This means the exoplanet is either orbiting its star’s poles at about a 90 degree tilt, or it is rotating backwards along the star’s equator at 180 degrees.

“There is a large range of uncertainty because we have not measured the true angle between the orbit and the stellar equator. Instead we can only measure the angle that we see from our perspective on Earth,” Winn explained. What remains unknown is how tilted the stellar rotation axis is with respect to our line of sight.

The Japanese team reported similar results in a paper published in the Publications of Astronomical Society of Japan Letters in October.

Because theorists are reluctant to abandon the theory that all planets and their stars form from a disk of the same material, they are focusing on the notion that the exoplanets formed in a “normal” orbit and somehow got tipped over, according to Winn.

One possibility is that multiple planets formed in what turned out to be an unstable configuration, with their gravity scrambling each other’s orbits to some degree, giving way to “something more chaotic with planets going every which way,” Winn said.

Or perhaps there is a third object, such as an additional planet or a companion star, in the system whose gravity perturbs the orbit of the exoplanet and tilts it, a phenomenon known as the Kozai effect.

“The goal is to figure out how frequently this happens to determine how unlikely our little corner of the galaxy may be,” Winn said. In August, a European team announced it had discovered a retrograde exoplanet known as WASP-17b, although the team’s findings have not yet been published.

Adam Burrows predicts that HAT-P-7b will be highly scrutinized because it is one of the few exoplanets that can be seen by the NASA satellite Kepler and could help break open the field of stellar astronomy.

“Years ago the field was in the doldrums,” Burrows explained. “But now, because of these findings, the field is coming into its own again. There is a renaissance, and this is in no small measure because of observers like Josh who have galvanized the subject.”

(Photo: Simon Albrecht)


0 comentarios

A new study provides “incontrovertible evidence” that the volcanic super-eruption of Toba on the island of Sumatra about 73,000 years ago deforested much of central India, some 3,000 miles from the epicenter, researchers report.

The volcano ejected an estimated 800 cubic kilometers of ash into the atmosphere, leaving a crater (now the world’s largest volcanic lake) that is 100 kilometers long and 35 kilometers wide. Ash from the event has been found in India, the Indian Ocean, the Bay of Bengal and the South China Sea.

The bright ash reflected sunlight off the landscape, and volcanic sulfur aerosols impeded solar radiation for six years, initiating an “Instant Ice Age” that – according to evidence in ice cores taken in Greenland – lasted about 1,800 years.

During this instant ice age, temperatures dropped by as much as 16 degrees centigrade (28 degrees Fahrenheit), said University of Illinois anthropology professor Stanley Ambrose, a principal investigator on the new study with professor Martin A.J. Williams, of the University of Adelaide. Williams, who discovered a layer of Toba ash in central India in 1980, led the research.

The climactic effects of Toba have been a source of controversy for years, and its impact on human populations is also hotly debated.

In 1998, Ambrose proposed in the Journal of Human Evolution that the effects of the Toba eruption and the Ice Age that followed could explain the apparent bottleneck in human populations that geneticists believe occurred between 50,000 and 100,000 years ago. The lack of genetic diversity among humans alive today suggests that during this time period humans came very close to becoming extinct.

To address the limited evidence of the terrestrial effects of Toba, Ambrose and his colleagues pursued two lines of inquiry: They analyzed pollen from a marine core in the Bay of Bengal that included a layer of ash from the Toba eruption, and they looked at carbon isotope ratios in fossil soil carbonates taken from directly above and below the Toba ash in three locations in central India. Carbon isotopes reflect the type of vegetation that existed at a given locale and time.

Heavily forested regions leave carbon isotope fingerprints that are distinct from those of grasses or grassy woodlands.

Both lines of evidence revealed a distinct change in the type of vegetation in India immediately after the Toba eruption, the researchers report. The pollen analysis indicated a shift to a “more open vegetation cover and reduced representation of ferns, particularly in the first 5 to 7 centimeters above the Toba ash,” they wrote in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. The change in vegetation and the loss of ferns, which grow best in humid conditions, they wrote, “would suggest significantly drier conditions in this region for at least one thousand years after the Toba eruption.”

The dryness probably also indicates a drop in temperature, Ambrose said, “because when you turn down the temperature you also turn down the rainfall.”

The carbon isotope analysis was even more explicit. It showed that forests covered central India when the eruption occurred, but wooded to open grassland predominated for at least 1,000 years after the eruption.

“This is unambiguous evidence that Toba caused deforestation in the tropics for a long time,” Ambrose said. This disaster may have forced the ancestors of modern humans to adopt new cooperative strategies for survival that eventually permitted them to replace neandertals and other archaic human species, he said.

(Photo: L. Brian Stauffer)

University of Illinois




Selected Science News. Copyright 2008 All Rights Reserved Revolution Two Church theme by Brian Gardner Converted into Blogger Template by Bloganol dot com