Tuesday, March 23, 2010

UM STUDY LAYS GROUNDWORK FOR NEW, NON-INVASIVE BRAIN-COMPUTER INTERFACE TECHNOLOGY

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New findings by a team of University of Maryland researchers may lead to new, non-invasive technologies for portable brain-computer interface systems. Such technologies potentially could allow people with disabilities or paralysis to operate a robotic arm, motorized wheelchair or other prosthetic device using a headset with scalp sensors that send signals from the brain to the device.

Led by Maryland's Jose Contreras-Vidal, an associate professor of kinesiology, the team of neuroscientists successfully reconstructed 3-D hand motions from brain signals recorded in a non-invasive way. Their results are published in the March 3 issue of The Journal of Neuroscience. In this study the scientists placed an array of 34 sensors on the scalps of five participants to record their brains' electrical activity, using a process called electroencephalography, or EEG.

Volunteers were asked to reach from a center button and touch eight other buttons in random order 10 times, while the authors recorded their brain signals and hand motions. Afterward, the researchers attempted to decode the signals and reconstruct the 3-D hand movements.

"Our results showed that electrical brain activity acquired from the scalp surface carries enough information to reconstruct continuous, unconstrained hand movements," said Contreras- Vidal, who also holds appointments in bioengineering, the university's Neuroscience and Cognitive Science Program and its Center on Aging.

"Our ground-breaking research opens the possibility for the development of assistive devices for the neurologically-impaired or disabled. We are currently working with robotic arms and wearable upper limb exoskeletons [as shown in above image], but there are a number of steps before this technology can be applied clinically," said Contreras-Vidal.

Prior to this study, researchers have used non-portable and invasive methods that place sensors inside the brain when reconstructing hand motions.

Vidal, with Maryland colleagues Trent Bradberry, a graduate student in the Fischell Department of Bioengineering and Rodolphe Gentili, a research assistant professor of kinesiology, found that one sensor in particular provided the most accurate information. The sensor was located over a part of the brain called the primary sensorimotor cortex, a region associated with voluntary movement. Useful signals were also recorded from another region called the inferior parietal lobule, which is known to help guide limb movement. The authors used these findings to confirm the validity of their methods.

A release from the Society for Neuroscience said this study has implications for future brain-computer interface technologies and for those already in existence. An expert unaffiliated with the study, Jonathan Wolpaw, MD, of the New York State Department of Health's Wadsworth Center in Albany, was quoted. "It may eventually be possible for people with severe neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS), stroke, or spinal cord injury, to regain control of complex tasks without needing to have electrodes implanted in their brains. [This] paper enhances the potential value of EEG for laboratory studies and clinical monitoring of brain function," said Wolpaw.

The findings also could lead to improvements in existing EEG-based systems that are designed to allow movement-impaired people to control a computer cursor with their thoughts. Such systems now require that users undergo extensive training. However, according to Contreras-Vidal more effortless control could be achieved with such systems and the length of training required to use them could be reduced using the methods in this study.

(Photo: U. Maryland)

University of Maryland

RESEARCHERS SHOW HOW FAR SOUTH AMERICAN CITIES MOVED IN QUAKE

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The massive magnitude 8.8 earthquake that struck the west coast of Chile last month moved the entire city of Concepcion at least 10 feet to the west, and shifted other parts of South America as far apart as the Falkland Islands and Fortaleza, Brazil.

These preliminary measurements, produced from data gathered by researchers from four universities and several agencies, including geophysicists on the ground in Chile, paint a much clearer picture of the power behind this temblor, believed to be the fifth-most-powerful since instruments have been available to measure seismic shifts.

Buenos Aires, the capital of Argentina and across the continent from the quake’s epicenter, moved about 1 inch to the west. And Chile’s capital, Santiago, moved about 11 inches to the west-southwest. The cities of Valparaiso and Mendoza, Argentina, northeast of Concepcion, also moved significantly.

The quake’s epicenter was in a region of South America that’s part of the so-called “ring of fire,” an area of major seismic stresses which encircles the Pacific Ocean. All along this line, the tectonic plates on which the continents move press against each other at fault zones.

The February Chilean quake occurred where the Nazca tectonic plate was squeezed under, or “subducted,” below the adjacent South American plate. Quakes routinely relieve pent-up geologic pressures in these convergence zones.

The research team deduced the cities’ movement by comparing precise GPS (global positioning satellite) locations known prior to the major quake to those almost 10 days later. The US Geological Survey reported that there have been dozens of aftershocks, many exceeding magnitude 6.0 or greater, since the initial event February 27.

Mike Bevis, professor of earth sciences at Ohio State University, has led a project since 1993 that has been measuring crustal motion and deformation in the Central and Southern Andes. The effort, called the Central and Southern Andes GPS Project, or CAP, hopes to perhaps triple its current network of 25 GPS stations spread across the region.

"By reoccupying the existing GPS stations, CAP can determine the displacements, or 'jumps', that occurred during the earthquake," Bevis said. “By building new stations, the project can monitor the postseismic deformations that are expected to occur for many years, giving us new insights into the physics of the earthquake process.”

Ben Brooks, an associate researcher with the School of Ocean and Earth Science and Technology at the University of Hawaii and co-principal investigator on the project, said that the event, tragic as it was, offers a unique opportunity to better understand the seismic processes that control earthquakes.

“The Maule earthquake will arguably become one of the, if not the most important great earthquake yet studied. We now have modern, precise instruments to evaluate this event, and because the site abuts a continent, we will be able to obtain dense spatial sampling of the changes it caused.

“As such the event represents an unprecedented opportunity for the earth science community if certain observations are made with quickly and comprehensively,” Brooks said.

(Photo: OSU)

Ohio State University

FIRST MEASUREMENT OF THE AGE OF COMETARY MATERIAL

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Though comets are thought to be some of the oldest, most primitive bodies in the solar system, new research on comet Wild 2 indicates that inner solar system material was transported to the comet-forming region at least 1.7 million years after the formation of the oldest solar system solids.

The research by Lawrence Livermore National Laboratory scientists and colleagues provides the first constraint on the age of cometary material from a known comet. The findings are published in the Feb. 25 edition of Science Express.

The NASA Stardust mission to comet Wild 2, which launched in 1999, was designed around the premise that comets preserve pristine remnants of materials that helped form the solar system. In 2006, Stardust returned with the first samples from a comet.

Though the mission was expected to provide a unique glimpse into the early solar system by returning a mix of solar system condensates, amorphous grains from the interstellar medium and true stardust (crystalline grains originating in distant stars), the initial results painted a different picture. Instead, the comet materials consisted of high-temperature materials including calcium-aluminum rich inclusions (CAIs), the oldest objects formed in the solar nebula. These objects form in the inner regions of the solar nebula and are common in meteorites.

The presence of CAIs in comet Wild 2 indicates that the formation of the solar system included mixing over radial distances much greater than has been recognized by scientists in the past.

“The inner solar system material in Wild 2 underscores the importance of radial transport of material over large distances in the early solar nebula,” said lead author Jennifer Matzel of the Laboratory‘s Institute of Geophysics and Planetary Science and the Glenn T. Seaborg Institute. “These findings also raise key questions regarding the timescale of the formation of comets and the relationship between Wild 2 and other primitive solar nebula objects.” Analysis showed that the inner solar system materials formed 1.7 million years after the onset of CAI formation.

(Photo: LLNL)

Lawrence Livermore National Laboratory

GAME ON? VIDEO-GAME OWNERSHIP MAY INTERFERE WITH YOUNG BOYS' ACADEMIC FUNCTIONING

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Parents of young boys may want to encourage moderation when it comes to their kids' video game habits. According to new findings in Psychological Science, a journal of the Association for Psychological Science, owning a video-game system may hamper academic development in some children.

Psychological scientists Robert Weis and Brittany C. Cerankosky of Denison University conducted a study examining short-term effects of video-game ownership on academic development in young boys. Families with boys between the ages of 6 to 9 were recruited for this study. The families did not own video-game systems, but the parents had been considering buying one for their kids. The children completed intelligence tests as well as reading and writing assessments. In addition, the boys' parents and teachers filled out questionnaires relating to their behavior at home and at school. Half of the families were selected to receive a video-game system (along with three, age-appropriate video games) immediately, while the remaining families were promised a video-game system four months later, at the end of the experiment. Over the course of the four months, the parents recorded their children's activities from the end of the school day until bedtime. At the four-month time point, the children repeated the reading and writing assessments and parents and teachers again completed the behavioral questionnaires.

The results of this study showed that the boys who received the video-game system immediately spent more time playing video games and less time engaged in after-school academic activities than boys who received the video-game system at the end of the experiment. Furthermore, the boys who received the video-game system at the beginning of the study had significantly lower reading and writing scores four months later compared with the boys receiving the video-game system later on. Although there were no differences in parent-reported behavioral problems between the two groups of kids, the boys who received the video-game system immediately had greater teacher-reported learning problems.

Further analysis revealed that the time spent playing video games may link the relationship between owning a video-game system and reading and writing scores. These findings suggest that video games may be displacing after-school academic activities and may impede reading and writing development in young boys. The authors note that when children have problems with language at this young age, they tend to have a tougher time acquiring advanced reading and writing skills later on. They conclude, "Altogether, our findings suggest that video-game ownership may impair academic achievement for some boys in a manner that has real-world significance."

Psychological Science

STUDENTS' PERCEPTIONS OF EARTH'S AGE INFLUENCE ACCEPTANCE OF HUMAN EVOLUTION

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High school and college students who understand the geological age of the Earth (4.5 billion years) are much more likely to understand and accept human evolution, according to a University of Minnesota study published in the March issue of the journal Evolution.

The finding could give educators a new strategy for teaching evolution, since the Earth's age is typically covered in physical rather than biological science classes.

Researchers Sehoya Cotner and Randy Moore, professors in College of Biological Sciences, and D. Christopher Brooks, of the university's Office of Information Technology, surveyed 400 students enrolled in several sections of a University of Minnesota introductory biology course for non-majors.

The survey included questions about knowledge of evolution and whether students were taught evolution or creationism in high school as well as questions about religious and political views. Participation was voluntary and had no effect on grades for the course.

The researchers extracted six variables from the survey to explore factors that contributed to students' views about the age of the Earth and origins of life and the relation of those beliefs to students' knowledge of evolution and their vote in the 2008 presidential election.

Using that information, they created a model that shows, for example, when a student's religious and political views are liberal, they are more likely to believe that the Earth is billions, rather than thousands, of years old and to know more about evolution. Conversely, students with conservative religious and political views are more inclined to think the Earth is much younger (20,000 years or less) and to know less about evolution.

"The role of the Earth's age is a key variable that we can use to improve education about evolution, which is important because it is the unifying principle of biology," said lead author Sehoya Cotner, associate professor in the Biology Program, which provides general biology classes for University of Minnesota undergraduates.

Through this and previous surveys, Cotner and her colleagues have learned that 2 percent of students are taught creationism only, 22 percent are taught evolution and creationism, 14 are taught neither and 62 percent evolution only.

"In other words, about one in four high school biology teachers in the upper Midwest are giving students the impression that creationism is a viable explanation for the origins of life on Earth," Cotner says. "That's just not acceptable. The Constitution prohibits teaching creationism in schools."

The researchers noted that understanding the Earth's age is a difficult concept; even Darwin found it challenging. Teaching and understanding creationist views of about the Earth's age and life's origins are much easier.

The paper cites a 2009 Gallup poll that coincided with the 200th anniversary of Darwin's birth reporting that only four out of 10 people in the U.S. believe in evolution. The poll also reported that 16 percent of biology teachers believe God created humans in their present form at some time during the last 10,000 years.

University of Minnesota

PREHISTORIC RESPONSE TO GLOBAL WARMING INFORMS HUMAN PLANNING TODAY

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Since 2004, University at Buffalo anthropologist Ezra Zubrow has worked intensively with teams of scientists in the Arctic regions of St. James Bay, Quebec, northern Finland and Kamchatka to understand how humans living 4,000 to 6,000 years ago reacted to climate changes.

"The circumpolar north is widely seen as an observatory for changing relations between human societies and their environment," Zubrow explains, "and analysis of data gathered from all phases of the study eventually will enable more effective collaboration between today's social, natural and medical sciences as they begin to devise adequate responses to the global warming the world faces today."

This study, which will collect a vast array of archaeological and paleoenvironmental data, began with the Social Change and the Environment in Nordic Prehistory Project (SCENOP), a major international research study by scientists from the U.S., Canada and Europe of prehistoric sites in Northern Quebec and Finland.

Phases I and II of the study were headed by André Costopoulos and Gail Chmura of McGill University (Montreal), Jari Okkonen of Finland's Oulu University, and Zubrow, who directs UB's Social Systems Geographic Information Systems Lab.

Phase III, underway now, is the International Circumpolar Archaeological Project (ICAP) funded by $845,796 from the National Science Foundation's Arctic Social Sciences Program of the Office of Polar Programs, which is supported by the American Recovery and Reinvestment Act (ARRA). Headed by Zubrow, it focuses on a third sub-arctic region: Siberia's remote Kamchatka peninsula, a rough and extremely volcanic wilderness region the size of California.

"With forecasts of sea-level rises and changing weather patterns, people today have been forewarned about some likely ramifications of climate change," Zubrow says, "but those living thousands of years ago, during the Holocene climatic optimum, could not have known what lay ahead of them and how their land -- and lives -- would be changing.

"This was a slower change," he says, "about one-third the rate we face today. In the Holocene period, it took a thousand years for the earth to warm as much as it has over the past 300 years -- roughly the time spanned since the beginning of the Industrial Revolution.

"As in other phases of the study," Zubrow says, "our goal in Kamchatka is to clarify ancient regional chronologies and understand the ways prehistoric humans adapted to significant environmental changes, including warming, earthquakes, tsunamis, volcanic eruptions and the seismic uplift of marine terraces that impacted the environment during the period in question."

He points out that, despite our more sophisticated prediction technology, and technologies overall, many of the world's people have residences and lifestyles that are just as vulnerable to climatic shift as those of our prehistoric ancestors. They, too, live along estuaries and coastlines subject to marked alteration as oceans rise.

Most of the ARRA stimulus money used in the project is spent in the United States on salaries and research at various universities. Zubrow reiterates a point he often makes with his students: "This research funding is good for science, good for the economy, good for the government and good for the international reputation of the United States."

Ultimately, information gathered over the next year by the geologists, archaeologists, geochemists, volcanologists and paleoecologists on Zubrow's team will be compared with data from the two other ICAP sites.

During an additional study phase funded by a $300,000 grant from NSF, through the ARRA, Zubrow will conduct archaeological research in Mexico to ascertain how arctic climatic changes during the mid- and post-Holocene era affected human populations in a changing temperate climate.

(Photo: U. Barcelona)

University at Buffalo

CATASTROPHIC EVENT BEHIND THE HALT OF STAR BIRTH IN EARLY GALAXY FORMATION

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Scientists have found evidence of a catastrophic event they believe was responsible for halting the birth of stars in a galaxy in the early Universe. They report their results in the journal Monthly Notices of the Royal Astronomical Society.

The researchers, led by Durham University’s Department of Physics and funded by the Royal Society and Royal Astronomical Society say the massive galaxy, SMM J1237+6203, underwent a series of blasts trillions of times more powerful than any caused by an atomic bomb. The blasts happened every second for millions of years, according to the scientists.

The explosions scattered the gas needed to form new stars by helping it escape the gravitational pull of the galaxy, effectively regulating its development. The Durham-led team believes the huge surge of energy was caused by either the outflow of debris from the galaxy’s black hole or from powerful winds generated by dying stars exploding as supernovae.

SMM J1237+6203 lies in the direction of the constellation Ursa Major and is so far away that we see it as it appeared 10 billion years ago, or three billion years after the Big Bang, when the Universe was only one quarter of its present age.

Properties seen in massive galaxies nearer to our own galaxy, the Milky Way, suggest that a major event rapidly turned off star formation in galaxies early in the history of the Universe and stopped them from expanding. Theorists, including scientists at Durham University, have argued that this could be due to outflows of energy blowing galaxies apart and preventing further new stars from forming, but until now evidence for this has been lacking.

Using the Gemini Near-Infrared Integral Field Spectrometer (NIFS) to measure the speed of material in the galaxy, they found huge outflows powerful enough to help star-forming debris escape the galaxy’s gravitational pull. They believe the colossal energies generated by these outflows of energy were enough to suppress any further star formation in the galaxy.

Dr Dave Alexander, of Durham University’s Department of Physics, said: “We are looking into the past and seeing a catastrophic event that essentially switched off star formation and halted the growth of a typical massive galaxy in the early Universe.

‘Effectively the galaxy is regulating its growth by preventing new stars from being born. Theorists had predicted that huge outflows of energy were behind this activity, but it’s only now that we have seen it in action.

‘We believe that similar huge outflows are likely to have stopped the growth of other galaxies in the early Universe by blowing away the materials needed for star formation.”

The Durham-led team now plans to study other massive forming galaxies in the early Universe to see if they display similar characteristics.

(Photo: NASA/CXC/M.Weiss)

Royal Astronomical Society

GENOME SEQUENCED FOR AMOEBA THAT FLIPS INTO FREE-SWIMMING CELL

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In the long evolutionary road from bacteria to humans, a major milestone occurred some 1.5 billion years ago when microbes started building closets for all their stuff, storing DNA inside a nucleus, for example, or cramming all the energy machinery inside mitochondria.

Scientists have now sequenced the genome of a weird, single-celled organism called Naegleria gruberi that is telling biologists about that transition from prokaryotes, which function just fine with all their proteins floating around in a soup, to eukaryotes, which neatly compartmentalize those proteins.

The sequence, produced by the Department of Energy Joint Genome Institute (JGI), and an analysis by scientists from the University of California, Berkeley, Lancaster University in the United Kingdom and institutions elsewhere in the United States and the U.K. are published in the March 5 issue of the journal Cell.

"In a sense, analyzing the Naegleria genome shows us what it would be like to be on this planet more than a billion years ago, and what kind of organisms were around then and what they might have looked like," said Simon E. Prochnik, a JGI and UC Berkeley bioinformaticist and coauthor of the Cell paper.

Naegleria is a common soil amoeba - the sequenced organism was isolated from the mud in a grove of eucalyptus trees on the UC Berkeley campus - that, under stress, quickly grows two flagella, like sperm tails, that it uses to swim around. It has a third identity, a hard cyst, that can persist in the soil until conditions become damp and warm enough for it to turn into an amoeba.

"This one-celled organism hunts and eats bacteria as an amoeba, swims around looking for a better environment as a flagellate, and then hunkers down and waits for good times as a cyst," Prochnik said. "It is a very rare process to go from amoeba to flagellate like this."

Not surprisingly, the organism is packed with genes that help support these three personalities, he said. He and his colleagues report that this amoeboflagellate contains 15,727 genes coding for proteins, while humans have 23,000 protein-coding genes.

"Naegleria has a lot of genes because it has a complicated lifestyle; most single-celled organisms - in particular, parasites - have a simpler lifestyle, and therefore have fewer genes," Prochnik said. "These single-celled organisms are highly versatile, containing all the genetic information necessary to survive in a wide range of environments and under a wide range of stresses."

The researchers compared the Naegleria genome to the genomes of 16 other eukaryotes, ranging from humans and fungi to green plants and other unicellular eukaryotes, shedding light on the set of perhaps 4,000 genes that may have been part of the first, most primitive eukaryotes, according to UC Berkeley graduate student Lillian Fritz-Laylin, first author of the paper. The number of genes surprised the researchers, because previous genome comparisons that included parasites came up with a much lower number. That may be because parasites live off their host and have been able to shed many genes that are critical for a free-living organism, they said.

"Now that our analysis focuses on data from free-living organisms, including Naegleria, that haven't lost all these genes and functions, we can make a broader comparison, and we find a lot more proteins were probably present in the eukaryotic ancestor than we previously thought," Fritz-Laylin said.

"This is the first genome comparison that includes not only Naegleria, but representatives of all six sequenced groups of eukaryotes," Prochnik said. Naegleria is part of a diverse group that includes a cousin, Naegleria fowleri, that can fatally infect swimmers. The other eurkaryotic groups are animals and fungi; plants and green algae; chromalveolata, which include diatoms, red tide and malaria; amoebozoa, which include various single-celled amoebae; and the diverse group that includes parasites like giardia.

Among other things, Naegleria's genes shed light on how cells move, how they signal one another and how they metabolize nutrients.

As an amoeba, Naegleria pushes out little feet, called pseudopods, that propel it in its hunt for food. Yet, once the food disappears, the amoeba creates flagella from scratch and uses them to swim about in search of new hunting grounds.

What is interesting, Fritz-Laylin said, is that pseudopods and flagella use different proteins for movement. Amoebae make use of actin, which provides the internal scaffolding for the cell and for the pseudopods that help amoebae explore their environment. Flagella, on the other hand, are made mostly of the protein tubulin. Because Naegleria has both types of movement, the organism can help scientists understand the origins of these parallel systems during the evolution of eukaryotes.

Scientists can starve populations of Naegleria in its amoeba form and have seen it switch quickly and simultaneously to its flagellar form. This suggests that the switch from an actin-based system to a microtubule-based system of movement is very highly regulated and synchronized across a population.

"The sequence helped us identify the genes associated with each type of motility," she said. "Although this has been done for flagellar motility, it had not been done for amoeboid motility."

The genome also reveals versatility in how Naegleria produces energy. The organism can use oxygen to burn nutrients - glucose, amino acids or fatty acids - for energy or, in the absence of oxygen, utilize other nutrients and possibly produce hydrogen as a byproduct.

Like the recently sequenced, free-living alga Chlamydomonas, Naegleria likely uses its metabolic flexibility to survive the intermittent hypoxia common to muddy environments, the researchers concluded. Prochnik suggests that Naegleria could help biologists understand hydrogen production that, in other organisms, might be used to produce energy.

Fritz-Laylin noted that, while the genome will be a boon to the small number of biologists who study the organism, it also will help in understanding the evolution of more complicated organisms.

"By comparing diverse organisms like Naegleria from all over the family tree of eukaryotes we can begin to understand where we come from," she said.

(Photo: Lillian Fritz-Laylin/UC Berkeley)

University of California, Berkeley

OLDEST MEASUREMENT OF EARTH'S MAGNETIC FIELD REVEALS HISTORY OF BATTLE BETWEEN SUN AND EARTH FOR OUR ATMOSPHERE

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Scientists at the University of Rochester have discovered that the Earth's magnetic field 3.5 billion years ago was only half as strong as it is today, and that this weakness, coupled with a strong wind of energetic particles from the young Sun, likely stripped water from the early Earth's atmosphere.

The findings, presented in Science, suggest that the magnetopause—the boundary where the Earth's magnetic field successfully deflects the Sun's incoming solar wind—was only half the distance from Earth it is today.

"With a weak magnetosphere and a rapid-rotating young Sun, the Earth was likely receiving as many solar protons on an average day as we get today during a severe solar storm," says John Tarduno, a geophysicist at the University of Rochester and lead author of the study. "That means the particles streaming out of the Sun were much more likely to reach Earth. It's very likely the solar wind was removing volatile molecules, like hydrogen, from the atmosphere at a much greater rate than we're losing them today." Tarduno says the loss of hydrogen implies a loss of water as well, meaning there may be much less water on Earth today than in its infancy.

To find the strength of the ancient magnetic field, Tarduno and his colleagues from the University of KwaZulu-Natal visited sites in Africa that were known to contain rocks in excess of 3 billion years of age. Not just any rocks of that age would do, however. Certain igneous rocks called dacites contain small millimeter-sized quartz crystals, which in turn have tiny nanometer-sized magnetic inclusions. The magnetization of these inclusions act as minute compasses, locking in a record of the Earth's magnetic field as the dacite cooled from molten magma to hard rock. Simply finding rocks of this age is difficult enough, but such rocks have also witnessed billions of years of geological activity that could have reheated them and possibly changed their initial magnetic record. To reduce the chance of this contamination, Tarduno picked out the best preserved grains of quartz out of 3.5 billion-year-old dacite outcroppings in South Africa.

Complicating the search for the right rocks further, the effect of the solar wind interacting with the atmosphere can induce a magnetic field of its own, so even if Tarduno did find a rock that had not been altered in 3.5 billion years, he had to make sure the magnetic record it contained was generated by the Earth's core and not induced by the solar wind.

Once he isolated the ideal crystals, Tarduno used a device called a superconducting quantum interface device, or SQUID magnetometer, which is normally used to troubleshoot computer chips because it's extremely sensitive to the smallest magnetic fields. Tarduno pioneered the use of single crystal analyses using SQUID magnetometers. However, for this study, even standard SQUID magnetometers lacked the sensitivity. Tarduno was able to employ a new magnetometer, which has sensors closer to the sample than in previous instruments.

Using the new magnetometer, Tarduno, Research Scientist Rory Cottrell, and University of Rochester students were able to confirm that the 3.5 billion-year-old silicate crystals had recorded a field much too strong to be induced by the solar wind-atmosphere interaction, and so must have been generated by Earth's core.

"We gained a pretty solid idea of how strong Earth's field was at that time, but we knew that was only half the picture," says Tarduno. "We needed to understand how much solar wind that magnetic field was deflecting because that would tell us what was probably happening to Earth's atmosphere."

The solar wind can strip away a planet's atmosphere and bathe its surface in lethal radiation. Tarduno points to Mars as an example of a planet that likely lost its magnetosphere early in its history, letting the bombardment of solar wind slowly erode its atmosphere. To discover what kind of solar wind the Earth had to contend with, Tarduno employed the help of Eric Mamajek, assistant professor of physics and astronomy at the University of Rochester.

"There is a strong correlation between how old a Sun-like star is and the amount of matter it throws off as solar wind," says Mamajek "Judging from the rotation and activity we expect of our Sun at a billion years of age, we think that it was shedding material at a rate about 100 times stronger than the average rate observed in modern times."

While the life cycle of stars like our Sun is well known, says Mamajek, astrophysicists have only a handful of stars for which they know the amount of mass lost as solar wind. Mamajek says the amount of X-rays radiated from a star, regardless of its apparent brightness, can give a good estimate of how much material the star is radiating as solar wind. Through the Sun at this age was likely about 23% dimmer than it would appear to us today, it was giving off much more radiation as X-rays, and driving a much more powerful solar wind.

"We estimate the solar wind at that time was a couple of orders of magnitude stronger," says Mamajek. "With Earth's weaker magnetosphere, the standoff point between the two was probably less than five Earth radii. That's less than half of the distance of 10.7 radii it is today."

Tarduno says that in addition to the smaller magnetopause allowing the solar wind to strip away more water vapor from the early Earth, the skies might have been filled with more polar aurora. The Earth's magnetic field bends toward vertical at the poles and channels the solar wind toward the Earth's surface there. When the solar wind strikes the atmosphere, it releases photons that appear as shifting patterns of light at night.

With the weakened magnetosphere, the area where the solar wind is channeled toward the surface—an area called the magnetic polar cap—would have been three times larger than it is today, says Tarduno.

"On a normal night 3.5 billion years ago you'd probably see the aurora as far south as New York," says Tarduno.

(Photo: U. Rochester)

University of Rochester

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