Yangtze River’s Ancient Origins Revealed

The Yangtze River in China is 40 million years older than was previously thought, according to new research.

A study of minerals by a team led by Durham University reveals that the Yangtze River began to cut the Three Gorges area around 45 million years ago, making it much older than previously believed.

The Yangtze River, the third-longest river in the world, has played a central role in the development of Chinese culture, and the Three Gorges, which separate the Sichuan Basin in the west from the lowlands of central and eastern China to the east, have particular historical, cultural, and geomorphological significance.

Without the transport pathway created by the Three Gorges, south-western China -- including the rich agricultural area of Sichuan Province, known as China's 'rice bowl' -- would have remained cut off from the rest of the country by the otherwise inaccessible mountains that surround the region.

The new findings, published in Geology, show that sediments from the Three Gorges, previously analysed by researchers and dated as being only 1-2 million years old, must have been deposited long after the Three Gorges were cut.

The research team, led by Dr Alexander Densmore from the Institute of Hazard, Risk and Resilience, Durham University, determined the onset of incision in the Three Gorges by looking at the cooling of minerals in the granite that underlies the Three Gorges Dam at Sandouping in Hubei Province. The granite containing these apatite grains was cooled to lower temperatures as the river cut down through it.

Prior work on the origin of the Three Gorges has shown that the Yangtze River most likely began as a set of small, non-descript streams that drained both west and east, out of a range of low mountains in central China.

It was argued that the merger of these streams gave rise to the progressive development of a much larger, east-flowing river system that became the Yangtze River. Many scientists agreed that the most likely point of merger of the streams was in the Three Gorges area.

Dr Alex Densmore said: "The fact that erosion had removed all of the evidence of the old, pre-merger river courses made dating the river particularly difficult.

"Prior attempts to date the Three Gorges placed their age at only 1-2 million years but this was based on sediments found within the gorges. If this were the case, the river would have had to have been carved into the rocks very quickly, and this would have required extremely high incision rates.

"We used the number of damage trails in the mineral apatite to tell us when the rocks were cooled below a particular temperature and thus when gorge incision began."

The research team, which involved scientists from Durham, Chengdu and Victoria universities, and researchers in the UK and Germany, found that samples near the gorges showed that cooling began about 45 million years ago, whereas samples taken farther away from the river show no evidence of that cooling. Thus, the cooling must have been caused by gorge incision, rather than by more regional erosion, according to the scientists.

Dr Densmore added: "The Yangtze River is much older than previously thought and extremely high incision rates were not required to create the distinctive gorges. It formed slowly, over a much longer time-span."

The research, funded by the Swiss Federal Institute of Technology, also helped to explain a mysterious episode of erosion that affected the eastern part of the Tibetan Plateau. 45 million years ago, sediment shed from the rising Tibetan Plateau to the west was trapped in a large basin upstream of the future Three Gorges area.

Dr Densmore said: "As the Gorges were cut, they acted as like a plughole in a giant bathtub, allowing that sediment to be eroded and flushed down into the growing Yangtze River and out into the East China Sea, depositing the sediment in the lowland areas of eastern China."

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Journal Reference:

1. N. J. Richardson, A. L. Densmore, D. Seward, M. Wipf, L. Yong. Did incision of the Three Gorges begin in the Eocene? Geology, 2010; 38 (6): 551 DOI: 10.1130/G30527.1

Oil Spill Puts Commercially Significant Cold-Water Reefs in Peril

Thousands of barrels of oil are leaking out of the Deepwater Horizon site each day. The oil ascends from depths of approximately 1502 m. (4928 ft.), but not all of it reaches the sea surface. The stratified seawater of the Gulf of Mexico captures or slows the ascent of the oil, and the addition of dispersants near the oil source produces tiny droplets that float for a considerable time in the water column and may never reach the surface.

According to Drs. Gregor Eberli, Mark Grasmueck, and Ph.D. candidate Thiago Correa of the Marine Geology & Geophysics division of the University of Miami (UM), the oil that remains in suspension in the water column and creates plumes poses a serious risk for the planktonic and benthic (sea floor) life throughout the region, including the deep-sea reefs they study.

"The deep water communities within the Gulf of Mexico and in the Straits of Florida are well hidden from us, but they include many species of cold-water corals that live in water at depths of 600 -- 1500 m. (1969 -4921 ft.) in waters as cold as 3° Celsius (37.4°F)," said Eberli. "Unlike their more familiar shallow-water counterparts, these corals do not live in symbiosis with unicellular algae called zooxanthellae, but are animals that feed on organic matter floating through the water column. We know that most of the food consumed by the cold-water corals is produced in the surface waters and eventually sinks down to the corals."

The large plumes being created by the oil spill, some of which are reported to be several miles long, sit in the water column situated between this source of food and these deep-water corals. As organic material sinks through the water column it passes through the oil plumes and is contaminated by micron-sized oil droplets.

"It is most likely that the delicate cold-water corals are not able to digest these oil-laden food particles and will perish in large numbers," said Eberli. "We are especially concerned because the migrating oil plumes have the potential to destroy or greatly diminish these deep-sea coral communities as they are carried by the currents. These corals are important because they are the foundation of a diverse ecosystem that at last count includes over 1,300 marine species, according to Dr. Thomas Hourigan at NOAA."

There is also a danger that these plumes are carried by the Loop Current from the Gulf of Mexico to the Atlantic Ocean. Deep-sea coral ecosystems are common at numerous sites from the eastern Gulf of Mexico through the Straits of Florida and northward to the Blake Plateau off North Carolina. This distribution matches the path of the Loop Current that forms from the water masses in the Gulf of Mexico, and enters the Straits of Florida to form the Florida Current and further north the Gulf Stream.

Particularly vulnerable to disturbance are deep-sea fish that form part of this ecosystem because of their late maturation, extreme longevity, low fecundity and slow growth. Deep-water coral reefs in Florida waters are the habitat of the economically valuable grouper, snapper and amberjack. These and other species inhabit hundreds of deep-water coral reefs off the coast of Florida at depths of about 300 -915 m. (1000 to 3000 feet), which were explored by Dr. John Reed from Harbor Branch Oceanographic Institute some thirty years ago. This includes the 59,500 sq. m. (~23,000 sq. mi.) of deep-water reefs off the east coast of Florida, which is now proposed as the Oculina Habitat Area of Particular Concern.

There is no known technique to clean the water column from these oil plumes, and as a consequence the hidden oases of corals in the deep, cold waters of the Gulf of Mexico, the Straits of Florida and the Blake Plateau are in severe danger of being decimated by this oil spill.

The above story is reprinted ( from materials provided by Rosenstiel School of Marine & Atmospheric Science, University of Miami.

Jumping Genes

Schematic drawing of a composite (or complex) transposon. It is composed of two insertion sequence, which codify genes for transposition, flanking structural genes which codify for various proteins or enzymes, i.e. for antibiotic or viral resistance. (Credit: Jacek FH / Courtesy of Wikipedia)

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Jumping Genes Provide Extensive 'Raw Material' for Evolution, Study Finds

Using high-throughput sequencing to map the locations of a common type of jumping gene within a person's entire genome, researchers at the University of Pennsylvania School of Medicine found extensive variation in these locations among the individuals they studied, further underscoring the role of these errant genes in maintaining genetic diversity.

The investigators determined that any two peoples' genomes differ at roughly 285 sites out of the 1139 sites studied. These results were found by scanning the genomes of 25 individuals, 15 of which were unrelated. They report their findings online in Genome Research.

Jumping genes -- also called transposons -- are sequences of DNA that move to different areas of the genome within the same cell.

"The significance of this work is that there is much more diversity in our genome due to insertions by this family of transposons than previously thought," said co-author Haig Kazazian, MD, Seymour Gray Professor of Molecular Medicine, in the Penn Department of Genetics. "This movement of genetic material provides the raw material of genetic evolution, and it doesn't take into account the insertions that we believe occur outside of the sperm and egg cells studied in this project."

Transposons are a source of diversity within a species' gene pool, with implications on many levels. For example, slight changes in genes help organisms adapt and survive in new environments, and populations with genetic diversity are less vulnerable to disease and problems with reproduction.

Insertions into certain spots in the genome can also cause cell function to go awry, so understanding their placement and variation in the human genome is important for a fundamental understanding of disease. Insertions can cause many genetic diseases, such as hemophilia and Duchenne muscular dystrophy, and may play a role in the development of cancer.

Retrotransposons are the major class of jumping genes, with the L1 family the most abundant type of retrotransposon in the human genome. L1s comprise about 17 percent of the human genome and were the subject of the Genome Research paper.

Eventually, continuous jumping by retrotransposons expands the size of the human genome and may cause shuffling of genetic content. For example, when retrotransposons jump, they may take portions of nearby gene sequences with them, inserting these where they land, and thereby allowing for the creation of new genes. Even otherwise unremarkable insertions of L1s may cause significant effects on nearby genes, such as lowering their expression.

Retrotransposons move by having their DNA sequence transcribed or copied to RNA, and then instead of the genetic code being translated directly into a protein sequence, the RNA is copied back to DNA by the retrotransposon's own enzyme called reverse transcriptase. This new DNA is then inserted back into the genome. The process of copying is similar to that of retroviruses, such as HIV, leading scientists to speculate that retroviruses were derived from retrotransposons.

The team also found that on average 1 in 140 individuals have obtained a new L1 insertion from their parents. When all retrotransposon insertions, including L1 and others, are considered about 1 in 40 individuals have received a new insertion from their parents.

The current study counted insertions in the heritable germ cell line, that is in egg and sperm cells. "The real elephant in the room is the question of the incidence of somatic insertions, insertions in cells that aren't eggs or sperm" says Kazazian. "We don't yet know the incidence of those somatic insertions."

Because the insertions detected in this study and others like it are present in some individuals and not others, there is the possibility of association with genetic disease. Future studies in the Kazazian lab funded by an ARRA stimulus grant through the National Institutes of Health will develop techniques to uncover such associations using these retrotransposon insertions as genetic markers.

Adam Ewing, a PhD candidate in the Kazazian lab is the paper's other co-author.

The work was funded by the National Institutes for General Medical Sciences.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Pennsylvania School of Medicine.

Journal Reference:
A. D. Ewing, H. H. Kazazian. High-throughput sequencing reveals extensive variation in human-specific L1 content in individual human genomes. Genome Research, 2010; DOI: 10.1101/gr.106419.110

Unique Eclipsing Binary Star System Discovered

Astrophysicists at UC Santa Barbara are the first scientists to identify two white dwarf stars in an eclipsing binary system, allowing for the first direct radius measurement of a rare white dwarf composed of pure helium. The results will be published in the Astrophysical Journal Letters. These observations are the first to confirm a theory about a certain type of white dwarf star.

The story began with observations by Justin Steinfadt, a UCSB physics graduate student who has been monitoring white dwarf stars as part of his Ph.D. thesis with Lars Bildsten, a professor and permanent member of UCSB's Kavli Institute for Theoretical Physics, and Steve Howell, an astronomer at the National Optical Astronomy Observatory (NOAO) in Tucson, Ariz.

Brief eclipses were discovered during observations of the star NLTT 11748 with the Faulkes Telescope North of the Las Cumbres Observatory Global Telescope (LCOGT), a UCSB-affiliated institution. NLTT 11748 is one of the few very low-mass, helium-core white dwarfs that are under careful study for their brightness variations. Rapid snapshots of the star -- about one exposure every minute -- found a few consecutive images where the star was slightly fainter. Steinfadt quickly realized the importance of this unexpected discovery. "We've been looking at a lot of stars, but I still think we got lucky!" he said.

Avi Shporer, a postdoctoral fellow at UCSB and LCOGT, assisted with the observations and quickly brought his expertise to the new discovery. "We knew something was unusual, especially as we confirmed these dips the next night," Shporer said. The scientists observed three-minute eclipses of the binary stars twice during the 5.6-hour orbit.

The excitement of the discovery and the need to confirm it rapidly led to the use of the 10-meter Keck Telescope, located on Mauna Kea in Hawaii, just five weeks after the first observation. The team also brought in David Kaplan, a Hubble Fellow and KITP postdoctoral fellow. Bildsten and Kaplan arranged for use of the Keck by swapping time they had reserved for another project with Geoff Marcy at UC Berkeley.

During that night, the scientists were able to measure the changing Doppler shift of the star NLTT 11748 as it orbited its faint, but more massive, white dwarf companion. "It was amazing to witness the velocity of this star change in just a few minutes," said Kaplan, who was present at the Keck telescope during the observations.

These observations led to the confirmation of an important theory about white dwarf stars. Stars end their lives in many ways. "The formation of such a binary system containing an extremely low mass helium white dwarf has to be the result of interactions and mass loss between the two original stars," said Howell. White dwarf stars are the very dense remnants of stars like the sun, with dimensions comparable to the earth. A star becomes a white dwarf when it has exhausted its nuclear fuel and all that remains is the dense inner core, typically made of carbon and oxygen.

One of the stars in the newly discovered binary is a relatively rare helium-core white dwarf with a mass only 10 to 20 percent of that of the sun. The existence of these special stars has been known for more than 20 years. Theoretical work predicted that these stars burn hotter and are larger than ordinary white dwarfs. Until now, their size had never been measured. The observations of the star NLTT 11748 by this research group have yielded the first direct radius measurement of an unusual white dwarf that confirms this theory.

The other star in the binary is also a white dwarf, albeit a more ordinary one, composed of mostly carbon and oxygen with about 70 percent of the mass of the sun. This star is more massive and also much smaller than the other white dwarf. The light it gives off is 30 times fainter than that of its partner star in the binary.

Bildsten credits the scientific collaborations at UCSB for the success of this work, noting that the original team was expanded to include KITP, the Physics Department, and LCOGT to quickly respond to the new discovery.

"A particularly intriguing possibility to ponder is what will happen in 6 to 10 billion years," said Bildsten. "This binary is emitting gravitational waves at a rate that will force the two white dwarfs to make contact. What happens then is anybody's guess."

The National Science Foundation, LCOGT, and NASA supported this work.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Santa Barbara.

Journal Reference:
Justin D. R. Steinfadt, David L. Kaplan, Avi Shporer, Lars Bildsten, Steve B. Howell. Discovery of the Eclipsing Detached Double White Dwarf Binary NLTT 11748. The Astrophysical Journal, 2010; 716 (2): L146 DOI: 10.1088/2041-8205/716/2/L146

Copper Nanowires Enable Bendable Displays and Solar Cells

Tiny copper wires can be built in bulk and then "printed" on a surface to conduct current, transparently. (Credit: Benjamin Wiley, Duke Chemistry)

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Copper Nanowires Enable Bendable Displays and Solar Cells; Pin-Like Copper Structures Self-Assemble in Solution

A team of Duke University chemists has perfected a simple way to make tiny copper nanowires in quantity. The cheap conductors are small enough to be transparent, making them ideal for thin-film solar cells, flat-screen TVs and computers, and flexible displays.

"Imagine a foldable iPad," said Benjamin Wiley, an assistant professor of chemistry at Duke. His team reports its findings online in Advanced Materials.

Nanowires made of copper perform better than carbon nanotubes, and are much cheaper than silver nanowires, Wiley said.

The latest flat-panel TVs and computer screens produce images by an array of electronic pixels connected by a transparent conductive layer made from indium tin oxide (ITO). ITO is also used as a transparent electrode in thin-film solar cells.

But ITO has drawbacks: it is brittle, making it unsuitable for flexible screens; its production process is inefficient; and it is expensive and becoming more so because of increasing demand.

"If we are going to have these ubiquitous electronics and solar cells," Wiley said, "we need to use materials that are abundant in the earth's crust and don't take much energy to extract." He points out that there are very few materials that are known to be both transparent and conductive, which is why ITO is still being used despite its drawbacks.

However, Wiley's new work shows that copper, which is a thousand times more abundant than indium, can be used to make a film of nanowires that is both transparent and conductive.

Silver nanowires also perform well as a transparent conductor, and Wiley contributed to a patent on the production of them as a graduate student. But silver, like indium, is rare and expensive. Other researchers have been trying to improve the performance of carbon nanotubes as a transparent conductor, but without much luck.

"The fact that copper nanowires are cheaper and work better makes them a very promising material to solve this problem," Wiley said.

Wiley and his students, PhD candidate Aaron Rathmell and undergraduate Stephen Bergin, grew the copper nanowires in a water-based solution. "By adding different chemicals to the solution, you can control the assembly of atoms into different nanostructures," Wiley said. In this case, when the copper crystallizes, it first forms tiny "seeds," and then a single nanowire sprouts from each seed. It's a mechanism of crystal growth that has never been observed before.

Because the process is water-based, and because copper nanowires are flexible, Wiley thinks the nanowires could be coated from solution in a roll-to-roll process, like newspaper printing, which would be much more efficient than the ITO production process.

Other researchers have produced copper nanowires before, but on a much smaller scale.

Wiley's lab is also the first to demonstrate that copper nanowires perform well as a transparent conductor. He said the process will need to be scaled up for commercial use, and he's got a couple of other problems to solve as well: preventing the nanowires from clumping, which reduces transparency, and preventing the copper from oxidizing, which decreases conductivity. Once the clumping problem has been worked out, Wiley believes the conductivity of the copper nanowires will match that of silver nanowires and ITO.

Wiley, who has applied for a patent for his process, expects to see copper nanowires in commercial use in the not-too-distant future. He notes that there is already investment financing available for the development of transparent conductors based on silver nanowires.

"We think that using a material that is a hundred times cheaper will be even more attractive to venture capitalists, electronic companies and solar companies who all need these transparent electrodes," he said.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Duke University. The original article was written by Mary-Russell Roberson.

Journal Reference:
Aaron R. Rathmell, Stephen M. Bergin, Yi-Lei Hua, Zhi-Yuan Li, Benjamin J. Wiley. The Growth Mechanism of Copper Nanowires and Their Properties in Flexible, Transparent Conducting Films. Advanced Materials, 2010; DOI: 10.1002/adma.201000775

Hubble Catches Stars on the Move

Hubble Catches Stars on the Move: Surprising Signs of Unrest in Massive Star Cluster

With a mass of more than 10 000 suns packed into a volume with a diameter of a mere three light-years, the massive young star cluster in the nebula NGC 3603 is one of the most compact stellar clusters in the Milky Way [1] and an ideal place to test theories for their formation.

A team of astronomers from the Max-Planck Institute for Astronomy in Heidelberg and the University of Cologne led by Wolfgang Brandner (MPIA) wanted to track the movement of the cluster's many stars. Such a study could reveal whether the stars were in the process of drifting apart, or about to settle down.

The cluster, formally known as the NGC 3603 Young Cluster, is about 20 000 light-years from the Sun which makes these measurements extraordinarily difficult. It is necessary to compare images that were made years or even decades apart. The telescope and camera used must give very sharp images and be extremely stable over long periods.

Brandner and his colleagues realised that the Hubble Space Telescope was the best for the job. They found good data in the archives for the NGC 3603 cluster from a July 1997 observing run with the Wide Field Planetary Camera 2 (WFPC2), and then made their own follow-up observations in September 2007, using the same camera and the same set of filters as in the original observations. It then took the team two years of very careful analysis to extract reliable estimates for the motions of stars in the images.

Boyke Rochau (MPIA), the paper's lead author, who performed this analysis as part of his PhD work, explains: "Our measurements have a precision of 27 millionths of an arcsecond per year. This tiny angle corresponds to the apparent thickness of a human hair seen from a distance of 800 km."

In this laborious way, they were able to measure the precise speeds of more than 800 stars. About 50 were identified as foreground stars that are unrelated to the cluster, but more than 700 cluster stars of different masses and surface temperatures remained. The results for the motion of these cluster stars were surprising: this very massive star cluster has not yet settled down. Instead, the stars' velocities were independent of their mass and thus still reflect conditions from the time the cluster was formed, approximately one million years ago.

Stars are born when a gigantic cloud of gas and dust collapses. In cases such as the star forming region NGC 3603, where the cloud is unusually massive and compact, the process is particularly quick and intense. Most of the cloud's matter ends up concentrated inside hot young stars and the cluster keeps much of its initial gravitational attraction [2]. In the long term such massive compact star clusters may lead to the development of the huge balls of stars known as globular clusters, whose tightly packed stars remain held together by gravity for billions of years.

Wolfgang Brandner adds: "This is the first time we have been able to measure precise stellar motions in such a compact young star cluster." Team member Andrea Stolte from the University of Cologne adds: "This is key information for astronomers trying to understand how such clusters are formed, and how they evolve."


Notes


[1] For comparison: in our own immediate stellar neighbourhood, the same volume contains no more than a single star, namely the Sun. The NGC 3603 nebula is located in the central plane of our home galaxy's main disc, in a region called the Carina spiral arm.

[2] More usually the gas cloud is bigger and less massive and only about 10% of this mass ends up inside stars. The remaining gas is then blown away by the fierce ultraviolet light and stellar winds from the hot young stars. Once the interstellar matter is dispersed, the young star cluster has lost nearly 90% of its initial mass and has insufficient gravitational attraction to keep together. The stars in such typical clusters gradually drift apart.

Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by ESA/Hubble Information Centre, via EurekAlert!, a service of AAAS.

Journal Reference:
Boyke Rochau, Wolfgang Brandner, Andrea Stolte, Mario Gennaro, Dimitrios Gouliermis, Nicola Da Rio, Natalia Dzyurkevich, Thomas Henning. Internal dynamics and membership of the NGC 3603 young cluster from microarcsecond astrometry. The Astrophysical Journal, 2010; 716 (1): L90 DOI: 10.1088/2041-8205/716/1/L90

Who Are We Sharing the Planet With?

Who Are We Sharing the Planet With? Millions Less Species Than Previously Thought, New Calculations Suggest

New calculations reveal that the number of species on Earth is likely to be in the order of several million rather than tens of millions. The findings, from a University of Melbourne-led study, are based on a new method of estimating tropical insect species -- the largest and one of the most difficult groups on the planet to study -- having significant implications for conservation efforts.

The study's lead author, Dr Andrew Hamilton from The University of Melbourne's School of Land and Environment, said he was driven to more accurately calculate species numbers because humans were more certain of the number of stars in our galaxy, than fellow species on their own planet.

"Our understanding of species numbers has been clouded by one group of organisms, tropical arthropods, which include insects, spiders, mites and similar organisms. Estimates for this group have ranged from a few million up to 100 million," says Dr Hamilton.

Dr Hamilton and a team of international researchers have applied probability modelling techniques (models often used in financial risk estimates) to data from numerous previous studies. They found that there is a 90% chance that there is somewhere between 2 and 7 million tropical arthropod species, with a best estimate of 3.7 million.

With the addition of approximately 50,000 vertebrates (birds, mammals, amphibians and reptiles), 400,000 plants and possibly 1.3 million other organisms (mostly microorganisms, but excluding the bacteria for which we know very little about), this leaves us with a best estimate of around 5.5 million species with whom we share planet Earth. Furthermore, the study found that there is less than a 0.001% chance that the often-quoted value of at least 30 million total species is true.

"Our study is significant in this the International Year of Biodiversity, giving us a more realistic starting point for estimating extinction rates -- a profound hurdle in conservation biology. Extinction rates are typically estimated through knowing the area of habitat that has been lost, but to know how many species have been lost, we need to know how many were present in the first place. Obviously, if we are starting with less species, we may be worse off than we thought, and also be reducing the complexity of ecosystems even faster," says Dr Hamilton.

"The findings also mean that in spite of 250 years of taxonomic research, around 70% of arthropods await description."

"Many scientists have redone the calculations using different values and arrived at wildly different answers. Our work reran the same calculations, which use various inputs, such as the number of beetle species in the canopy of a typical rainforest tree, but accounted for uncertainty relating to these inputs and, therefore, uncertainty in the final estimation how many species there are."

The study will be published in the current edition of the international journal The American Naturalist.

Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Melbourne.

Journal Reference:
Andrew J. Hamilton, Yves Basset, Kurt K. Benke, Peter S. Grimbacher, Scott E. Miller, Vojtech Novotný, G. Allan Samuelson, Nigel E. Stork, George D. Weiblen, Jian D. L. Yen. Quantifying Uncertainty in Estimation of Tropical Arthropod Species Richness. The American Naturalist, 2010: 100510130432020 DOI: 10.1086/652998