This month in Science Roundup:
Distributed Computing
A Solid Lighting Future
Direct Oil Dating
The Great Sumatra-Andaman Earthquake
Earth's Changing Reflectivity
Cassini Reveals Titan
Rebuilding a Mammoth Ecosystem
Patient-Specific Stem Cells
Tracing Human Migrations
Leprosy's Travels
Gun Violence Begets Violence
A New Kind of Monkey
Powered Plants
Powerful scientific instruments from genome-sequencing machines to orbiting telescopes are generating massive amounts of information faster than our available computing power can possibly keep up with. To accommodate this data deluge, researchers are finding ways to parcel big computing jobs into smaller packages and distribute them to underused computers on the Internet. A special section of the 6 May 2005 Science explored the new frontiers of scientific analysis being opened up by the growing fields of distributed and grid computing. Two News features described how millions of computers across the globe are making use of idle screen-saver time to crunch data for projects as diverse as searching for extraterrestrial intelligence, climate-change prediction, and mapping the Internet. Viewpoint articles focused on the scientific promise of efforts such as the Semantic Web and other projects to tie the world's scientific cyberinfrastructure together through a set of standardized interfaces and protocols. Meanwhile, Science's online companion STKE ( http://stke.sciencemag.org/ ) looked at the still-tricky business of extracting meaning automatically from vast sets of metabolic, signaling, and protein data. And a related Editorial by E. D. Lazowska and D. A. Patterson considered how recent changes in U.S. funding policies threaten to derail further innovation in information technology.
Conventional incandescent and fluorescent light sources illuminate much of the world, but their efficiency is limited by fundamental factors like filament temperature that cannot be overcome. In a Review in the 27 May 2005 Science, E. F. Schubert and J. K. Kim ( http://www.sciencemag.org/cgi/content/short/308/5726/1274 ) discussed the principles and applications of solid-state lighting, the efficiency of which is "limited only by human creativity and imagination." In addition to providing energy savings and environmental benefits, solid-state light sources like light-emitting diodes (LEDs) offer controllability of properties such as spectral power distribution, color temperature, and polarization. Such "smart" light sources can adjust to specific environments and requirements -- a desirable property for applications in transportation, agriculture, and even medicine. As noted in a related Policy Forum by E. Mills ( http://www.sciencemag.org/cgi/content/short/308/5726/1263 ), solid-state lighting would not only reduce global lighting costs and greenhouse gas emissions, but provide tremendous opportunity for those without access to electricity in the developing world.
Petroleum deposits typically form when oil generated from source rocks collects beneath relatively impermeable rocks, or some other geologic trap. Migration of this oil usually occurs long after the source rocks are deposited, making it difficult to determine where exactly the hydrocarbons came from and when they formed -- information that would be helpful to future petroleum exploration efforts. In a Report in the 27 May 2005 Science, D. Selby and R. A. Creaser ( http://www.sciencemag.org/cgi/content/short/308/5726/1293 ) showed that oil contains enough rhenium and osmium, inherited from organic-rich source rocks, to provide direct dates for when the hydrocarbons migrated and accumulated (data that has previously only been inferred from the ages of surrounding rock). By measuring the decay of rhenium to osmium, the team determined that oil from the great oil sand deposits of Alberta, Canada, accumulated about 112 million years ago. Moreover, rhenium-osmium profiles from a variety of deposits within this giant deposit show similar characteristics, supporting the notion of a single source for these hydrocarbons. As noted in an accompanying Perspective by B. F. Schaefer ( http://www.sciencemag.org/cgi/content/short/308/5726/1267 ), broader application of the technique may provide insight into where and when oil is likely to accumulate.
The Great Sumatra-Andaman Earthquake
http://www.sciencemag.org/cgi/content/summary/308/5725/1125The 26 December 2004 Sumatra-Andaman earthquake was the largest seismic event on Earth in more than 40 years. It released an amount of energy equivalent to a 100-gigaton bomb and generated a tsunami that caused more that 283,000 deaths. A special section of the 20 May 2005 Science described the physical details of this great quake and some of its effects. As noted in a Viewpoint article by R. Bilham, the Sumatra-Andaman earthquake was a surprisingly complex event that began gradually, exploded to life and then tapered off slowly. Four research papers reported seismic, satellite, and Global Positioning System (GPS) observations that offer insight into what happened and how. Reconstructions of the 1300-meter rupture -- which occurred at the Indo-Australian plate boundary -- show that after the initial rapid rupture, subsequent slip of the plate interface occurred with decreasing speed toward the north producing low-period seismic waves that were detectable for weeks. Effects of the earthquake were felt halfway around the world in Alaska, where surface waves triggered a swarm of 14 local earthquakes near Mount Wrangell. And a related Report by Banerjee et al. ( http://www.sciencemag.org/cgi/content/abstract/1113746v3 ) published Science Express on 19 May indicates that considerable energy was released more than one hour after the earthquake started and after the full fault had erupted. These and other data provide a new basis for understanding the largest, rarest, and most destructive seismic events.
Earth's climate is governed by the balance between the amount of solar radiation reaching Earth's surface (insolation) the amount of outgoing long-wave radiation. Many studies have reported evidence of a significant decrease in insolation during the past 40 years, but how much it has varied and why is poorly understood. Now, two Reports in the 6 May 2005 Science have presented independent observations that show that the amount of sunlight reaching Earth's surface has increased since about 1990. Pinker et al. ( http://www.sciencemag.org/cgi/content/short/308/5723/850 ) analyzed satellite records from 1983 to 2001 and concluded that while insolation decreased in the earlier part of the record (a phenomenon known as global dimming), the negative trend reversed around 1990 and was followed by an even larger increase. The recent brightening trend was corroborated by Wild et al. ( http://www.sciencemag.org/cgi/content/short/308/5723/847 ), who examined a large set of surface-based measurements starting in 1990, and found that the amount of sunlight at Earth's surface has increased since the late 1980s. In a related Brevium, Wielicki et al. ( http://www.sciencemag.org/cgi/content/short/308/5723/825 ) reported an estimate of Earth's albedo -- the fraction of incident solar radiation that is reflected back to space. Their global satellite data fail to confirm the recent suggestion that, since 2001, Earth has reflected more incident sunlight. As noted in an accompanying Perspective by Charlson et al. ( http://www.sciencemag.org/cgi/content/short/308/5723/806 ) discrepancies in these observations are still large, and the effects of cloud coverage and the abundance of atmospheric aerosols are unclear. Sustained, direct, and simultaneous observations of albedo with all available methods are needed to provide a more precise picture of Earth's reflectivity.
http://www.sciencemag.org/cgi/content/summary/308/5724/968On 1 July 2004, the Cassini Orbiter spacecraft dropped into orbit around Saturn, capturing unprecedented details of the planet's signature icy rings along the way. Now, a special section of the 13 May 2005 Science highlights results from Cassini's first two passes by Titan, Saturn's largest moon, including a trip through its uppermost atmosphere. Radar images reveal a relatively young, flat Titan surface with few impact craters, but with evidence of surface flows and ice volcanism. Data from a variety of Cassini's spectrometers provided new information about Titan's primitive nitrogen and methane-rich atmosphere, which may resemble that hypothesized for early Earth -- before microbial activity and other life transformed it into a more oxidized state. Cassini also captured temperature and wind profiles and measured the effects of Titan's passage through Saturn's magnetic field. The spacecraft is planning to revisit Titan more than 40 times during its mission, repeating many of these analyses and mapping different parts of the moon's surface. Together with insights from the Huygens probe, which landed on Titan's surface in January 2005, these data should help us understand the origin and evolution of Saturn's largest moon and, by analogy, Earth's early history.
Rebuilding a Mammoth Ecosystem
The mammoth steppe, a vibrant ecosystem of grasslands and vast populations of large grazing animals including mammoths, wooly rhinos, horses, and bison, extended from Western Europe through Siberia during the last ice age. About 10,000 years ago, when the Pleistocene epoch gave way to the warmer Holocene, the steppe completely disappeared. Many scientists believe that it was the sudden and severe shift to a warmer and moister climate that proved catastrophic to the steppe vegetation and the animals that thrived on them. But Sergey Zimov, director of the Northeast Science Station in Cherskii, and author of this month's "Global Voices of Science" essay ( 6 May 2005 ; http://www.sciencemag.org/cgi/content/short/308/5723/796 ), thinks otherwise. He argues that changing hunting practices wiped out the great herds of animals whose absence led to the ecosystem shifts. To test that hypothesis, Zimov and his colleagues have spent the past decade trying to restore the mammoth steppe in one modest parcel of the northern Siberian region of Yakutia that they call Pleistocene Park. By reintroducing animals such as Yakutian horses and bison, they hope to determine the role that Pleistocene animals played in maintaining their own habitat and better understand the forces that ultimately vanquished the long-gone ecosystem. An online slideshow ( http://www.sciencemag.org/sciext/globalvoices/ ) highlighted their efforts.
Last year, South Korean team Hwang et al. reported the first derivation of human embryonic stem (ES) cells by a process called somatic cell nuclear transfer, or SCNT ( 12 March 2004; http://www.sciencemag.org/cgi/content/short/303/5664/1669 ), which involves replacing the nucleus of a human oocyte with one from a different cell, and then stimulating development of the egg. In a Report published online Science Express on 19 May 2005 ( http://www.sciencemag.org/cgi/content/abstract/1112286 ), the same team described the creation of eleven new human ES cell lines that for the first time carry the genetic signature of diseased or injured patients. Moreover, the breakthrough represents a 10-fold increase in the efficiency of creating such lines (from 1 in 200+ to more than 1 in 20), and may eventually pave the way for development of stem cells that could be used in treating conditions such as spinal cord injury or Parkinson's disease. The researchers say that one important factor to their success was the use of freshly harvested oocytes from fertile women instead of ones left over from fertility treatments. As noted in a related Policy Forum by D. Magnus and M. K. Cho also published Science Express ( http://www.sciencemag.org/cgi/content/abstract/1114454 ), the achievement raises ethical and policy questions about oocyte donation -- a generally safe procedure, but one that is not immune to serious complications. A News story by G. Vogel in the 20 May issue ( ) put the breakthrough in the context of the ongoing debate over stem cell research.
Much of what we know about early human migration comes from studies of maternally inherited mitochondrial DNA (mtDNA) from existing populations. Because the amount of sequence variation among different groups generally reflects the amount of time since the groups diverged from each other, scientists have been able to piece together a map of human colonization. The proposal that early humans migrated out of Africa to Eurasia between 55,000 and 85,000 years ago is widely accepted, but the route they took is still disputed. Two studies of southeast Asian populations reported in the 13 May 2005 Science now suggest that the earliest humans traveled along the Indian Ocean coastline, rather than through the Middle East, as the traditional model suggests. Thangaraj et al. ( http://www.sciencemag.org/cgi/content/short/308/5724/996 ) studied indigenous tribal populations on the Andaman Islands between India and Myanmar and identified two mtDNA types, which suggest that these populations became genetically isolated from other southeast Asian populations about 50,000 and 70,000 years ago, apparently after their initial migration from Africa. This timing is supported by results from Macaulay et al. ( http://www.sciencemag.org/cgi/content/short/308/5724/1034 ), who sampled aboriginal inhabitants of Malaysia called the Orang Asli. mtDNA genome analysis indicates that this population likely branched off from other Asian lineages around 60,000 years ago, soon after their ancestors left Africa. Moreover, the researchers argue that the phylogenetic patterns they observe support only one model -- that of a single dispersal event about 65,000 years ago along the coast from East Africa through India and onward into Southeast Asia and Australasia. They further propose that an early offshoot led to the settlement of the Near East and Europe, but that the main dispersal from India to Australia was rapid, taking only a few thousand years. A Perspective by P. Forster and S. Matsumura ( http://www.sciencemag.org/cgi/content/short/308/5724/965 ) discussed the new findings.
Leprosy is a chronic and puzzling disease characterized by deforming lesions and nerve damage. Caused by a slowly developing infection with the bacterium Mycobacterium leprae, it has plagued human populations for thousands of years. Popular theory about how leprosy spread worldwide holds that it originated in India and was brought to Europe by Alexander the Great's soldiers returning from conquest. Now, a study of several M. leprae strains collected from around the globe challenges that theory. In a Report in the 13 May 2005 Science, Monot et al. ( http://www.sciencemag.org/cgi/content/short/308/5724/1040 ) used comparative genomics to show that all extant cases of leprosy are attributable to a single clone of the bacterium, which seems to have broken into just four types. The team's analysis of single-nucleotide DNA differences among various strains suggests that the disease originated in East Africa or Central Asia and spread eastward and westward with successive human migrations. The data also indicate that Europeans or North Africans introduced leprosy into West Africa and that colonialism and the slave trade brought the disease to the Caribbean and the Americas within the past 500 years. An accompanying News story by D. Grimm ( http://www.sciencemag.org/cgi/content/short/308/5724/936a ) highlighted the report.
Although researchers have found a connection between exposure to violence and violent behavior, they have had difficulty proving that the first causes the second. In a Report in the 27 May 2005 Science, Bingenheimer et al. ( http://www.sciencemag.org/cgi/content/short/308/5726/1323 ) discuss results from a longitudinal study of more than 1000 Chicago adolescents, which suggest that exposure to gun violence more than doubles the likelihood that an adolescent will perpetrate a violent or aggressive act within the following 2 years. The team used a relatively new, and controversial technique called "propensity score stratification" to create, through statistical means, a randomized experiment on propensity toward violence from observational data. Subjects were first ranked according to "propensity" scores: a cumulative tally of 153 risk factors that estimated the probability of exposure to gun violence. The researchers then compared adolescents who were equally likely to be exposed but whose actual exposure status differed. Although there is not possible to remove all potential confounding factors, the team argues that this method allowed them to control for a host of individual, family, peer, and neighborhood variables. As noted in an accompanying News story by C. Holden ( http://www.sciencemag.org/cgi/content/short/308/5726/1239a ) the new study "may once again stoke up the debate over juvenile violence."
In the wooded highlands of Tanzania lives a long-tailed, black-faced monkey that until now has eluded our catalogues of biodiversity. In a Report in the 20 May 2005 Science Jones et al. ( http://www.sciencemag.org/cgi/content/short/308/5725/1161 ) reported on the independent, but nearly simultaneous discovery of two populations of a new species of African monkey named the highland mangabey or Lophocebus kipunji. Although researchers need to sample the monkey's DNA to determine how closely related it is to other mangabeys, the new species -- which sports an upright crest on its forehead and emits a distinctive "honk-bark" call -- looks and sounds quite different from its relatives. Less than 1,000 individuals are believed to exist, and the researchers expect the highland mangabey to be classified as a critically endangered species. An accompanying News story by M. Beckman ( http://www.sciencemag.org/cgi/content/short/308/5725/1103a ) highlighted the discovery.
Most plants and fungi move too slowly to even notice, but a few species use lighting reflexes to trap food or spew their seeds. According to a Report by J. M. Skotheim and L. Mahadevan ( http://www.sciencemag.org/cgi/content/short/308/5726/1308 ) in the 27 May 2005 Science, species capable of these rapid movements can be can be divided into two groups: those that swell and shrink their cells to generate relatively small, slow movement and those that use swelling and shrinking to trigger the release of built-up energy through the tearing, snapping or buckling of tissue. Species that fall into the latter group include the Venus flytrap, which uses energy stored in the leaves' elastic tissue, causing them to buckle and snap shut, and the desert petunia, which relies on pressure built up in its tissue for an explosive fracture to disperse seeds. The researchers found that how plants and fungi move, and at what speeds, is ultimately determined by the physics of water flow through their tissues and the rate of fluid transport. The new study may offer insights into how to design mechanical systems that are driven by hydraulic forces. A related ScienceNOW story by N. Inman ( http://sciencenow.sciencemag.org/cgi/content/full/2005/527/2 ) highlighted the report.