[go: up one dir, main page]

Academia.eduAcademia.edu
SCIENCE NEWS This Week Tsunami Disaster Scientists model the big quake and its consequences The magnitude 9.0 earthquake that struck JI; LI, T. XUE/JOHNS HOPKINS UNIV. the ocean bottom west of Indonesia on the morning of Dec. 26, 2004, triggered several tsunamis that killed an estimated 145,000 coastal residents and tourists, claiming lives on shores even thousands of kilometers away. Researchers are now analyzing the events that led up to the destruction and modeling their possible long-term effects. The largest temblor in 40 years occurred along a subduction zone where the immense fragment of Earth’s crust known as the India plate is forced beneath the Burma plate at an average rate of 6 centimeters per year. Analyses of seismic vibrations produced by the quake place its epicenter just north of the island of Simeulue, which lies about 150 kilometers off the western PUMPED UP The sudden rise of seafloor during the magnitude 9.0 quake of Dec. 26, 2004 (epicenter at star), caused tsunamis that scoured coasts around the Indian Ocean. W W W. S C I E N C E N E W S . O R G coast of Sumatra. From there, at a depth of 18 km, the rupture raced northwest at supersonic speeds for more than 200 seconds, says Chen Ji, a seismologist at the California Institute of Technology in Pasadena. In all, slippage occurred along about 1,200 km of the interface between the tectonic plates—a distance that would span California from north to south with about 100 km to spare. At some spots along the interface, one plate may have slid as much as 20 meters past the other, says Ji. In the most-affected region, a broad expanse of seafloor—and thus the sea above it—was abruptly thrust upward as much as 5 m. The waves spilling away from that sudden bump raced across the Indian Ocean at jetliner speeds, says Ji. The first tsunami may have been 15 m high when it slammed into Sumatran shores about 15 minutes after the quake. Satellite photos taken after the disaster indicate that the tsunamis deposited beach sand and soil or stripped away vegetation as much as 3 km inland along much of Sumatra’s western coast. As of press time, the death toll in Sumatra was estimated to be in excess of 94,000. Sites farther from the quake zone experienced smaller but nevertheless deadly waves. Particularly affected were Thailand, which was struck by tsunamis about 75 minutes after the quake occurred, and Sri Lanka and India, which were pounded by devastating waves about 4 hours after the temblor. Death reached more than 5,000 km to African shores, claiming beachgoers and fishermen from Somalia to Kenya. Notably, the Indian Ocean lacks a tsunami-warning system like the network of buoys and deep-sea instruments that monitors earthquake and wave activity in the Pacific Ocean (SN: 3/6/04, p. 152). Although portions of the ocean floor rose in many places as a result of the Dec. 26 quake, Ji’s geophysical models suggest that the seafloor sank as much as 2 m in other locales. Even some land was affected. Parts of western Sumatra may have permanently lost as much as 1 m in elevation. Other effects of the temblor are subtle. The sudden surge of the India plate downward, toward the planet’s center, slightly altered the planet’s distribution of mass, says Richard S. Gross of NASA’s Jet Propulsion Laboratory in Pasadena. Just as spinning skaters rotate more quickly when they draw their arms inward toward their bodies, the Earth now completes its daily rotation in about 2.67 microseconds less time than it did before the quake, according to his calculations. The region struck by the massive quake had previously been identified as one of about 80 areas likely to be stricken by a temblor of magnitude 7.0 or greater in the years between 2000 and 2010. Between 1990 and 2000, the region near the Dec. 26 temblor’s epicenter had experienced an above-average rate of earthquakes with magnitude 5.0 and above, says Donald L. Turcotte of the University of California, Davis. —S. PERKINS Beat Generation Genetically modified stem cells repair heart In experiments on guinea pigs, scientists have used genetically modified human embryonic stem cells to make a biological pacemaker. The implanted tissue has kept the guinea pig hearts beating after their natural pacemaker cells were destroyed. The researchers, led by Ronald A. Li of Johns Hopkins University in Baltimore, began with unspecialized embryonic stem cells. The scientists genetically modified them to produce green fluorescent protein. When they separated the cells into small clusters, the cells began to differSTEM CELL POWER entiate. Some A cluster of genetically clusters started modified human to beat, indicatpacemaker cells, about ing the presence 200 micrometers across, of heart-muscle glows green atop an cells and pacearray of tiny electrodes maker cells. The that detects its beats. researchers then extracted cells from the beating clusters. After transferring these cells into the animals, the scientists used a freezing probe to kill the animals’ own pacemaker tissue. Despite the loss of their natural pacemakers, the guinea pigs’ hearts continued to beat. Close examination showed that the rhythm was originating from the areas where the human cells had been implanted. Unlike battery-powered pacemakers, says Li, stem cell–based pacemakers speed up or slow down in response to drugs that alter normal heart rate. The researchers aren’t sure why the guinea pigs’ immune systems didn’t destroy the intruding human cells. According to Li, the guinea pigs’ circulatory systems may not have thoroughly branched into the human cells and so the animals’ immune systems may not have detected them. Li’s study, to appear in an upcoming JANUARY 8, 2005 VOL. 167 19 SCIENCE NEWS This Week Temples of Boom Ancient Hawaiians took fast road to statehood Around 400 years ago, the residents of two Hawaiian islands built stone temples at a dizzying pace over the course of a generation or two, a new study finds. A construction boom of that kind and magnitude reflected the surprisingly rapid formation of a fledgling political state out of formerly independent populations, investigators say. Until now, many researchers assumed that chiefs of various communities on the islands of Maui and Molokai had directed construction of temples over a span of approximately 250 years. New age estimates of the temples indicate that they were built within a much narrower window of time, say Patrick V. Kirch of the University of California, Berkeley and 20 JANUARY 8, 2005 VOL. 167 STATE BUILDERS Dating of coral found in the remains of prehistoric Hawaiian temples such as this one, shown from above, unveils a period of rapid state formation. Warren D. Sharp of the Berkeley Geochronology Center. The revised dates come from pieces of sea coral that were placed in special wall compartments during dedications of new temples. Southeastern Maui contains the remnants of 30 temples that were constructed within a 60-year span, between A.D. 1580 and A.D. 1640, Kirch and Sharp report in the Jan. 7 Science. The results coincide with the accounts of native Hawaiians, recorded by 19th-century Spanish missionaries, that a single leader assumed control of at least two formerly independent communities on Maui around A.D. 1600. Anthropologists typically treat such accounts as myths, Kirch says. “I was surprised by the new dates for these temples,” he remarks. “This is tangible evidence for the speed with which an archaic state formed in Hawaii.” An archaic state is a political system with several social classes, as well as rulers who claim power on the basis of their special relationships to gods. Bureaucracies, armies, and an early form of taxation first emerged in archaic states. Kirch and Sharp analyzed seven coral offerings from what they regard as a representative sample of temples on Maui, as well as one piece of coral from a large temple on Molokai. The preservation of delicate branches and surface structures on the specimens show that local people collected live coral from shallow waters and deposited it in a temple the same day, the scientists say. The researchers measured ratios of specific forms of uranium and thorium in the coral specimens to calculate their ages. This technique is more precise than previous radiocarbon measurements of the ages of wood and charcoal unearthed in the temples, Kirch and Sharp say. State formation capped a period of population growth and expansion of agriculture on the island, Kirch theorizes. Pre- historic settlers probably first reached Maui around A.D. 1400. A relatively speedy transition from villagebased life to stratified societies also occurred in ancient Mexico, say Joyce Marcus and Kent V. Flannery, both of the University of Michigan in Ann Arbor. New radiocarbon dates for sites in the Valley of Oaxaca indicate that only about 1,300 years elapsed between construction of the oldest-known ritual building, where village men gathered for ceremonies, and the first state temple. Marcus and Flannery’s results will appear in the Proceedings of the National Academy of Sciences. —B. BOWER Reflections on Insecticides Mirror forms of agrochemicals set risk Mirror, mirror, on the wall, what’s the most hazardous pesticide form of all? Such is the question that scientists and regulators should be asking as they evaluate the environmental effects of pesticides, new research suggests. Many molecules, like gloves of a pair, exist in mirror-image forms. A team of environmental researchers has found that for some insecticides, one mirror-image variant, or enantiomer, is more toxic or degrades more slowly in the environment than its counterpart does. Since pesticides typically are mixtures of both enantiomers of a pair, understanding the differences between the two could lead to more-effective and less environmentally hazardous agrochemicals. Although different enantiomers of the same molecule are identical chemically and physically, they can have dramatically different biological activities. “As a result, they interact differently with microbes in SCIENCE NEWS KIRCH Circulation, isn’t the first to use stem cells to repair broken hearts, but it’s the first to do it with genetically modified cells. The resulting green glow made the human cells easy to spot in the guinea pigs, but more important, says Li, it’s proof that genetic modification didn’t disrupt the cells’ development. “Now, we can move on to something more ambitious,” he says. His group has already learned how to genetically alter human pacemaker cells to fine-tune their firing rates, though the scientists have yet to test these modified cells in animals. Adjusting the firing rate could be important because ordinary pacemaker cells beat slowly when implanted. The heart’s natural pacemaker is a complex mixture of several cell types, Li says, so it’s difficult to mimic its function with any single, unmodified cell type. Gordana Vunjak-Novakovic of the Massachusetts Institute of Technology, who investigates techniques for growing replacement heart tissue, says that although many groups are working to engineer heart tissue, Li’s study stands out because it investigates what happens after the engineered tissue is implanted. Still, she cautions that much work remains before heart-repair treatments can be developed for people. “We cannot even complete a list of hurdles at this time or predict how long it will take to resolve some of the problems we are working on,” she says. —D. SHIGA