Evolutionary Accident Probably Caused The Worst Snowball Earth Episode, Study Shows

PASADENA--For several years geologists have been gathering evidence indicating that Earth has gone into a deep freeze on several occasions, with ice covering even the equator and with potentially devastating consequences for life. The theory, known as "Snowball Earth," has been lacking a good explanation for what triggered the global glaciations.

Now, the California Institute of Technology research group that originated the Snowball Earth theory has proposed that the culprit for the earliest and most severe episode may have been lowly bacteria that, by releasing oxygen, destroyed a key gas keeping the planet warm.

In the current issue of the Proceedings of the National Academy of Sciences (PNAS), Caltech graduate student Robert Kopp and his supervising professor, Joe Kirschvink, along with alumnus Isaac Hilburn (now a graduate student at the Massachusetts Institute of Technology) and graduate student Cody Nash, argue that cyanobacteria (or blue-green algae) suddenly evolved the ability to break water and release oxygen about 2.3 billion years ago. Oxygen destroyed the greenhouse gas methane that was then abundant in the atmosphere, throwing the global climate completely out of kilter.

Though the younger sun was only about 85 percent as bright as it is now, average temperatures were comparable to those of today. This state of affairs, many researchers believe, was due to the abundance of methane, known commercially as natural gas. Just as they do in kitchen ranges, methane and oxygen in the atmosphere make an unstable combination; in nature they react in a matter of years to produce carbon dioxide and water. Though carbon dioxide is also a greenhouse gas, methane is dozens of times more so.

The problem began when cyanobacteria evolved into the first organisms able to use water in photosynthesis, releasing oxygen into the environment as a waste product. More primitive bacteria depend upon soluble iron or sulfides for use in photosynthesis; the switch to water allowed them to grow almost everywhere that had light and nutrients. Many experts think this happened early in Earth history, between 3.8 and 2.7 billion years ago, in which case some process must have kept the cyanobacteria from destroying the methane greenhouse for hundreds of millions of years. The Caltech researchers, however, find no hard evidence in the rocks to show that the switch to water for photosynthesis occurred prior to 2.3 billion years ago, which is about when the Paleoproterozoic Snowball Earth was triggered.

For cyanobacteria to trigger the rapid onset of a Snowball Earth, they must have had an ample supply of key nutrients like phosphorous and iron. Nutrient availability is why cyanobacterial blooms occur today in regions with heavy agricultural runoff.

Fortunately for the bacteria, Earth 2.3 billion years ago had already entered a moderately cold period, reflected in glacially formed rocks in Canada. Measurements of the magnetization of these Canadian rocks, which the Caltech group published earlier this year, indicate that the glaciers that formed them may have been at middle latitudes, just like the glaciers of the last ice age.

The action of the glaciers, grinding continental material into powder and carrying it into the oceans, would have made the oceans rich in nutrients. Once cyanobacteria evolved this new oxygen-releasing ability, they could feast on this cornucopia, turning an ordinary glaciation into a global one.

"Their greater range should have allowed the cyanobacteria to come to dominate life on Earth quickly and start releasing large amounts of oxygen," Kopp says.

This was bad for the climate because the oxygen destabilized the methane greenhouse. Kopp and Kirschvink's model shows that the greenhouse may have been destroyed in as little as 100,000 years, but almost certainly was eliminated within several million years of the cyanobacteria's evolution into an oxygen-generating organism. Without the methane greenhouse, global temperatures plummeted to -50 degrees Celsius.

The planet went into a glacial period so cold that even equatorial oceans were covered with a mile-thick layer of ice. The vast majority of living organisms died, and those that survived, either underground or at hydrothermal vents and springs, were probably forced into bare subsistence. If correct, the authors note, then an evolutionary accident triggered the world's worst climate disaster.

However, in evolving to cope with the new influx of oxygen, many survivors gained the ability to breathe it. This metabolic process was capable of releasing much energy and eventually allowing the evolution of all higher forms of life.

Kirschvink and his lab have earlier shown a mechanism by which Earth could have gotten out of Snowball Earth. After some tens of millions of years, carbon dioxide would build up to the point that another greenhouse took place. In fact, the global temperature probably bounced back to +50 degrees Celsius, and the deep-sea vents that provided a refuge for living organisms also had steadily released various trace metals and nutrients. So not only did life return after the ice layers melted, but it did so with a magnificent bloom.

"It was a close call to a planetary destruction," says Kirschvink. "If Earth had been a bit further from the sun, the temperature at the poles could have dropped enough to freeze the carbon dioxide into dry ice, robbing us of this greenhouse escape from Snowball Earth."

Of course, 2.3 billion years is a very long time ago. But the episode points to a grim reality for the human race if conditions ever resulted in another Snowball Earth. We who are living today will never see it, but Kirschvink says that an even worse Snowball Earth could occur if the conditions were again right.

"We could still go into Snowball if we goof up the environment badly enough," he says. "We haven't had a Snowball in the past 630 million years, and because the sun is warmer now it may be harder to get into the right condition. But if it ever happens, all life on Earth would likely be destroyed. We could probably get out only by becoming a runaway greenhouse planet like Venus."

Kirschvink is Caltech's Van Wingen Professor of Geobiology.

The PNAS paper is titled "The Paleoproterozoic Snowball Earth: A Climate Disaster Triggered by the Evolution of Oxygenic Photosynthesis."

 

 

 

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Robert Tindol
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Planetary Scientists Discover Tenth Planet

PASADENA, Calif.--A planet larger than Pluto has been discovered in the outlying regions of the solar system with the Samuel Oschin Telescope at Palomar Observatory, California Institute of Technology planetary scientist Mike Brown announced today.

The planet is a typical member of the Kuiper belt, but its sheer size in relation to the nine planets already known means that it can only be classified as a planet, Brown says. Currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), the planet becomes the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects.

"It will be visible over the next six months and is currently almost directly overhead in the early-morning eastern sky, in the constellation Cetus," says Brown, who made the discovery with colleagues Chad Trujillo, of the Gemini Observatory, and David Rabinowitz, of Yale University, on January 8.

Brown and Trujillo first photographed the new planet with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of this year. In the last seven months, the scientists have been studying the planet to better estimate its size and its motions.

"It's definitely bigger than Pluto," says Brown, who is professor of planetary astronomy. Scientists can infer the size of a solar-system object by its brightness, just as one can infer the size of a faraway light bulb if one knows its wattage. The reflectance of the planet is not yet known--in other words, it's not yet possible to tell how much light from the sun is reflected away--but the amount of light the planet reflects puts a lower limit on its size.

"Even if it reflected 100 percent of the light reaching it, it would still be as big as Pluto," says Brown. "I'd say it's probably one and a half times the size of Pluto, but we're not sure yet of the final size.

"But we are 100 percent confident that this is the first object bigger than Pluto ever found in the outer solar system."

Determination of the upper limit of the size of the planet is constrained by results from the Spitzer Space Telescope, which has already proved its mettle in studying the heat of dim, faint, faraway objects such as the Kuiper-belt bodies. Because the Spitzer is unable to detect the new planet, the overall diameter must be less than 3,000 kilometers, Brown says. A name for the new planet has been proposed by the discoverers to the International Astronomical Union, and they are awaiting the decision of this body before announcing the name.

The research is funded by NASA. For more information see http://www.gps.caltech.edu/~mbrown

Samuel Oschin Telescope: http://www.astro.caltech.edu/palomarnew/sot.html

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RT

KamLAND Detector Provides New Way to Study Heat from Radioactive Materials Within Earth

PASADENA, Calif.--Much of the heat within our planet is caused by the radioactive decay of the elements uranium and thorium. Now, an international team of particle physicists using a special detector in Japan has demonstrated a novel method of measuring that radioactive heat.

In the July 28 issue of the journal Nature, the physicists report on measurements of electron antineutrinos they have detected from within Earth by using KamLAND, the Kamioka Liquid Scintillator Anti-Neutrino Detector. These data indicate that Earth itself generates about 20 billion kilowatts (or terawatts) of power from underground radioactive decays.

According to Robert McKeown, a physicist at the California Institute of Technology and one of the authors of the paper, the results show that this novel approach to geophysical research is feasible. "Neutrinos and their corresponding antiparticles, antineutrinos, are remarkable for their ability to pass unhindered through large bodies of matter like the entire Earth, and so can give geophysicists a powerful method to access the composition of the planet's interior."

McKeown credits the discovery with the unique KamLAND experimental apparatus. The antineutrino detector was primarily built to study antineutrinos emitted by Japanese nuclear power plants. The KamLAND experiment has already resulted in several breakthroughs in experimental particle physics, including the 2002 discovery that antineutrinos emitted by the power plants do indeed change flavor as they travel through space. This result helped solve a longstanding mystery related to the fact that the number of neutrinos from the sun was apparently too small to be reconciled with our current understanding of nuclear fusion. The new results turn from nuclear reactors and the sun to the Earth below. To detect geoneutrinos (or antineutrinos arising from radioactive decays within the planet), the researchers carefully shielded the detector from background radiation and cosmic sources, and also compensated for the antineutrinos that have come from Japan's 53 nuclear power reactors.

The decays of both uranium and thorium have been well understood for decades, with both decays eventually resulting in stable isotopes of lead. KamLAND is the first detector built with the capability to detect the antineutrinos from these radioactive decays.

The researchers plan to continue running the KamLAND experiments for several years. By reducing the trace residual radioactivity in the detector, they hope to increase the sensitivity of the experiment to geoneutrinos and neutrinos from the sun. The additional data will also allow them to better constrain the oscillation of neutrinos as they change their flavors, and perhaps to catch neutrinos from interstellar space if any supernovae occur in our galaxy.

Other members of McKeown's team at Caltech's Kellogg Radiation Lab are Christopher Mauger, a postdoctoral scholar in physics, and Petr Vogel, a senior research associate emeritus in physics. Other partners in the study include the Research Center for Neutrino Science at Tohuku University in Japan, the University of Alabama, the University of California at Berkeley and the Lawrence Berkeley National Laboratory, Drexel University, the University of Hawaii, the University of New Mexico, the University of North Carolina, Kansas State University, Louisiana State University, Stanford University, Duke University, North Carolina State University, the University of Tennessee, the Institute of High Energy Physics in Beijing, and the University of Bordeaux in France.

The project is supported in part by the U.S. Department of Energy.

 

 

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Robert Tindol
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Mars Has Been in the Deep Freeze for the Past Four Billion Years, Study Shows

PASADENA, Calif.--The current mean temperature on the equator of Mars is a blustery 69 degrees below zero Fahrenheit. Scientists have long thought that the Red Planet was once temperate enough for water to have existed on the surface, and for life to possibly have evolved. But a new study by Caltech and MIT scientists gives this idea the cold shoulder.

In the July 22 issue of the journal Science, Caltech graduate student David Shuster and MIT assistant professor Benjamin Weiss (formerly a Caltech student) report that their studies of Martian meteorites demonstrate that at least several rocks originally located near the surface of Mars have been freezing cold for four billion years. Their work is a novel approach to extracting information on the past climate of Mars through the study of Martian meteorites.

In fact, the evidence shows that during the last four billion years, Mars has likely never been sufficiently warm for liquid water to have flowed on the surface for extended periods of time. This implies that Mars has probably never had a hospitable environment for life to have evolved, unless life could have gotten started during the first half-billion years of its existence, when the planet was probably warmer.

The work involves two of the seven known "nakhlite" meteorites (named after El Nakhla, Egypt, where the first such meteorite was discovered), and the celebrated ALH84001 meteorite that some scientists believe shows evidence of microbial activity on Mars. Using geochemical techniques, Shuster and Weiss reconstructed a "thermal history" for each of the meteorites to estimate the maximum long-term average temperatures to which they were subjected.

"We looked at meteorites in two ways," says Weiss. "First, we evaluated what the meteorites could have experienced during ejection from Mars, 11 to 15 million years ago, in order to set an upper limit on the temperatures in a worst-case scenario for shock-heating."

Their conclusions were that ALH84001 could never have been heated to a temperature higher than 650 degrees Fahrenheit for even a brief period of time during the last 15 million years. The nakhlites, which show very little evidence of shock-damage, were unlikely to have been above the boiling point of water during ejection 11 million years ago.

Although these are still rather high temperatures, the other part of the research addressed the long-term thermal history of the rocks while they resided on Mars. They did this by estimating the total amount of argon still remaining in the samples, using data previously published by two teams at the University of Arizona and the NASA Johnson Space Center.

The gas argon is present in the meteorites as well as in many rocks on Earth as a natural consequence of the radioactive decay of potassium. As a noble gas, argon is not very chemically reactive, and because the decay rate is precisely known, geologists for years have measured argon as a means of dating rocks.

However, argon is also known to "leak" out of rocks at a temperature-dependent rate. This means that if the argon remaining in the rocks is measured, an inference can be made about the maximum heat to which the rock has been subjected since the argon was first made. The cooler the rock has been, the more argon will have been retained. Shuster and Weiss's analysis found that only a tiny fraction of the argon that was originally produced in the meteorite samples has been lost through the eons. "The small amount of argon loss that has apparently taken place in these meteorites is remarkable. Any way we look at it, these rocks have been cold for a very long time," says Shuster. Their calculations suggest that the Martian surface has been in deep-freeze for most of the last four billion years.

"The temperature histories of these two planets are truly different. On Earth, you couldn't find a single rock that has been below even room temperature for that long," says Shuster. The ALH84001 meteorite, in fact, couldn't have been above freezing for more than a million years during the last 3.5 billion years of history.

"Our research doesn't mean that there weren't pockets of isolated water in geothermal springs for long periods of time, but suggests instead that there haven't been large areas of free-standing water for four billion years.

"Our results seem to imply that surface features indicating the presence and flow of liquid water formed over relatively short time periods," says Shuster.

On a positive note for astrobiology, however, Weiss says that the new study does nothing to disprove the theory of "panspermia," which holds that life can jump from one planet to another by meteorites. Weiss and his supervising professor at Caltech, Joe Kirschvink (the Van Wingen Professor of Geobiology), several years ago showed that microbes could indeed have traveled from Mars to Earth in the hairline fractures of ALH84001 without having been destroyed by heat. In particular, the fact that the nakhlites have never been heated above about 200 degrees Fahrenheit means that they were not heat-sterilized during ejection from Mars and transfer to Earth.

The title of the new paper is "Martian Surface Paleotemperatures from Thermochronology of Meteorites."

 

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Robert Tindol
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First Planet Under Three Suns Is Discovered

PASADENA, Calif.—An extrasolar planet under three suns has been discovered in the constellation Cygnus by a planetary scientist at the California Institute of Technology using the 10-meter Keck I telescope in Hawaii. The planet is slightly larger than Jupiter and, given that it has to contend with the gravitational pull of three bodies, promises to seriously challenge our current understanding of how planets are formed.

In the July 14 issue of Nature, Maciej Konacki, a senior postdoctoral scholar in planetary science at Caltech, reports on the discovery of the Jupiter-class planet orbiting the main star of the close-triple-star system known as HD 188753. The three stars are about 149 light-years from Earth and are about as close to one another as the distance between the sun and Saturn.

In other words, a viewer there would see three bright suns in the sky. In fact, the sun that the planet orbits would be a very large object in the sky indeed, given that the planet's "year" is only three and a half days long. And it would be yellow, because the main star of HD 188753 is very similar to our own sun. The larger of the other two suns would be orange, and the smaller red.

Konacki refers to the new type of planet as "Tatooine planets," because of the similarity to Luke Skywalker's view of his home planet's sky in the first Star Wars movie.

"The environment in which this planet exists is quite spectacular," says Konacki. "With three suns, the sky view must be out of this world-literally and figuratively."

However, Konacki adds that the fact that a planet can even exist in a multiple-star system is amazing in itself. Binary and multiple stars are quite common in the solar neigborhood, and in fact outnumber single stars by some 20 percent.

Researchers have found most of the extrasolar planets discovered so far by using a precision velocity technique that is easier to employ on studies of single stars. Experts generally avoided close-binary and close-multiple stars because the existing planet detection techniques fail for such complicated systems, and also because theories of solar-system formation suggested that planets were very unlikely to form in such environments.

Konacki's breakthrough was made possible by his development of a novel method that allows him to precisely measure velocities of all members of close-binary and close-multiple-star systems. He used the technique for a search for extrasolar planets in such systems with the Keck I telescope. The planet in the HD 188753 system is the first one from this survey.

"If we believe that the same basic processes lead to the formation of planets around single stars and components of multiple stellar systems, then such processes should be equally feasible, regardless of the presence of stellar companions," Konacki says. "Planets from complicated stellar systems will put our theories of planet formation to a strict test."

Scientists in 1995 discovered the first "hot Jupiter"-in other words, an extrasolar gas-giant planet with an orbital period of three to nine days. Today, more than 20 such planets are known to orbit other stars. These planets are believed to form in a disk of gas and condensed matter at or beyond three astronomical units (three times the 93-million-mile distance between the sun and Earth).

A sufficient amount of solid material exists at three astronomical units to produce a core capable of capturing enough gas to form a giant planet. After formation, these planets are believed to migrate inward to their present very close orbits.

If the parent star is orbited by a close stellar companion, then its gravitational pull can significantly truncate a protoplanetary disk around the main star. In the case of HD 188753, the two stellar companions would truncate the disk around the main star to a radius of only 1.3 astronomical units, leaving no space for a planet to form.

"How that planet formed in such a complicated setting is very puzzling. I believe there is yet much to be learned about how giant planets are formed," says Konacki.

The research was funded by NASA.

 

 

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Robert Tindol
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Research on Sumatran Earthquakes Uncovers New Mysteries about Workings of Earth

PASADENA, Calif.--The Sumatra-Andaman earthquake of December 26 was an unmitigated human disaster. But three new papers by an international group of experts show that the huge data return could help scientists better understand extremely large earthquakes and the disastrous tsunamis that can be associated with them.

Appearing in a themed issue of this week's journal Science, the three papers are all co-authored by California Institute of Technology seismologists. The papers describe in unprecedented detail the rupture process of the magnitude-9 earthquake, the nature of the faulting, and the global oscillations that resulted when the earthquake "delivered a hammer blow to our planet." The work also shows evidence that the odd sequence of ground motions in the Andaman Islands will motivate geophysicists to further investigate the physical processes involved in earthquakes.

"For the first time it is possible to do a thorough seismological study of a magnitude-9 earthquake," says Hiroo Kanamori, who is the Smits Professor of Geophysics at Caltech and a co-author of all three papers. "Since the occurrence of similar great earthquakes in the 1960s, seismology has made good progress in instrumentation, theory, and computational methods, all of which allowed us to embark on a thorough study of this event."

"The analyses show that the Global Seismic Network, which was specifically designed to record such large earthquakes, performed exactly according to design standards," adds Jeroen Tromp, who is McMillan Professor of Geophysics and director of the Caltech Seismology Lab. "The network enables a broadband analysis of the rupture process, which means that there is considerable information over a broad range of wave frequencies, allowing us to study the earthquake in great detail.."

In fact, Kanamori points out, the data have already motivated tsunami experts to investigate how tsunamis are generated by seismic deformation. In the past, seismic deformation was treated as instantaneous uplift of the sea floor, but because of the extremely long rupture length (1200 km), slow deformation, and the large horizontal displacements as well as vertical deformation, the Sumatra-Andaman earthquake forced tsunami experts to rethink their traditional approach. Experts and public officials are now incorporating these details into modeling so that they can more effectively mitigate the human disaster of future tsunamis.

Another oddity contained in the data is the rate at which the ground moved in the Andaman Islands. Following the rapid seismic rupture, significant slip even larger than the co-seismic slip (in other words, the slip that occurred during the actual earthquake) continued beneath the islands over the next few days.

"We have never seen this kind of behavior," says Kanamori. "If slip can happen over a few days following the rapid co-seismic slip, then important hitherto unknown deformational processes in the Earth's crust must have been involved; this will be the subject of future investigations."

As for the "ringing" of Earth for literally weeks after the initial shock, the scientists say that the information will provide new insights into the planet's interior composition, mineralogy, and dynamics. In addition, the long-period free oscillations of such a large earthquake provide information on the earthquake itself.

The first of the papers is "The Great Sumatra-Andaman Earthquake of 26 December 2004. " In addition to Kanamori, the other authors are Thorne Lay (the lead author) and Steven Ward of UC Santa Cruz; Charles Ammon of Penn State; Meredith Nettles and Goan Estrom of Harvard; Richard Aster and Susan Bilek of the New Mexico Institute of Mining and Technology; Susan Beck of the University of Arizona; Michael Brudzinski of the University of Wisconsin and Miami University; Rhett Butler of the IRIS Consortium; Heather DeShon of the University of Wisconsin; Kenji Satake of the Geological Survey of Japan; and Stuart Sipkin of the US Geological Survey's National Earthquake Information Center.

The second paper is "Rupture Process of the 2004 Sumatra-Andaman Earthquake." The Caltech co-authors are Ji Chen, Sidao Ni, Vala Hjorleifsdottir, Hiroo Kanamori, and Donald Helmberger, the Smits Family Professor of Geological and Planetary Sciences.

The other authors are Charles Ammon (the lead author) of Penn State; David Robinson and Shamita Das of the University of Oxford; Thorne Lay of UC Santa Cruz; Hong-Kie Thio and Gene Ichinose of URS Corporation; Jascha Polet of the Institute for Crustal Studies; and David Wald of the National Earthquake Information Center.

The third paper is "Earth's Free Oscillations Excited by the 26 December 2004 Sumatra-Andaman Earthquake," of which Jeffrey Park of Yale University is lead author. The Caltech coauthors are Teh-Ruh Alex Song, Jeroen Tromp, and Hiroo Kanamori. The other authors are Emile Okal and Seth Stein of Northwestern University; Genevieve Roult and Eric Clevede of the Institute de Physique du Globe, Paris; Gabi Laske, Peter Davis, and Jon Berger of the Scripps Institute of Oceanography; Carla Braitenberg of the University of Trieste; Michel Van Camp of the Royal Observatory of Belgium; Xiang'e Lei, Heping Sun, and Houze Xu of the Chinese Academy of Sciences' Institute of Geodesy and Geophysics; and Severine Rosat of the National Astronomical Observatory of Japan.

The second paper contains web references to three animations that help to illustrate various aspects of this great earthquake:

http://www.gps.caltech.edu/~vala/sumatra_velocity_global.mpeg

Global movie of the vertical velocity wave field. The computation includes periods of 20 seconds and longer and shows a total duration of 3 hours. The largest amplitudes seen in this movie are the Rayleigh waves traveling around the globe. Global seismic stations are shown as yellow triangles.

http://www.gps.caltech.edu/~vala/sumatra_velocity_local.mpeg

Animation of the vertical velocity wave field in the source region. The computation includes periods of 12 seconds and longer with a total duration of about 13 minutes. As the rupture front propagates northward the wave-field gets compressed and amplified in the north and drawn out to the south. The radiation from patches of large slip shows up as circles that are offset from each other due to the rupture propagation (a Doppler-like effect).

http://www.gps.caltech.edu/~vala/sumatra_displacement_local.mpeg

Evolution of uplift and subsidence above the megathrust with time. The duration of the rupture is 550 seconds. This movie shows the history of the uplift at each point around the fault and, as a result, the dynamic part of the motion is visible (as wiggling contour lines). The simulation includes periods of 12 s and longer. The final frame of the movie shows the static field.

All animations were produced by Seismo Lab graduate student Vala Hjorleifsdottir with the assistance of Santiago Lombeyda at Caltech's Center for Advanced Computing Research. The simulations were performed on 150 nodes of Caltech's Division of Geological & Planetary Sciences' Dell cluster.

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Robert Tindol
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The Science behind the Aceh Earthquake

PASADENA, Calif. - Kerry Sieh, the Robert P. Sharp Professor of Geology at the California Institute of Technology and a member of Caltech's Tectonics Observatory, has conducted extensive research on both the Sumatran fault and the Sumatran subduction zone. Below, Sieh provides scientific background and context for the December 26, 2004 earthquake that struck Aceh, Indonesia.

The earthquake that struck northern Sumatra on December 26, 2004, was the world's largest earthquake since the great (magnitude 9.2) Alaskan earthquake of 1964. The great displacements of the sea floor associated with the earthquake produced exceptionally large tsunami waves that spread death and destruction throughout the Bay of Bengal, from Northern Sumatra to Thailand, Sri Lanka, and India.

The earthquake originated along the boundary between the Indian/Australian and Eurasian tectonic plates, which arcs 5,500 kilometers (3,400 miles) from Myanmar past Sumatra and Java toward Australia see Figure 1. Near Sumatra, the Indian/Australian plate is moving north-northeast at about 60 millimeters (2.4 in.) per year with respect to Southeast Asia. The plates meet 5 kilometers (3 miles) beneath the sea at the Sumatran Trench, on the floor of the Indian Ocean Figure 2. The trench runs roughly parallel to the western coast of Sumatra, about 200 kilometers (125 miles) offshore. At the trench, the Indian/Australian plate is being subducted; that is, it is diving into the earth's interior and being overridden by Southeast Asia. The contact between the two plates is an earthquake fault, sometimes called a "megathrust." Figure 3 The two plates do not glide smoothly past each other along the megathrust but move in "stick-slip" fashion. This means that the megathrust remains locked for centuries, and then slips suddenly a few meters, generating a large earthquake.

History reveals that the subduction megathrust does not rupture all at once along the entire 5,500-kilometer plate boundary. The U.S. Geological Survey reports that the rupture began just north of Simeulue Island Figure 4. From the analysis of seismograms, Caltech seismologist Chen Ji has found that from this origin point, the major rupture propagated northward about 400 kilometers (249 miles) along the megathrust at about two kilometers per second. By contrast, the extent of major aftershocks suggests that the rupture extended about a thousand kilometers (620 miles) northward to the vicinity of the Andaman Islands. During the rupture, the plate on which Sumatra and the Andaman Islands sit lurched many meters westward over the Indian plate.

The section of the subduction megathrust that runs from Myanmar southward across the Andaman Sea, then southeastward off the west coast of Sumatra, has produced many large and destructive earthquakes in the past two centuries Figure 5. In 1833, rupture of a long segment offshore central Sumatra produced an earthquake of about magnitude 8.7 and attendant large tsunamis. In 1861, a section just north of the equator produced a magnitude 8.5 earthquake and large tsunamis. Other destructive historical earthquakes and tsunamis have been smaller. A segment to the north of the Nicobar Islands ruptured in 1881, generating an earthquake with an estimated magnitude of 7.9. A short segment farther to the south, under the Batu Islands, ruptured in 1935 (magnitude 7.7). A segment under the Enganno Island ruptured in 2000 (magnitude 7.8), and a magnitude 7.4 precursor to the recent earthquake occurred in late 2002, under Simeulue Island.

This recent earthquake was generated by the seismic rupture of only the northernmost portion of the Sumatran section of the megathrust. Therefore, the fact that most of the other part of the section has generated few great earthquakes in more than a hundred years is worrisome. Paleoseismic research has shown that seismic ruptures like the one in 1833, for example, recur about every two centuries. Thus, other parts within the section of this fault should be considered dangerous over the next few decades.

During rupture of a subduction megathrust, the portion of Southeast Asia that overlies the megathrust jumps westward (toward the trench) by several meters, and upward by 1-3 meters (3-10 feet). This raises the overlying ocean, so that there is briefly a "hill" of water about 1-3 meters high overlying the rupture. The flow of water downward from this hill triggers a series of broad ocean waves that are capable of traversing the entire Bay of Bengal. When the waves reach shallow water they slow down and increase greatly in height--up to 10 meters (32 feet) or so in the case of the December 26 earthquake--and thus are capable of inundating low-lying coastal areas.

Although the tsunami waves subside in a short period of time, some coastal areas east of the megathrust sink by a meter or so, leading to permanent swamping of previously dry, habitable ground. Islands above the megathrust rise 1 to 3 meters, so that shallow coral reefs emerge from the sea. Such long-term changes resulting from the December 26 earthquake will be mapped in the next few months by Indonesian geologists and their colleagues.

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More Stormy Weather on Titan

PASADENA, Calif.— Titan, it turns out, may be a very stormy place. In 2001, a group of astronomers led by Henry Roe, now a postdoctoral scholar at the California Institute of Technology, discovered methane clouds near the south pole of Saturn's largest moon, resolving a debate about whether such clouds exist amid the haze of its atmosphere.

Now Roe and his colleagues have found similar atmospheric disturbances at Titan's temperate mid-latitudes, about halfway between the equator and the poles. In a bit of ironic timing, the team made its discovery using two ground-based observatories, the Gemini North and Keck 2 telescopes on Mauna Kea, in Hawaii, in the months before the Cassini spacecraft arrived at Saturn and Titan. The work will appear in the January 1, 2005, issue of the Astrophysical Journal.

"We were fortunate to catch these new mid-latitude clouds when they first appeared in late 2003 and early 2004," says Roe, who is a National Science Foundation Astronomy and Astrophysics Postdoctoral Scholar at Caltech. Much of the credit goes to the resolution and sensitivity of the two ground-based telescopes and their use of adaptive optics, in which a flexible mirror rapidly compensates for the distortions caused by turbulence in the Earth's atmosphere. These distortions are what cause the well-known twinkling of the stars. Using adaptive optics, details as small as 300 kilometers across can be distinguished despite the enormous distance of Titan (1.3 billion kilometers). That's equivalent to reading an automobile license plate from 100 kilometers away.

Still to be determined, though, is the cause of the clouds. According to Chad Trujillo, a former Caltech postdoctoral scholar and now a scientist at the Gemini Observatory, Titan's weather patterns can be stable for many months, with only occasional bursts of unusual activity like these recently discovered atmospheric features.

Like Earth, Titan's atmosphere is mostly nitrogen. Unlike Earth, Titan is inhospitable to life due to the lack of atmospheric oxygen and to its extremely cold surface temperatures (-297 degrees Fahrenheit). Along with nitrogen, Titan's atmosphere also contains a significant amount of methane, which may be the cause of the mid-latitude clouds.

Conditions on Earth allow water to exist in liquid, solid, or vapor states, depending on localized temperatures and pressures. The phase changes of water between these states are an important factor in the formation of weather in our atmosphere. But on Titan, methane rules. The moon's atmosphere is so cold that any water is frozen solid, but methane can move between liquid, solid, and gaseous states. This leads to a methane meteorological cycle on Titan that is similar to the water-based weather cycle on Earth.

While the previously discovered south polar clouds are thought to be a result of solar surface heating, the new mid-latitude clouds cannot be formed by the same mechanism. One possible explanation for the new clouds is a seasonal shift in the global winds. More likely, says Roe, surface activity might be disturbing the atmosphere at the mid-latitude location. Geysers of methane slush may be brewing up from below, or a warm spot on Titan's surface may be heating the atmosphere. Cryovolcanism--volcanic activity that spews an icy mix of chemicals--is another mechanism that could cause disturbances. Hints about what is happening on this frigid world could be obtained as the Huygens probe, which will be released from Cassini on Christmas day, drops through Titan's atmosphere in January 2005.

If the clouds are being caused by these geological conditions, says Roe, they should stay at the observed 40-degree latitude and repeatedly occur above the same surface feature or features. Meanwhile, if a seasonal shift in the winds is forming the clouds then their locations should move northward as Titan's season progresses into southern summer. "Continued observations with the Gemini and Keck telescopes will easily distinguish between these two scenarios," says Roe.

The Gemini observatory is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation, involving the National Optical Astronomy Observatory, AURA, and the NSF as the U.S. partner. The W.M. Keck Observatory is operated by the California Association for Research in Astronomy, a scientific partnership between the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

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Observing the Roiling Earth

PASADENA, Calif. - In the 1960s the theory of plate tectonics rocked geology's world by determining that the first 60 miles or so of our planet--the lithosphere--is divided into about a dozen rigid plates that crawl along by centimeters each year. Most manifestations of the earth's dynamics, earthquakes and volcanoes for example, occur along the boundaries of these plates.

As a model, the theory of plate tectonics continues to serve us well, says Jean-Philippe Avouac, a professor of geology at the California Institute of Technology. But while plate tectonics provides a powerful description of the large-scale deformation of the earth's lithosphere over millions of years, it doesn't explain the physical forces that drive the movements of the plates. Also, contrary to the theory, it's now known that plates are not perfectly rigid and that plate boundaries sometimes form broad fault zones with diffuse seismicity.

Now, thanks to a $13,254,000 grant from the Gordon and Betty Moore Foundation, Caltech has established the Tectonic Observatory, under the direction of Avouac, with the ultimate goal, he says, of "providing a new view of how and why the earth's crust is deforming over timescales ranging from a few tens of seconds, the typical duration of an earthquake, to several tens of million of years."

But it's not the only goal. "Most of the outstanding questions in earth science concern processes that take place at the boundaries of the earth's tectonic plates," says Avouac, so the observatory's scientific efforts will be centered around major field studies at a few key plate boundaries in western North America, Sumatra, Central America, and Taiwan, with the goal of answering a number of questions, including:

--Tectonic plates move gradually when viewed on large timescales, but then sometimes undergo sharp "jerks" in speed and direction. What's the cause?

--Because earthquakes can be damaging events to humans, it's important to know: what physical parameters control their timing, location, and size?

--Subduction zones, where oceanic plates sink into the earth's mantle, are needed to accommodate and perhaps drive plate motion. How do these subduction zones originate and grow?

"We plan to take advantage of a number of new technologies that will allow us to measure deformation of the earth's crust and image the earth's interior with unprecedented accuracy," says Avouac. The bulk of the grant will be spent on these new technologies, along with acquiring data that will be used to observe and model the boundary zones. In addition to seismometers, other equipment and data that's needed will include space-based GPS, which will allow geologists to measure the relative velocity of two points on the earth's surface to within a few millimeters each year; satellite images to map displacements of broad areas of the ground's surface over time; geochemical fingerprinting methods to analyze and date rocks that have been brought to the surface by volcanic eruptions or erosion, thus helping to characterize the composition of the earth far below; and of course, massive computation to analyze all the data, along with advanced computational techniques, "to allow us to develop models at the scale of the global earth," says Avouac.

"The breakthroughs we will achieve will probably result from the interactions among the various disciplines that will contribute to the project," he says. "We've already begun our effort, for example, by imaging and monitoring seismic activity and crustal deformation along a major subduction zone in Mexico. As I speak, geologists are in the field and continuing to install what will be a total of 50 seismometers."

Few institutions are capable of mounting this kind of sustained, diverse effort on a single plate boundary, he says, or of mining data from multiple disciplines to create dynamic models. "That's what Caltech is capable of doing," says Avouac. "We hope to breed a new generation of earth scientist. The Tectonics Observatory will offer students an exceptional environment with access to all of the modern techniques and analytical tools in our field, along with the possibility of interacting with a group of faculty with an incredibly diversified expertise."

The Gordon and Betty Moore Foundation was established in September 2000 by Intel cofounder Gordon Moore and his wife, Betty. The foundation funds projects that will measurably improve the quality of life by creating positive outcomes for future generations. Grantmaking is concentrated in initiatives that support the Foundation's principal areas of concern: environmental conservation, science, higher education, and the San Francisco Bay Area.

MEDIA CONTACT: Mark Wheeler (626) 395-8733 wheel@caltech.edu

Visit the Caltech media relations web site: http://pr.caltech.edu/media

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NSF Awards $6.75 Million to Caltech for Geodynamics Computational Facility

PASADENA, Calif.--The National Science Foundation has awarded $6.75 million to the California Institute of Technology to house the central activities of a major new community-based, software engineering effort to revolutionize scientific computing in geophysics. The NSF initiative, which will involve at least 24 other American universities and research institutions and four foreign affiliates, is intended to allow scientists studying such fields as seismology, plate tectonics, volcanism, and geomagnetism to take full advantage of recent advances and extraordinary opportunities available in scientific computation.

According to founding director Michael Gurnis, a professor of geophysics at Caltech, the center will focus on developing advanced software that will enable individual Earth scientists to produce more realistic simulations for studying natural phenomena, and also for the analysis and integration of data. The Computational Infrastructure for Geodynamics (CIG) will initially be located on the main campus in central Pasadena, and later at the recently acquired St. Luke property in northeast Pasadena.

"CIG will enable scientific progress in several areas of geophysics," Gurnis says. "The frontier has moved into multiscale and multiphysics problems in which investigators now want to use simulation software for data interpretation, data assimilation, and hypothesis testing."

Robin Reichlin, program director in NSF's division of Earth sciences, says, "The CIG will revolutionize computational geodynamics by developing anddocumenting state-of-the-art, modular codes that will benefit a cross-section of Earth scientists. CIG products will be flexible enough to be run on supercomputing platforms or desktop computers used in classrooms, helping to educate the next generation of computational Earth scientists."

According to Gurnis, "Our science is now moving into a new era as the United States deploys an unprecedented array of instrumentation to image the planet's interior and sense the slight tectonic motions of the surface with EarthScope. CIG will allow researchers to model and interpret the tidal wave of data from EarthScope and other initiatives. Scientific computing has become an essential component in earth science research and CIG will allow the national community to advance software in lock step with the huge growth in geophysical data."

According to Louise Kellogg, professor of geophysics at the University of California, Davis, "CIG will be a catalyst for collaboration among earth scientists and computer scientists. By developing new methods and taking advantage of advances in software engineering and computer hardware, these communities will be able to work towards solving some of the major scientific questions in Earth sciences."

CIG will consist of a core team of software architects and engineers dedicated to creating new products. In addition, the center will support a visitor's program open to the international Earth science community.

Gurnis believes "that the special attribute of CIG will be the infrastructure allowing an immensely talented and creative community of scientists--the US community of computational geophysicists--to collaborate in the development of a new generation of computational software that will allow us to solve previously intractable problems."

Marc Spiegelman, an expert in magma migration at Columbia University, adds, "The CIG promises a new era in both individual and collaborative Earth science that makes advances in computational science and modern hardware accessible to a much larger community of scientists. CIG also marks a new level of collaboration between Earth scientists and computational scientists. I am very impressed with the computational scientists already involved in this project and it gives me confidence that exciting and important new science and technology will result from the CIG."

The focus of the software development will concentrate on several areas of Earth science:

< Better understanding of mantle dynamics. Earth's mantle and its convection are known to be responsible for plate tectonics and continental drift, but the processes are poorly understood.

< Better understanding of magma dynamics and geochemical transport. The dynamics and evolution of Earth's interior can be inferred from the chemistry of the materials erupted from the mantle, but the picture is so complicated that there are still many open questions, including how melted and solid materials are distributed and interact to affect the geochemical evolution of the planet.

< Crustal and lithospheric dynamics on million-year timescales. The crust we live on undergoes deformations over long timescales, and better modeling could lead to increased understanding of how erosion from climate change and crustal changes are related.

< Crustal dynamics on earthquake timescales. This area is of tremendous societal importance because advances in understanding how stress relates to the triggering of earthquakes and aftershocks could lead to better knowledge of earthquake hazard.

< Seismic wave propagation. The data already coming from existing instruments will soon be augmented by data from the EarthScope project, which will call for better computational tools for analysis and modeling.

< The geodynamo. Progress in understanding Earth's magnetic field will require extensive numerical investigations.

The long-term goal of the new center will be to develop a flexible infrastructure for modeling. According to Gurnis, the collaborators have set a priority of designing within the first 18 months of operation a "coherent functionality" of geodynamics.

"We officially started on September 1, and the activity will grow over the next several years," Gurnis says.

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