Life rebounded quickly after collision 65 million years ago that wiped out dinosaurs

Though the dinosaurs fared poorly in the comet or meteor impact that destroyed two-thirds of all living species 65 million years ago, new evidence shows that various other forms of life rebounded from the catastrophe in a remarkably short period of time.

In the March 9 issue of the journal Science, a team of geochemists reports that life was indeed virtually wiped out for a period of time, but then reappeared just as abruptly only 10,000 years after the initial collision. Further, the evidence shows that the extinctions 65 million years ago, which mark the geologic time known as the Cretaceous-Tertiary (K-T) boundary, were most likely caused by a single catastrophic impact.

"There's been a longstanding debate whether the mass extinctions at the K-T boundary were caused by a single impact or maybe a swarm of millions of comets," says lead author Sujoy Mukhopadhyay, a graduate student at Caltech. "In addition, figuring out the duration of the extinction event and how long it took life to recover has been a difficult problem."

To address both questions, Mukhopadhyay and his colleagues measured the amount of cosmic dust in the sediments of an ancient sea bed which is now exposed on land about 100 miles north of Rome. In particular they focused on a two-centimeter-thick clay deposit that previously had been dated to about 65 million years ago. The base of this clay deposit corresponds to the date of the extinction event.

The clay deposit lies above a layer of limestone sediments, which are essentially the skeletons of microscopic sea life that settled at the bottom of the ancient sea. The limestone deposit also contains a certain percentage of clay particles, which result from erosion on the continents. Finally, mixed in the sediments is extraterrestrial dust that landed in Earth's oceans and then settled out. This dust carries a high concentration of helium-3 (3He), a rare isotope of helium that is depleted on Earth but highly enriched in cosmic matter.

The lower limestone layer abruptly ends at roughly 65 million years, since the organisms in the ocean were suddenly wiped out by the impact event. Thus, the layer immediately above the limestone contains nothing but the clay deposits and extraterrestrial dust that continued to settle at the bottom of the ancient sea. Immediately above the two-centimeter clay deposit is another layer of limestone deposits from microorganisms of the sea that eventually rebounded after the catastrophe.

In this study, the researchers measured the amount of 3He in the sediments to learn about the K-T extinction. They reasoned that a gigantic impact would not change the amount of 3He in the clay deposit. This is because large impacting bodies are mostly vaporized upon impact and release all their helium into the atmosphere. Because helium is a light element, it is not bound to Earth and tends to drift away into space. Therefore, even if a huge amount were brought to Earth by a large impact, the 3He would soon disappear and not show up in the sedimentary layers.

In contrast, 3He brought to Earth by extraterrestrial dust tends to stay trapped in the dust and not be lost to space, says Kenneth Farley, professor of geochemistry at Caltech and coauthor of the paper. So 3He found in the limestone and the clay deposits came from space in the form of dust.

Based on the 3He record obtained from the limestones, the researchers eliminated the possibility that a string of comets had caused the K-T extinctions. Comets are inherently dusty, so a string of them hitting Earth would have brought along a huge amount of new dust, thereby increasing the amount of 3He in the lower limestone deposit.

But the Italian sediment showed a steady concentration of 3He until the time of the impact, eliminating the possibility of a comet swarm. In fact, the researchers found no evidence for periodic comet showers, which have been suggested as the cause of mass extinction events on Earth.

Mukhopadhyay and his colleagues reason that because the "rain-rate" of the extraterrestrial dust from space did not change across the K-T boundary, the 3He concentration in the clay is proportional to the total depositional time of the clay. "It's been difficult to measure the time it took for this two-centimeter clay layer to be deposited," says Farley.

The researchers conclude that the two-centimeter clay layer was deposited in approximately 10,000 years. Then, very quickly, the tiny creatures that create limestone deposits reemerged and again began leaving their corpses on the ocean bed. The implication is that life can get started again very quickly, Farley says.

Thus the study answers two major questions about the event that led to the extinction of the dinosaurs, says Mukhopadhyay. In addition to Mukhopadhyay and Farley, the paper is also authored by Alessandro Montanari of the Geological Observatory in Apiro, Italy.

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Robert Tindol
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Stevenson Receives Feynman Prize for Excellence in Teaching

PASADENA, Ca.— "One hopes that students are being taught to think and not just grind through lots of homework," says Caltech's David Stevenson about the importance of teaching. In recognition of his passion for undergraduate education, Stevenson has been awarded this year's Richard P. Feynman Prize for Excellence in Teaching.

The George Van Osdol Professor of Planetary Sciences, Stevenson was honored by a selection committee composed of faculty and students for modifying the existing Geology 1 class into a new elective course within the core curriculum. "I was challenged," says Stevenson, "by the difficulty of constructing a course that would be attractive to a wide range of students, yet not be too conventional–not just a set of lectures. In practice, it's hard to avoid routine approaches; you want students to learn to think, which means that the problems in the exams, homework, and projects should not be merely routine applications of standard book work." The selection committee cited Stevenson's success in avoiding such routine, noting the increase in the class's enrollment, from 20 students at its start to 165 this year.

The Feynman Prize is made possible by the generosity of an endowment from Ione and Robert E. Paradise, along with additional contributions from Mr. and Mrs. William H. Hurt. It is named in honor of the late Caltech Nobel Laureate and popular science author, who was lauded for his innovative classroom lectures on physics. The prize is given each year to a Caltech professor who demonstrates exceptional ability, creativity, and innovation in both laboratory and classroom instruction.

The selection committee cited Stevenson's "lucid and enthusiastic" teaching style, along with his ability to bring together concepts from evolution, biology, and chemistry, thus making Geology 1 "unlike any other course of its kind in the world." Stevenson also incorporated the use of small group projects, each led by an individual professor, along with field trips to give students the opportunity of first-hand observation. The result, the committee noted, was to create "a lasting impression of how geology research is done, how our Earth was created, and how our environment evolves."

Stevenson notes that teaching is also helpful to him. "Teaching helps the teacher as well as the student. This is especially true of people who are more theoretically inclined in their research"—(Stevenson doesn't have a lab)—"because that kind of research is helped by looking at things with a fresh approach."

He admits, too, that teaching can also be fun: "You can think of different applications of the ideas, how it relates to current research, and how it can be valuable to a non-expert."

Stevenson's own research efforts concerning the origin, evolution, and structure of planets, including Earth, are noteworthy as well. In 1998, the American Geophysical Union awarded him its Harry H. Hess Medal for outstanding achievements in the research of the constitution and evolution of Earth and its sister planets. In addition, in 1993 Stevenson was elected as a Fellow of the Royal Society, the United Kingdom's national academy of science, in recognition of his scientific excellence and work of distinction.

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New planets still being createdIn our stellar neighborhood, study shows

In a study that strengthens the likelihood that solar systems like our own are still being formed, an international team of scientists is reporting today that three young stars in the sun's neighborhood have the raw materials necessary for the formation of Jupiter-sized planets.

Data obtained from the European Space Agency's Infrared Space Observatory (ISO) indicate for the first time that molecular hydrogen is present in the debris disks around young nearby stars. The results are important because experts have long thought that primordial hydrogen—the central building block of gas giants such as Jupiter and Saturn—is no longer present in sufficient quantities in the sun's stellar vicinity to form new planets.

The paper appears in the January 4 issue of the journal Nature.

"We looked at only three stars, but the results could indicate that it's easier to make Jupiter-sized planets than previously thought," said Geoffrey Blake, professor of cosmochemistry at the California Institute of Technology and corresponding author of the study. "There are over 100 candidate debris disks within about 200 light-years of the sun, and our work suggests that many of these systems may still be capable of making planets."

The abundance of Jupiter-sized planets is good news, though indirectly, in the search for extraterrestrial life. A gas giant such as Jupiter, may not be particularly hospitable for the formation of life, but experts think the mere presence of such huge bodies in the outer reaches of a solar system protects smaller rocky planets like Earth from catastrophic comet and meteor impacts. A Jupiter-sized planet possesses a gravitational field sufficient to kick primordial debris into the farthest reaches of the solar system, as Jupiter has presumably done by sending perhaps billions of comets into the Oort Cloud beyond the orbit of Pluto and safely away from Earth.

If comets and meteors were not ejected by gas giants, Blake said, life on Earth and any other Earth-like planets in the universe could periodically be "sterilized" by impacts.

"A comet the size of Hale-Bopp, for example, would vaporize much of Earth's oceans if it hit there," Blake said. "The impact from a 500 km object (about ten times the size of Hale-Bopp) could create nearly 100 atmospheres of rock vapor, the heat from which can evaporate all of the Earth's oceans."

The researchers did not directly detect any planets in the study, but nonetheless found that molecular hydrogen was abundant in all three disks they targeted. In the disk surrounding Beta Pictoris, a Southern Hemisphere star that formed about 20 million years ago approximately 60 light-years from Earth, the team found evidence that hydrogen is present in a quantity at least one-fifth the mass of Jupiter, or about four Neptune's worth of material.

The debris disk of the star 49 Ceti, which is visible near the celestial equator in the constellation Cetus, was found to contain hydrogen in a quantity at least 40 percent of the mass of Jupiter. Saturn's mass is just under a third that of Jupiter. 49 Ceti, which is about 10 million years old, is about 200 light-years from Earth.

Best of all was a 10-million-year-old Southern Hemisphere star about 260 light-years away that goes by the rather unpoetic name HD135344. That star's surrounding debris disk was found to contain the equivalent of at least six Jupiter masses of molecular hydrogen.

"There may not be enough material to form Jupiters around Beta Pictoris or 49 Ceti, but our figures establish a lower limit that is well within the gas-giant planet range, which means we definitely detected a fair amount of gas. And there could be more," Blake said. "Around HD135344, there's at least enough material to make six Jupiters."

Not only does the study reveal that there is still sufficient molecular hydrogen to make gas giants but also that planetary formation is not limited to a narrow time frame in the early history of a star, as previously thought. Because molecular hydrogen is quite difficult to detect from ground-based observatories, experts have relied on measurements of the more easily detectable carbon monoxide (CO) to model the gas dynamics of developing solar systems.

But because results showed that CO tends to dissipate quite rapidly in the early history of debris disks, researchers assumed that molecular hydrogen was likewise absent. Further, the presumed lack of hydrogen limited the time that Jupiter-sized planets could form. However, the new study, coupled with recent theoretical models, shows that CO is not a particularly good tracer of the total gas mass surrounding a new star.

Blake said the study opens new doors to the understanding of planetary growth processes around sun-like stars. He and his colleagues anticipate further progress when the Space Infrared Telescope Facility (SIRTF) and the Stratospheric Observatory for Infrared Astronomy (SOFIA) are launched in 2002. SIRTF, which will have its science headquarters at Caltech, alone could detect literally hundreds of stars that still contain enough primordial hydrogen in their debris disks to form Jupiter-sized planets.

The other authors of the paper are professor of astronomy Ewine F. van Dishoeck and Wing-Fai Thi (the study's lead author), both of the Leiden University in the Netherlands; Jochen Horn and professor Eric Becklin, both of the UCLA Department of Physics and Astronomy; Anneila Sargent, professor of astronomy at Caltech; Mario van den Ancker of the Harvard-Smithsonian Center for Astrophysics; and Antonella Natta of the Osservatorio Astrofisico di Arcetri in Firenze, Italy.

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New results on Martian meteorite support hypothesisthat life can jump between planets

According to one version of the "panspermia" theory, life on Earth could originally have arrived here by way of meteorites from Mars, where conditions early in the history of the solar system are thought to have been more favorable for the creation of life from nonliving ingredients. The only problem has been how a meteorite could get blasted off of Mars without frying any microbial life hitching a ride.

But new research on the celebrated Martian meteorite ALH84001 shows that the rock never got hotter than 105 degrees Fahrenheit during its journey from the Red Planet to Earth, even during the impact that ejected it from Mars, or while plunging through Earth's atmosphere before landing on Antarctic ice thousands of years ago.

In the October 27 issue of the journal Science, Caltech graduate student Benjamin Weiss, undergraduate student Francis Macdonald, geobiology professor Joseph Kirschvink, and their collaborators at Vanderbilt and McGill universities explain results they obtained when testing several thin slices of the meteorite with a new state-of-the-art device known as an Ultra-High Resolution Scanning Superconducting Quantum Interference Device Microscope (UHRSSM). The machine, developed by Franz Baudenbacher and other researchers at Vanderbilt, is designed to detect microscopic differences in the orientation of magnetic lines in rock samples, with a sensitivity up to 10,000 times greater than existing machines.

"What's exciting about this study is that it shows the Martian meteorite made it from the surface of Mars to the surface of Earth without ever getting hot enough to destroy bacteria, or even plant seeds or fungi," says Weiss, the lead author of the Science paper. "Other studies have suggested that rocks can make it from Mars to Earth in a year, and that some living organisms can live in space for several years. So the transfer of life is quite feasible."

The meteorite ALH84001 has been the focus of numerous scientific studies in the last few years because some scientists think there is tantalizing evidence of fossilized life within the rock. The issue has never been conclusively resolved, but Weiss says the matter is not important to the present result.

"In fact, we don't think that this particular meteorite brought life here," says Weiss. "But computer simulations of ejected Martian meteorites demonstrate that about one billion tons of rocks have been brought to Earth from Mars since the two planets formed." Many of these rocks make the transit in less than one year, although ALH84001 took about 15 million years.

"The fact that at least one out of the 16 known Martian rocks made it here without heating tells us that this must be a fairly common process," says Kirschvink.

The sample the Kirschvink team worked with is about 1 mm thick and 2 cm in length and somewhat resembles the African continent, with one side containing a portion of the original surface of the meteorite. Using the UHRSSM, the team found that the sample has a highly aligned and intense magnetic field near the surface, which is to be expected because the surface reached a high temperature when it entered Earth's atmosphere.

The reason this is important is that any weakly magnetized rock will reorient its magnetization to be aligned with the local field direction after it has been heated to high temperatures and cooled. This critical temperature for any magnetic material is known as the blocking temperature. Thus, the outer surface layer of meteorite ALH84001 reached a high temperature well above the blocking temperatures of its magnetic materials, which caused the materials at the surface to realign with Earth's magnetic field.

However, the interior portions of the slice were found to have randomly oriented magnetization, which means that some of the materials inside the meteorite never reached their blocking temperatures since sometime before they left the Martian surface. Further, when the researchers gently heated another slice taken from the interior of the meteorite, they discovered that the interior of the rock started to demagnetize at temperatures as low as 40 degrees Celsius—or 105 degrees Fahrenheit—thus demonstrating that it had never been heated even to that level.

Thus, a radiation-resistant organism able to survive without energy and water for a year could have made the journey from Mars to Earth. Examples of such hardy organisms, like the bacteria bacillus subtilis and deinococcus radiodurans, are already well known.

"Realistically, we don't think any life forms more complicated than single-celled bacterial spores, very tough fungal spores, or well-protected seeds could have made it," Kirschvink says. "They would also have had to go into some kind of dormant stage."

Though the study does not directly address the issue of life in meteorites, the authors say the results eliminate a major objection to the panspermia theory—that any life form reaching Earth by meteorite would have been heat-sterilized during the violent ejection of the rock from its parent planet, or entry into the atmosphere. Prior studies have already shown that a meteorite can enter Earth's atmosphere without its inner material becoming hot.

"ALH 84001 has stimulated a remarkable amount of research to test the hypothesis that life exists elsewhere than on Earth. The present study indicates that the temperature inside the meteorite could have allowed life to persist and possibly travel to Earth from Mars," says Nobel Prize-winning biologist Baruch Blumberg, who is director of NASA's Astrobiology Institute.

The results also demonstrate that critical information could be lost if rocks brought back from Mars by a sample return mission were heat-sterilized, as has been proposed. Thermal sterilization would destroy valuable magnetic, biological, and petrological information contained in the samples.

If life ever evolved on Mars, it is likely to have jumped repeatedly to Earth over geological times. Because the reverse process—the transfer of Earth life to Mars—is dynamically much more difficult, it may be more important to instead protect any Martian biosphere from Earthly microbes.

According to Kirschvink, "The Martian biosphere, if it ever evolved, would most likely have been brought to Earth billions of years ago, and could have participated in the evolution and diversification of bacterial life here.

"So there is at least a chance that we are in part descended from Martian microbes," Kirschvink says.

The ALH84001 research was funded in part by NASA's Astrobiology Institute, an international research consortium involving academic, non-profit and NASA field centers, whose central administrative office is located at NASA's Ames Research Center in California's Silicon Valley. A group from the Jet Propulsion Laboratory in Pasadena, CA, which sponsored the Caltech research, is one of the 11 lead teams of the institute.

Contact: Robert Tindol (626) 395-3631

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Astronomers improve "cosmic yardstick" by measuringdistance to star in Gemini with Palomar Testbed Interferometer

Researchers using the testbed interferometer at Palomar Observatory have achieved the best-ever distance measurement to a type of star known as a Cepheid variable. The new results improve the "cosmic yardstick" used to infer the size and age of the universe.

In the September 28 issue of the British journal Nature, a group of astronomers from the California Institute of Technology, the Jet Propulsion Laboratory, and the Infrared Processing and Analysis Center announce that the distance to the star Zeta Geminorum in the Gemini constellation is 1,100 light years. The degree of accuracy in the measurement is about 13 percent, meaning that the star could be as close as 960 or as far away as 1,240 light-years. This represents an improvement of a factor of three over previous measurements.

The improvement is due to the use of the Palomar Testbed Interferometer, of which JPL engineer Mark Colavita is the principal investigator and codesigner. "This has been a bit of a Holy Grail in the field," says Benjamin Lane, a graduate student in Caltech's planetary science program and the lead author of the study. "The measurement of accurate distances to Cepheids is widely considered to be a principal limitation in determining the Hubble constant."

Cepheid variables for several decades have been an important link in the chain of measurements that allow astronomers to estimate the distances to the farthest objects in the universe—and ultimately, the overall size and expansion rate of the universe itself.

Cepheid variables are stars that have very predictable relationships between their absolute brightness and the frequency with which they brighten up. A Cepheid is useful for measuring distances because, if it is known how bright the star really is, then it is a simple task to measure how bright it appears on Earth and then calculate the distance.

A good analogy is a light bulb shining at an unknown distance. If we are certain that only 100-watt light bulbs brighten once a day, and we observe that the light indeed brightens once daily, then we can calculate its distance by measuring the brightness of the light reaching us and comparing it to the known absolute brightness of a 100-watt light bulb.

"Zeta Geminorum is known to grow larger and smaller," says Lane. "We already knew this because we can see the Doppler effect." In other words, astronomers can measure a slight difference in light coming from the star because the surface of the star moves toward us and away from us as the star expands and contracts.

In the Nature study, the researchers couple this information with new data collected with the Palomar Testbed Interferometer. The interferometer combines the images from two 16-inch telescope mirrors in such a way that images are as sharp as they would be if the telescope mirror were 360 feet in diameter.

Data from the interferometer showed that Zeta Geminorum went through a change in angular size of about five hundred-millionths of a degree during its 10-day cycle. "That's roughly the size of a basketball on the moon, as seen from Earth," says Colavita.

From previous Doppler measurements, the researchers already knew that the change in the star's diameter was about 4.2 million kilometers. By combining that information with the newly measured change in angular size, they were able to deduce the distance to the Cepheid.

The direct measurement of distance to Zeta Geminorum shows that the basic technique works, Lane says. "As a graduate student, it has been exciting to be at the leading edge of this field."

The Palomar Testbed Interferometer was designed and built by a team of researchers from the Jet Propulsion Laboratory in Pasadena led by Colavita and Michael Shao. Funded by NASA, the interferometer is located at the Palomar Observatory near the historic 200-inch Hale Telescope.

The device is intended as an engineering testbed for the interferometer that will soon link the 10-meter Keck Telescopes atop Mauna Kea in Hawaii.

The Keck Interferometer has been funded to find and study extrasolar planets. The Navy and the NSF are also funding the development of interferometers for astrometry and stellar astronomy.

"The current precision is a significant improvement over the previous determinations, but we expect to achieve distance measurements at the level of a few percent in the near future," says Shri Kulkarni, a professor of astronomy and planetary science at Caltech and a coauthor of the paper.

In addition to Lane and Kulkarni, the other authors are Marc Kuchner, a Caltech graduate student in astronomy; Andrew Boden of the Infrared Processing and Analysis Center (IPAC), and Michelle Creech-Eakman, a postdoctoral scholar at JPL.

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Robert Tindol
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Packard Foundation Gives Caltech $1 Million

PASADENA—In order to further a better understanding of Earth's history, the David and Lucile Packard Foundation Science Program has awarded the California Institute of Technology a $1 million grant.

This funding will help scientists investigate how microorganisms and Earth's near-surface environments have interacted over billions of years. The project, led by Dianne Newman, the Clare Boothe Luce Assistant Professor of Geobiology and Environmental Engineering Science at Caltech, will bring together investigators from a wide range of disciplines that do not traditionally overlap. They will work on a well-defined problem in the new discipline of geobiology.

The project, "The Geobiology of Anaerobic Fe(II) Oxidation: Biological, Geochemical, and Field Studies," integrates molecular microbiology with geochemistry and field geology. These scientists will try to identify chemical signatures of early life in the geologic record.

"We believe that the potential for discoveries that could come from any of the individual components alone is extraordinary, and we think that this is just the kind of challenge that the Packard Foundation had in mind when it conceived the interdisciplinary project program," said Caltech president David Baltimore.

The David and Lucile Packard Foundation was created in 1964 to support and encourage nonprofit organizations dependent on private funding and volunteer leadership. It awards grants in six main program areas: conservation; population; science, children, families, and communities; arts; and organizational effectiveness and philanthropy.

Founded in 1891, Caltech has an enrollment of some 2,000 students, and a faculty of about 275 professorial members and 130 research members. The Institute has more than 19,000 alumni. Caltech employs a staff of more than 2,100 on campus and 4,800 at JPL.

Over the years, 28 Nobel Prizes and four Crafoord Prizes have been awarded to faculty members and alumni. Forty-five Caltech faculty members and alumni have received the National Medal of Science; and eight alumni (two of whom are also trustees), two additional trustees, and one faculty member have won the National Medal of Technology. Since 1958, 13 faculty members have received the annual California Scientist of the Year award. On the Caltech faculty there are 77 fellows of the American Academy of Arts and Sciences; and on the faculty and Board of Trustees, 70 members of the National Academy of Sciences and 48 members of the National Academy of Engineering. ###

Contact: Jill Perry (626) 395-3226 jperry@caltech.edu

Visit the Caltech Media Relations Web site at: http://www.caltech.edu/~media

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East and West Antarctica once began separating but then stopped, new research shows

PASADENA—Earth was well on its way to having two Antarcticas long ago, but a tectonic separation between the eastern and western portions of the continent suddenly stopped after 17 million years of spreading, researchers say.

In the March 9 issue of Nature, lead author Steve Cande of the Scripps Institution of Oceanography, Joann Stock of Caltech, and their colleagues in Australia and Japan report that the rift between East and West Antarctica began about 43 million years ago, then ended 17 million years later, after the seafloor had spread about 180 kilometers. The researchers discovered the motion after making several cruises over a period of years in the waters off the Antarctic coast and after gathering data on the seafloor itself.

"The two pieces of Antarctica pulled apart and then stopped," says Stock, a professor of geology and geophysics at Caltech. "If it had kept on going, there would eventually have been two Antarcticas."

The primary scientific value of the study is that it answers some nagging questions about the "missing" motion in the Antarctic region. For a variety of reasons, geophysicists have had a hard time getting a handle on the precise directions and amounts of motion there, and how the motion fits into the grand scheme of global plate tectonics.

"It's like a jigsaw puzzle," Stock says. "You have to know how one piece moved relative to the other pieces to understand how it all fits together.

"A lot of the tectonic plate history for western North America, for example, depends on what happened in Antarctica. You wouldn't think so, but that's the way plate tectonic movements work."

The key to the new results was the researchers' discovery of an underwater feature off Cape Adare that they have named the Adare Trough. This trough is about 230 kilometers long and runs roughly northwest-southeast near the 170th meridian. The sharp break in the direction of the magnetic lines on either side of the trough allows the researchers to infer the ancient relative motions of the plates, and the age and shape of the trough and seafloor around it indicates the period when the spreading occurred.

Seafloor spreading in the area accounts for the "missing" motion in the plate circuit linking the Australia, Antarctic, and Pacific plates, the researchers also found. Too, the 180-kilometer-wide zone of extension is most likely related to the uplift that has occurred in the Transantarctic Mountains to the west, and explains other geological features that have hitherto been puzzling.

And finally, the new results could shed new light on global issues such as the motion between hotspots in the Pacific and Indo-Atlantic oceans.

In addition to Cande and Stock, the other authors are Dietmar Müller of the University of Sidney and Takemi Ishihara of the Geological Survey of Japan.

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Robert Tindol
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Astrobiologists should look for both water and energy sources when searching for life on other worlds, researcher says

PASADENA—When planetary scientists first saw evidence of a water ocean beneath the frozen surface of Europa, everyone immediately began pondering the likelihood that the Jovian moon could harbor advanced life forms—perhaps even fishlike creatures.

But last summer a group of planetary scientists from the California Institute of Technology and Jet Propulsion Laboratory threw water on the theory—so to speak—when they took a novel approach and concluded that advanced life forms were not likely.

"Water is a good place to look for life, but is only one ingredient for life," says Kenneth Nealson, an astrobiologist who holds joint appointments at Caltech and JPL, and who was a coauthor of the 1999 paper on Europa.

"You also need energy and, probably, organic carbon."

Nealson and his colleagues Eric Gaidos and Joseph Kirschvink (both of Caltech) wrote in the controversial 1999 Science paper that life on Earth is not necessarily the best analogy for life on another world. In other words, astrobiologists should be prepared to use chemistry and physics to analyze the possibilities for extraterrestrial life, rather than merely assuming life will exist wherever there is water.

Specifically, the authors showed that nearly all forms of energy used by life on Earth would be unavailable to the organisms that might live beneath Europa's surface ice layer. This did not preclude primitive unicellular organisms, but boded poorly for anyone hoping to someday see Europan creatures with gills and backbones.

"There is a trap in the thinking, because on Earth, virtually everywhere you find water you also find life," Nealson says. "And conversely, on Earth, about the only thing you can associate with lifelessness is the lack of water.

"But on another planet, just because you find water doesn't mean you're necessarily going to find life there."

Nealson says that a very likely place to look for life forms is any place where there is an energy gradient of some sort. Some potential energy gradients that might be available on Europa might arise from the gravitational and magnetic fields of Jupiter, which would almost certainly grind things around inside the moon and result in a heat source.

But when Nealson and his colleagues last year analyzed the closed system beneath Europa, they concluded that this source of energy alone was probably insufficient for multicellular life to survive. Also, they concluded that the redox energy (or available chemical energy) of the moon would also be inadequate for complex life of the kind we are familiar with on Earth.

"Still, I think Europa is a great place to look for very simple organisms," Nealson says today.

Another salubrious way to look for life is to look carefully at any place there is a water cycle, however small. If any of the other Jovian moons, such as Ganymede or Callisto, have a hydrological cycle in which moisture precipitates and runs underground, is heated by an internal source, and ultimately is returned to the surface, then the planet or moon would have the potential for energy gradients, energy flow, and geochemical cycling. All of these may be key to the existence of global life.

And the water cycle could be entirely subterranean and could even be a very limited, closed loop, Nealson says. For example, Mars may still have frozen subterranean waters that are occasionally melted by the planet's internal heat, but never result in water vapor actually surfacing. In such a case, there could be bacterial life that has lived in a closed loop beneath the Martian surface for billions of years.

"There's certainly no present-day atmospheric water cycle on Mars—no rain, no aquifers to collect the rainfall, no recycling," he says. "So if there's life on Mars, it has a hard time existing, and we'd have a hard time finding it without drilling."

While a drilling excavation to Mars is still a few decades in the future, Nealson hopes that one of the orbiters to Mars will soon include a deep-sounding radar instrument. Such an instrument can detect either liquid or frozen water beneath the surface.

The Mars orbiter scheduled for launch in 2003 by the European Space Agency (in conjunction with scientists from JPL) is scheduled to have deep-sounding radar for the detection of subsurface liquid water. A similar device will eventually be sent to Europa.

Perhaps later, the search could be extended to other Jovian moons, as well as the moons of Saturn and even Uranus.

"The moons of Jupiter have changed the way I feel about life in the solar system," Nealson says. "Each of the four large moons has different properties, different energy flows, different likelihoods of water.

"It's important to keep an open mind," he says.

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Robert Tindol
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Snowball Earth episode 2.4 billion years ago was hard on life, but good for modern industrial economy, research shows

PASADENA-For the primitive organisms unlucky enough to be around 2.4 billion years ago, the first global freeze was a real wipeout, likely the worst in the history of life on Earth. Few of the organisms escaped extinction, and those that did were forced into an evolutionary bottleneck that altered the diversity of life for eons.

But 2.4 billion years later, an unlikely winner has emerged from that first planetary deep-freeze, and it's none other than us modern industrial humans. New research from the California Institute of Technology reveals that the world's largest deposit of manganese (a component of steel) was formed by the cascade of chemical reactions caused when the planet got so cold that even the equators were icy-a condition now known as "Snowball Earth."

In a special issue of the Proceedings of the National Academy of Sciences on global climatic change published February 14, Caltech geobiology professor Joe Kirschvink and his team show that the huge Kalahari Manganese Field in southern Africa was a consequence of a long Snowball Earth episode. Kirschvink, who originated the Snowball Earth concept more than a decade ago, says the new study explains how the drastic climatic changes in a Snowball Earth episode can alter the course of biological evolution, and can also account for a huge economic resource.

According to Kirschvink and his team, the planet froze over for tens of millions of years, but eventually thawed when a greenhouse-induced effect kicked in. This warming episode led to the deposit of iron formations and carbonates, providing nutrients to the blue-green algae that were waiting in the wings for a good feeding.

The algae bloom during the melting period resulted in an oxygen spike, which in turn led to a "rusting" of the iron and manganese. This caused the manganese to be laid down in a huge 45-meter-thick deposit in the Kalahari to await future human mining and metallurgy. Today, about 80 percent of the entire world's known manganese reserves are found in that one field, and it is a major economic resource for the Republic of South Africa.

The Snowball Earth's cascade of climatic chemical reactions also probably forced the living organisms of the time to mutate in such a way that they were protected from the excess oxygen. Because free radicals can cause DNA damage, the organisms adapted an enzyme known as the superoxide dismutase to compensate.

Kirschvink points out that the enzyme and its evolutionary history are well known to biologists, but that a global climate change apparently has never been suggested as a cause of the enzyme's diversification.

"To our knowledge, this is the first biochemical evidence for this adaptation," says Kirschvink, adding that the data shows that the adaptation can be traced back to the Snowball Earth episode 2.4 billion years ago.

Kirschvink, his former doctoral student Dave Evans (now at the University of Western Australia in Perth), and Nicolas J. Beukes of Rand Afrikaans University proposed the Snowball Earth episode in a 1997 paper in Nature. Their evidence for the freeze of 2.4 billion years ago was based on their finding evidence of glacial deposits in a place in southern Africa that in ancient times was within 11 degrees of the equator, according to magnetic samples also gathered there.

The other authors of the PNAS paper are Eric Gaidos of the Jet Propulsion Laboratory, who also holds an appointment in geobiology at Caltech; L. Elizabeth Bertani and Rachel E. Steinberger, both of the Division of Biology at Caltech; and Nicholas J. Beukes and Jans Gutzmer, both of Rand Afrikaans University in Johannesburg.

The work was supported by the NASA National Astrobiology Institute.

A detailed article on the Snowball Earth phenomenon was published in the January 2000 issue of Scientific American.

Writer: 
Robert Tindol
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Thunderstorms found to be an energy source for Jupiter's Great Red Spot

PASADENA-Using data from the Galileo spacecraft currently in orbit around Jupiter, scientists have discovered that thunderstorms beneath the upper cloud cover are supplying energy to the planet's colorful large-scale weather patterns-including the 300-year-old Great Red Spot.

In two articles in the February 10 issue of the British journal Nature and an article in the current issue of the journal Icarus, Caltech planetary science professor Andrew Ingersoll and his colleagues from Cornell, NASA, and UCLA write that lightning storms on the giant planet are clearly associated with the eddies that supply energy to the large-scale weather patterns.

Their conclusion is possible because Galileo can provide daytime photos of the cloud structure when lightning is not visible, and nighttime photos of the same area a couple of hours later clearly showing the lightning.

"You don't usually see the thunderstorms or the lightning strikes because the ammonia clouds in the upper atmosphere obscure them," says Ingersoll.

"But when Galileo passes over the night side, you can see bright flashes that let you infer the depth and the intensity of the lightning bolts."

Especially fortuitous are the Jovian nights when there is a bit of moonshine from one of the large moons such as Io, says Ingersoll. When there is no moonshine, the Galileo images show small blobs of glow from the lightning flashes, but nothing else. But when the upper cloud covers are illuminated at night by moonshine, the pictures show both the glow from the lightning some 100 kilometers below as well as eddies being roiled by the turbulence of the thunderclouds.

The association of the eddies with lightning is especially noteworthy in the new papers, Ingersoll says. Planetary scientists have known for some years that Jupiter had lightning; and in fact they have known since the Voyager flyby that the zonal jets and long-lived storms are kept alive by soaking up the energy of smaller eddies. But they did not know until now that the eddies themselves were fed by thunderstorms below.

"The lightning indicates that there's water down there, because nothing else can condense at a depth of 80 or 100 kilometers," he says. "So we can use lightning as a beacon that points to the place where there are rapidly falling raindrops and rapidly rising air columns-a source of energy for the eddies.

"The eddies, in turn, get pulled apart by shear flow and give up their energy to these large-scale features. So ultimately, the Great Red Spot gets its energy and stays alive by eating these eddies."

Adding credence to the interpretation is the fact that the anticyclonic rotation (clockwise in the northern hemisphere and counterclockwise in the southern) of the eddies is consistent with the outflow from a convective thunderstorm. Their poleward drift is consistent with anticyclones being sucked into Jupiter's powerful westward jets.

Ingersoll is lead author of the Nature paper that interprets the new Galileo data. The other authors are Peter Gierasch and Don Banfield of Cornell University; and Ashwin Vasavada of UCLA. (Banfield and Vasavada are Ingersoll's former doctoral students at Caltech).

Gierasch is lead author of the other Nature paper, which announces the discovery of moist convection on Jupiter. The other authors are Ingersoll; Banfield; Vasavada; Shawn Ewald of Caltech; Paul Helfenstein and Amy Simon-Miller, both of Cornell; and Herb Breneman and David Senske, both of NASA's Jet Propulsion Laboratory (JPL).

The authors of the Icarus paper are Ingersoll; Vasavada; Senske; Breneman; William Borucki of NASA Ames Research Center; Blane Little and Clifford Anger, both of ITRES Research in Calgary, Alberta; and the Galileo SSI Team.

The Galileo spacecraft has been orbiting Jupiter and its moons for the past four years, and the mission has begun an additional one-year extension.

JPL, a division of Caltech, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.

Writer: 
Robert Tindol
Writer: 

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