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.

Robert Tindol

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.

Robert Tindol

Largest Explosions in the Universe May Come from the Death of Massive Stars

PASADENA-Cosmic gamma-ray bursts, the brightest known explosions in the universe, may come from the fiery deaths of very massive stars in supernova explosions, a team of astronomers said today.

In a paper to appear today in the international journal Nature, the international team led by the California Institute of Technology presents evidence that the gamma-ray burst of March 26, 1998 (GRB 980326) is apparently associated with a supernova explosion.

This would then indicate that some gamma-ray bursts are associated with the formation of black holes during the fiery deaths of very massive stars. If true, this would be some of the first direct evidence for what produces gamma-ray bursts.

As a consequence, the team suggests that a burst of gamma rays are seen when one of the jets from the supernova's central black hole is pointed directly toward Earth. Gamma-ray bursts are brilliant flashes of high-energy radiation that occur at seemingly random times and from random places in the sky.

While these objects have been known since 1967, it was only recently demonstrated that these bursts originate from galaxies in the very distant universe and are by far the most brilliant bursts in the universe. This breakthrough was made possible due to the launch of the Italian-Dutch satellite BeppoSAX in 1996, which for the first time pinpointed the location of the bursts with a sufficient accuracy to enable their detailed studies with ground-based telescopes such as the W. M. Keck Telescope.

Despite the strides, scientists were still left wondering what produces these spectacular explosions. Various theories of their possible origins are still vigorously debated.

There are currently two popular models, both suggesting that the bursts originate in a formation of a black hole. In one model, two massive objects such as neutron stars or black holes (both of which may be end-products of previous supernova explosions) coalesce, forming a single massive black hole.

In the second model, such a black hole is produced in a catastrophic collapse of the core of a massive star. In this model, one then expects two sources of light: the "afterglow'' emission from the gamma-ray burst itself and light from the exploding star, a supernova. The afterglow rapidly declines whereas the supernova explosion gains in brightness over a period of a few weeks, and then gradually fades away.

The new study reports on the observations of GRB 980326 carried out at the W. M. Keck Observatory's 10-m telescope located atop Mauna Kea, Hawaii. As in many other cases, a visible light afterglow was found following the burst, which then rapidly faded away. However, the Caltech-led team discovered something never previously observed-a dramatic rebrightening of optical emission at the position of the gamma-ray burst.

Normally, the optical light of a gamma-ray burst vastly outshines its host galaxy for weeks. When the light from the gamma-ray burst fades, the apparent total brightness remains constant: all that remains is the light from the host galaxy.

Shrinivas R. Kulkarni of the Caltech team explains, "A month after GRB 980326, it looked as though the host galaxy was dominating the light." However, the next time the team observed, some eight months after the burst, the "galaxy" was gone.

"Galaxies do not just disappear, so we were astonished," Kulkarni said. "Clearly, what we were seeing is a new source of light brightening one month and then fading away. This is something quite new."

This unexpected rebrightening is now believed to be due to the underlying supernova created in the explosion of the massive star. The team had also obtained spectra of the object at different times, and that provided additional clues.

"The spectrum of the source right after the burst was blue, which is common," said S. George Djorgovski of Caltech. "But after a month it was very red, which was unexpected.

"That alone suggested that we were looking at some different phenomenon happening at the same location, but with a time delay of a few weeks."

Both the rebrightening and the spectrum changes are naturally explained by the presence of a supernova. The intensity of the apparent re-burst matches the peak brightness of a supernova seen in a distant galaxy, and its red spectrum also has the right color.

This represents the most direct evidence to date in favor of the massive supernova model. In this scenario, a black hole is quickly formed in the center of a massive star whose core is unable to support itself against gravity.

When the star explodes, powerful jets from the central black hole emerge along the original axis of rotation, and gamma rays are created by the jets. If the jets are not pointed toward Earth, then we see only a supernova and the effects of the exploding star. But gamma rays as well as the light from the supernova arrive at Earth if the jets are pointing in our direction.

Joshua S. Bloom, a graduate student at Caltech and lead author of the paper said, "This appears to be the smoking gun for the origin of some gamma-ray bursts, a perfect marriage of the two brightest events in the universe. It is wonderful to be a part of such a discovery."

Gamma-ray bursts, since their discovery some 30 years ago, have over 150 theoretical models about their possible origins, but only a handful can come close to describing the true trigger of the bursts.

"It is possible that there are other causes for gamma-ray bursts such as the coalescence of neutron stars," Bloom said. "Undoubtedly, astronomers will focus on unearthing new classes in the years to come."

Early reports of the results created some excitement in the astronomical community. Two other groups, from universities of Amsterdam and Chicago, in view of the work presented by the Caltech team, have reanalyzed the data on some other gamma-ray bursts. They appear to find good evidence for an underlying supernova in another well-studied gamma-ray burst.

"It is encouraging to have had such a resounding reception to an unexpected result," said Kulkarni. "Even some of the initial skeptics seem to be converted by these results."

Other members of the Caltech team are graduate student A. C. Eichelberger; postdoctoral scholars P. Côté, J. P. Blakeslee, and S. C. Odewahn; and Assistant Professor F. A. Harrison.

In addition to the members of the Caltech team, the other coauthors include M. Feroci of the BeppoSAX team; D. A. Frail of the National Radio Observatory; A. V. Filippenko, D. C. Leonard, A. G. Reiss, H. Spinrad, D. Stern, A. Bunker, B. Grossan, S. Perlmutter, and R. A. Knop of the University of California at Berkeley; A. Dey of the National Optical Astronomy Observatory; and I. M. Hook of the European Southern Observatory.

Robert Tindol

Clare Boothe Luce Professorship Awarded to Caltech

PASADENA—The California Institute of Technology is pleased to announce a recent grant of $498,427, in support of a five-year Clare Boothe Luce Professorship in geobiology from the Henry Luce Foundation. Dr. Dianne Newman has been appointed to the position.

Newman's expertise in microbiology and geochemistry will allow her to explore a wide range of problems, as well as collaborate with a variety of faculty members.

"Encouraging women in science and engineering is a top priority for me personally, as well as for the Institute. The Clare Boothe Luce Professorship at Caltech helps us in a very substantial way toward that goal," says Caltech president David Baltimore.

Newman received her bachelor's degree in German studies from Stanford University in 1993, and her Ph.D. in environmental engineering from the Massachusetts Institute of Technology in 1997. In addition, she was an exchange scholar at Princeton University from 1995 to 1997, and is currently a postdoctoral fellow at Harvard.

Newman has received a number of awards, including the W.B. Dickman Writing Prize in Engineering, the American Chemical Society Award, and the NASA Planetary Biology Internship Grant. An accomplished writer and teacher, she has been recognized nationally for her research work.

The Clare Boothe Luce Program is administered by the Henry Luce Foundation, which was established by Mrs. Luce's husband, Henry R. Luce. The program was created "to encourage women to enter, study, graduate and teach" in scientific and technological fields in which they are underrepresented. Mrs. Luce established the program "in recognition that women have already entered the fields of medicine, law, business and the arts, and in order to encourage more women to enter the field of science."

Founded in 1891, Caltech has an enrollment of some 2,000 students, and an academic staff of about 280 professorial faculty and 130 research faculty. The Institute has more than 19,000 alumni. Caltech employs a staff of more than 1,700 on campus and 5,300 at JPL.

Over the years, 27 Nobel Prizes and four Crafoord Prizes have been awarded to faculty members and alumni. Forty-four 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, 69 members of the National Academy of Sciences and 49 members of the National Academy of Engineering.

Contact: Joanna Layton (626) 395-3227


Caltech joins effort to extend capabilities of major observatories

PASADENA—The California Institute of Technology will participate in a multi-institutional effort, funded by the National Science Foundation, to advance the field of adaptive optics, which promises to revolutionize astronomy.

The National Science Foundation's governing body, the National Science Board, has approved a proposal to establish a Center for Adaptive Optics at the University of California, Santa Cruz. As a partner institution, Caltech will bring together faculty from astronomy, planetary science, and physics to advance the use of existing adaptive optics technology at the 200-inch Hale Telescope at Palomar Observatory in California and the two 10-meter Keck Telescopes in Hawaii.

According to Mike Brown, assistant professor of planetary astronomy and leader of the Caltech team, "This effort will breathe new life into ground-based observing by giving us more sophisticated tools to view distant planetary systems." Depending on the size of the telescope, adaptive optics technology will make images 10 to 20 times sharper, giving scientists a much better view of space. "We plan on making Palomar the best at seeing very faint things next to very bright things, possible indicators of planetary systems. We can learn and experiment at Palomar, then utilize Keck for the really big discoveries."

Very few astronomers have any experience using adaptive optics. "We're hoping to quickly learn how to optimize the technology currently available and pass on that knowledge to other scientists. I expect this to bring about some exciting discoveries," said Brown.

Adaptive optics is a method to actively compensate for changing distortions that cause blurring of images. It is used in astronomy to correct for the blurring effect of turbulence in the earth's atmosphere. For astronomers, adaptive optics can give ground-based telescopes the same clarity of vision that space telescopes achieve by orbiting above the earth's turbulent atmosphere.

Astronomers have already started to reap the benefits of applying adaptive optics to their research. A team headed by Dr. Richard Dekany at the Jet Propulsion Laboratory recently conducted a highly successful first test of an adaptive optics system on the 200-inch Hale Telescope at Palomar Observatory. Enhanced high-resolution images of excellent quality were obtained of the ring system of Uranus and of the Lagoon Nebula.

The 27 partner institutions of the Center for Adaptive Optics will include Caltech, UC Berkeley, UC San Diego, UCLA, UC Irvine, the University of Chicago, the University of Rochester, the University of Houston, Indiana University, Lawrence Livermore National Laboratory, and 17 other national laboratory, industry, and international partners.

The center will provide the sustained effort needed to bring adaptive optics from promise to widespread use. It will conduct research, educate students, develop new instruments, and disseminate knowledge about adaptive optics to the broader scientific community.

Caltech participants will include Shri Kulkarni, Chuck Steidel, Mark Metzger, and Keith Matthews from astronomy, and Christopher Martin from physics.

Palomar Observatory is located near San Diego, Calif., and is owned and operated by Caltech. Caltech and the University of California jointly operate the W. M. Keck Observatory, which houses the world's two largest optical and infared telescopes and is located on Mauna Kea, Hawaii.

Sue Pitts McHugh

Caltech Question of the Month: If the sun ceased to exist right now, how long would mankind survive?" Would the oceans freeze?

Question: If the sun ceased to exist right now, how long would mankind survive?" Would the oceans freeze?

Submitted by Joseph Canale, La Crescenta.

Answered by Dave Stevenson, George Van Osdol Professor of Planetary Science, Caltech.

The sun provides more than just energy, it provides the gravitational force that keeps us in orbit. But I interpret the question to mean "What if the sun stopped shining?"

In that situation, Earth's surface would cool down to a state in which the outgoing infrared radiation is balanced only by conductive heat from Earth's interior. The heat content of the atmosphere is negligible except on the very short time scale of a few days.

Within days to a week, Earth's surface would cool to below the freezing point of salty water, and the oceans would begin to form a complete ice cap. In a year or so the temperature would be down below 200 degrees absolute at the surface (that's roughly minus 100 Fahrenheit). The water in the deepest part of Earth's oceans would freeze after 1,000 years. Earth's surface would not cool all the way to its new stable state of around 30 degrees absolute (approaching minus 400 Fahrenheit) until millions of years had elapsed.

This state is one in which the radioactive heat in Earth's interior balances outgoing radiation. In the interim period of several million years, Earth's subsurface would be kept warm because of the slowness of heat conduction through solid rock or ice. So the inside would stay warm even as Earth's atmosphere was freezing out as solid oxygen and nitrogen. Interestingly, this means that bacteria that live well beneath Earth's surface might survive for a while, though life right at Earth's surface would be extinguished very rapidly on a time scale of years or less. A small number of people could survive a long time by drilling and creating a habitat deep down (miles below Earth's surface).


Many life-bearing planets could exist in interstellar space, according to Caltech planetary science professor

PASADENA-Long ago in a solar system not at all far away, there could have existed about five to 10 Earth-like planets in Jupiter-crossing orbits.

These planets today could harbor life somewhere in interstellar space, according to a planetary scientist at the California Institute of Technology.

In the July 1 issue of the journal Nature, Caltech professor Dave Stevenson says in a new study that such objects could be life-sustaining due especially to the molecular hydrogen they accreted when the solar system formed long ago.

Called "interstellar planets" because they would exist between the stars but no longer in orbit around an original parent star, they have never been directly observed or proved to even exist. But based on what scientists know about the way matter should fall together in forming a solar system, such Earth-like planets could definitely have been formed.

Over a period of several million years, one of two things happened to these planets: either they slammed into Jupiter and made it even bigger, or else they came so close to Jupiter that they were catapulted by gravity completely out of the solar system, never to return.

Because these bodies formed when the solar system was permeated with hydrogen gas, they retained a dense atmosphere of hydrogen, allowing them to have surfaces with temperatures not too different from Earth, and possibly water oceans.

Stevenson writes that in the absence of sunlight, the natural radioactivity inside an Earth-like planet would only be sufficient to raise the radiating temperature of the body to 30 degrees above absolute zero (that's about minus 400 Fahrenheit). But the expected dense hydrogen atmosphere would prevent the surface from radiating effectively-just like the greenhouse effect on Earth, but more so.

As a result, the surface could have a similar temperature to the current Earth surface, allowing water oceans and a surface pressure similar to that at the bottom of Earth's oceans. For this to happen, the interstellar planet would probably need to be at least half Earth's mass.

Therefore, the energy source would be much the same as that which drives geothermal energy and plate tectonics on Earth.

It is not known whether geothermal heat alone is sufficent to allow life to originate, and the amount of energy is small compared to sunlight, suggesting that the amount of biological activity would also be small. But the existence of life in such an environment would be of great interest even if the mass of living matter were small.

The heat energy, and especially variations in temperature, could potentially allow life to get going, Stevenson says.

"I'm not saying that these objects have life, but everyone agrees that life requires disequilibrium," he says. "So there has to be a way to get free energy, because that's what drives biochemical processes.

"These objects could have weather, variations in clouds, oceans...even lightning."

If life exists on such objects, an open question is how complex it could be, Stevenson says. "I don't think anyone knows what is required to drive biological evolution from simple to very complex systems."

These interstellar wanderers could also have arisen as a natural outcome of the formation of stars, and not just during the formation of the system we live in. In either case, such planets cannot be seen with present technology because they are so dark and cold-at least from Earth's vantage point.

Although these bodies may have warm surfaces, they would appear to us as very weak emitters of long-wavelength infrared radiation, much below current detection limits.

The best bet for even demonstrating that interstellar planets exist is to have some programmed search for occultations, he says. In other words, the object might pass occasionally in the direct line of sight between Earth and a star, and if instruments were watching, the light of the star might dim or even flicker out for a time.

Programs like this are already advocated for the purpose of looking for planets in orbit around other stars. But looking for interstellar planets would be even harder.

"All I'm saying is that, among the places you might want to consider for sustainable life, you might eventually want to look at these objects. They could be the most common location for life in the universe."

Robert Tindol

Lack of Energy Makes Life on Europa Unlikely, Caltech Study Concludes

Embargoed for Release at 3 p.m. Thursday, June 3, 1999

PASADENA—Future space travelers to the watery Jovian moon Europa should probably leave their fishing tackle at home. A new study conducted by California Institute of Technology and Jet Propulsion Laboratory scientists shows that the Europan ocean is unlikely to harbor any life form more complex than single-celled organisms—and maybe not even that.

In this week's issue of the journal Science, Caltech geobiologist Eric Gaidos and coauthors Kenneth Nealson and Joseph Kirschvink show that nearly all forms of energy used by life on the Earth are unavailable to the organisms that might live beneath Europa's surface ice layer.

According to Gaidos, "One must be careful when doing comparative planetology. It is not a safe assumption to use Earth as an analogy. A liquid-water ocean on Europa does not necessarily mean there is life there."

On Earth, chemical energy is derived either from sunlight by means of photosynthesis or from the oxygen that is a byproduct. This oxygen reaches even the exotic animals inhabiting the super-hot volcanic vents in the deep sea that were discovered 20 years ago.

Even for the organisms living under ice sheets on Earth, the system is not closed. Energy from outside is available for the organisms underneath.

Unlike Earth, Europa is a closed system. The ice layer cannot be penetrated by sunlight and the only available energy in the system comes from within. This study shows that the energy available is very small compared to levels used by organisms on the Earth. It seems very unlikely that multicellular life could survive, and the lack of energy puts constraints on the likelihood of finding even hardy single-celled organisms.

Gaidos uses the analogy of an energy waterfall. "Chemical energy is falling from a high state to a low state just as water falls due to gravity. Life acts as a waterwheel in this process and harnesses the energy. However, without a source of chemical energy, the waterwheel stops."

Kirschvink adds, "Earth has a lot of metabolic energy available for life, but if you shut off the source, you shut off the system."

The study doesn't completely rule out the possibility of life, however. Gaidos says the study "assumes that the life we look for is based on the same energy sources used by life on Earth.

"The study puts limits on what life is possible," says Gaidos. "Complex life is very unlikely, but there are other possible alternatives for simple organisms to acquire the necessary energy."

One such possibility is that the organisms derive the necessary biochemical energy from oxidized iron (rust) that may exist under the ice. Other possibilities may exist, so long as there is a source of energy and life can insert its waterwheel at some point in the system.

"But we are talking about very simple organisms that can live on these energy sources. These are not multicellular creatures," Gaidos says.

Only the future will reveal what scientists might find under the ice of Europa. But we do know that no fish will be biting.

Robert Tindol

Earth's water probably didn't come from comets, Caltech researchers say

PASADENA—A new Caltech study of comet Hale-Bopp suggests that comets did not give Earth its water, buttressing other recent studies but contrary to the longstanding belief of many planetary scientists.

In the March 18 issue of Nature, cosmochemist Geoff Blake and his team show that Hale-Bopp contains sizable amounts of "heavy water," which contains a heavier isotope of hydrogen called deuterium.

Thus, if Hale-Bopp is a typical comet, and if comets indeed gave Earth its water supply billions of years ago, then the oceans should have roughly the same amount of deuterium as comets. In fact, the oceans have significantly less.

"An important question has been whether comets provided most of the water in Earth's oceans," says Blake, professor of cosmochemistry and planetary science at Caltech. "From the lunar cratering record, we know that, shortly after they were made, both the moon and Earth were bombarded by large numbers of asteroids or comets.

"Did one or the other dominate?"

The answer lies in the Blake team's measurement of a form of heavy water called HDO, which can be measured both in Earth's oceans using mass spectrometers and in comets with Caltech's Owens Valley Radio Observatory (OVRO) Millimeter Array. Just as radio waves go through clouds, millimeter waves easily penetrate the coma of a comet.

This is where cosmochemists can get a view of the makings of the comet billions of years ago, before the sun had even coalesced from an interstellar cloud. In fact, the millimeter-wave study of deuterium in water and in organic molecules in the jets emitted from the surface of the nucleus shows that Hale-Bopp is composed of 15 to 40 percent primordial material that existed before the sun formed.

The jets are quite small in extent, so the image clarity provided by the OVRO Millimeter Array was crucial in the current study. "Hale-Bopp came along at just the right time for our work," Blake says. "We didn't have all six telescopes in the array when Halley's comet passed by, and Hyakutake was a very small comet. Hale-Bopp was quite large, and so it was the first comet that could be imaged at high spatial and spectral resolution at millimeter wavelengths."

One other question that the current study indirectly addresses is the possibility that comets supplied Earth with the organic materials that contributed to the origin of life. While the study does not resolve the issue, neither does it eliminate the possibility.

Also involved in the Nature study are Charlie Qi, a graduate student in planetary science at Caltech; Michiel Hogerheijde of the UC Berkeley department of astronomy; Mark Gurwell of the Harvard-Smithsonian Center for Astrophysics, and Duane Muhleman, professor emeritus of planetary science at Caltech.

Robert Tindol

Anderson wins National Medal of Science

PASADENA-Don L. Anderson, a professor of geophysics at the California Institute of Technology, has been named a 1998 recipient of the National Medal of Science. The announcement was made at 2:45 p.m. EST today (December 8, 1998) at the White House by President Clinton.

Anderson, who holds the Eleanor and John R. McMillan Professorship at Caltech, is one of nine Americans to be awarded the country's highest scientific honor. In naming this year's recipients, Clinton cited the scientists for "their lifetime of passion, perseverance and persistence to bring about new knowledge that extends the limits of their fields and drives our nation forward into a new century."

Anderson was born in 1933 in Maryland and received his doctorate in geophysics from Caltech in 1962. He has been a leading figure in "deep Earth" research since the 1960s. He was director of the Seismological Laboratory at Caltech from 1967 to 1989.

In 1989 he published his "Theory of the Earth," a remarkable synthesis of his broad and provocative research and a guide for geo-researchers from different fields for future exploration of the dynamics of the deep parts of Earth.

Among Anderson's research interests are the changes arising from the pressure deep down in Earth's mantle. Sudden changes in the rock types at depths of 400 kilometers and 660 kilometers are explained by conversions undergone by the rock types, so that they contain minerals entirely unknown at Earth's surface. His team's research has shown that changes in composition of the mantle may explain the occurrence of tensions in Earth's crust that can lead to earthquakes.

His team has also used seismic data to study convection currents in the mantle, important for understanding continental drift and volcanism. Recently, Anderson has also used geochemical and chemical-isotope methods not only for mapping Earth's development, but also for understanding the development of the moon and the planets Mars and Venus.

The National Medal of Science was established by Congress in 1959 to be bestowed annually by the President of the United States. The first Medal of Science was awarded by John F. Kennedy in 1962 to Caltech's Theodore von Kármán, a pioneer of aerospace engineering.

To date, 362 American scientists have been awarded the Medal of Science. Of these, 44 have been Caltech professors and alumni.



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