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New Theory Provides Alternative To Big Bang
Posted: Tuesday, April 30, 2002
Source: Princeton University (http://www.princeton.edu)
A new theory of the universe suggests that space and time may not have begun in a big bang, but may have always existed in an endless cycle of expansion and rebirth.
Princeton physicist Paul Steinhardt and Neil Turok of Cambridge University described their proposed theory in an article published April 25 in an online edition of Science.
The theory proposes that, in each cycle, the universe refills with hot, dense matter and radiation, which begins a period of expansion and cooling like the one of the standard big bang picture. After 14 billion years, the expansion of the universe accelerates, as astronomers have recently observed. After trillions of years, the matter and radiation are almost completely dissipated and the expansion stalls. An energy field that pervades the universe then creates new matter and radiation, which restarts the cycle.
The new theory provides possible answers to several longstanding problems with the big bang model, which has dominated the field of cosmology for decades. It addresses, for example, the nagging question of what might have triggered or come "before" the beginning of time.
The idea also reproduces all the successful explanations provided by standard picture, but there is no direct evidence to say which is correct, said Steinhardt, a professor of physics. "I do not eliminate either of them at this stage," he said. "To me, what's interesting is that we now have a second possibility that is poles apart from the standard picture in many respects, and we may have the capability to distinguish them experimentally during the coming years."
The big bang model of the universe, originally suggested over 60 years ago, has been developed to explain a wide range of observations about the cosmos. A major element of the current model, added in the 1980s, is the theory of "inflation," a period of hyperfast expansion that occurred within the first second after the big bang. This inflationary period is critical for explaining the tremendous "smoothness" and homogeneity of the universe observed by astronomers, as well as for explaining tiny ripples in space that led to the formation galaxies.
Scientists also have been forced to augment the standard theory with a component called "dark energy" to account for the recent discovery that the expansion of the universe is accelerating.
The new model replaces inflation and dark energy with a single energy field that oscillates in such a way as to sometimes cause expansion and sometimes cause stagnation. At the same time, it continues to explain all the currently observed phenomena of the cosmos in the same detail as the big bang theory.
Because the new theory requires fewer components, and builds them in from the start, it is more "economical," said Steinhardt, who was one of the leaders in establishing the theory of inflation.
Another advantage of the new theory is that it automatically includes a prediction of the future course of the universe, because it goes through definite repeating cycles lasting perhaps trillions of years each. The big bang/inflation model has no built-in prediction about the long-term future; in the same way that inflation and dark energy arose unpredictably, another effect could emerge that would alter the current course of expansion.
The cyclic model entails many new concepts that Turok and Steinhardt developed over the last few years with Justin Khoury, a graduate student at Princeton, Burt Ovrut of the University of Pennsylvania and Nathan Seiberg of the Institute for Advanced Study.
"This work by Paul Steinhardt and Neil Turok is extraordinarily exciting and represents the first new big idea in cosmology in over two decades," said Jeremiah Ostriker, professor of astrophysics at Princeton and the Plumian Professor of Astronomy and Experimental Philosophy at Cambridge.
"They have found a simple explanation for the observed fact the universe on large scales looks the same to us left and right, up and down -- a seemingly obvious and natural condition -- that in fact has defied explanation for decades."
Sir Martin Rees, Royal Society Research Fellow at Cambridge, noted that the physics concerning key properties of the expanding universe remain "conjectural, and still not rooted in experiment or observation."
"There have been many ideas over the last 20 years," said Rees. "Steinhardt and Turok have injected an imaginative new speculation. Their work emphasizes the extent to which we may need to jettison common sense concepts, and transcend normal ideas of space and time, in order to make real progress.
"This work adds to the growing body of speculative research which intimates that physical reality could encompass far more than just the aftermath of 'our' big bang."
The cyclic universe theory represents a combination of standard physical concepts and ideas from the emerging fields of string theory and M-theory, which are ambitious efforts to develop a unified theory of all physical forces and particles. Although these theories are rooted in complex mathematics, they offer a compelling graphic picture of the cyclic universe theory.
Under these theories, the universe would exist as two infinitely large parallel sheets, like two sheets of paper separated by a microscopic distance. This distance is a extra, or fifth dimension, that is not apparent us. At our current phase in the history of the universe, the sheets are expanding in all directions, gradually spreading out and dispersing all the matter and energy they contain. After trillions of years, when they become essentially empty, they enter a "stagnant" period in which they stop stretching and, instead, begin to move toward each other as the fifth dimension undergoes a collapse.
The sheets meet and "bounce" off each other. The impact causes the sheets to be charged with the extraordinarily hot and dense matter that is commonly associated with the big bang. After the sheets move apart, they resume their expansion, spreading out the matter, which cools and coalesces into stars and galaxies as in our present universe.
The sheets, or branes, as physicists call them, are not parallel universes, but rather are facets of the same universe, with one containing all the ordinary matter we know and the other containing "we know not what," said Steinhardt. It is conceivable, he said, that a material called dark matter, which is widely believed to make up a significant part of the universe, resides on this other brane. The two sheets interact only by gravity, with massive objects in one sheet exerting a tug on matter in the other, which is what dark matter does to ordinary matter.
The movements and properties of these sheets all arise naturally from the underlying mathematics of the model, noted Steinhardt. That is in contrast to the big bang model, in which dark energy has been added simply to explain current observations.
Steinhardt and Turok continue to refine the theory and are looking for theoretical or experimental ideas that might favor one idea over the other.
"These paradigms are as far apart as you can imagine in terms of the nature of time," said Steinhardt. "On the other hand, in terms of what they predict about the universe, they are as close as you can be up to what you can measure so far.
"Yet, we also know that, with more precise observations that may be possible in the next decade or so, you can distinguish them. That is the fascinating situation we find ourselves in. It's fun to debate which ones you like better, but I really think nature will be the final arbiter here."
For further information and a graphic animation of the cyclic scenario, see http://feynman.princeton.edu/~steinh/
Editor's Note: The original news release can be found at http://www.princeton.edu/pr/pwb/02/0506/0506-cyclicuniverse.htm
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Posted: Monday, April 29, 2002
Source: NASA/Goddard Space Flight Center (http://www.gsfc.nasa.gov)
They are old but not forgotten. Nearby "retired" quasar galaxies, billions of years past their glory days as the brightest beacons in the Universe, may be the current source of rare, high-energy cosmic rays, the fastest-moving bits of matter known and whose origin has been a long-standing mystery, according to scientists at NASA and Princeton University.
The scientists have identified four elliptical galaxies that may have started this second career of cosmic-ray production, all located above the handle of the Big Dipper and visible with backyard telescopes. Each contains a central black hole of at least 100 million solar masses that, if spinning, could form a colossal battery sending atomic particles, like sparks, shooting off towards Earth at near light speed.
These findings are discussed today in a press conference at the joint meeting of the American Physical Society and the High Energy Astrophysics Division of the American Astronomical Society in Albuquerque, N.M. The team includes Dr. Diego Torres of Princeton University and Drs. Elihu Boldt, Timothy Hamilton and Michael Loewenstein of NASA's Goddard Space Flight Center in Greenbelt, Md.
Quasar galaxies are thousands of times brighter than ordinary galaxies, fueled by a central black hole swallowing copious amounts of interstellar gas. In galaxies with so-called quasar remnants, the black hole nucleus is no longer a strong source of radiation.
"Some quasar remnants might not be so lifeless after all, keeping busy in their later years," said Torres. "For the first time, we see the hint of a possible connection between the arrival directions of ultra-high energy cosmic rays and locations on the sky of nearby dormant galaxies hosting supermassive black holes."
Ultra high-energy cosmic rays represent one of astrophysics' greatest mysteries. Each cosmic ray -- essentially a single sub-atomic particle such as a proton traveling just shy of light speed -- packs as much energy as a major league baseball pitch, over 40 million trillion electron volts. (The rest energy of a proton is about a billion electron volts.) The particles' source must be within 200 million light years of Earth, for cosmic rays from beyond this distance would lose energy as they traveled through the murk of the cosmic microwave radiation pervading the Universe. There is considerable uncertainty, however, over what kinds of objects within 200 million light years could generate such energetic particles.
"The very fact that these four giant elliptical galaxies are apparently inactive makes them viable candidates for generating ultra high-energy cosmic rays," said Boldt. Drenching radiation from an active quasar would dampen cosmic-ray acceleration, sapping most of their energy, Boldt said.
The team concedes it cannot determine if the black holes in these galaxies are spinning, a basic requirement for a compact dynamo to accelerate ultra-high energy cosmic rays. Yet scientists have confirmed the existence of at least one spinning supermassive black hole, announced in October 2001. The prevailing theory is that supermassive black holes spin up as they accrete matter, absorbing orbital energy from the infalling matter.
Ultra-high-energy cosmic rays are detected by ground-based observatories, such as the Akeno Giant Air Shower Array near Yamanashi, Japan. They are extremely rare, striking the Earth's atmosphere at a rate about one per square kilometer per decade. Construction is underway for the Auger Observatory, which will cover 3,000 square kilometers (1,160 square miles) on an elevated plain in western Argentina. A proposed NASA mission called OWL (Orbiting Wide-angle Light-collectors) would detect the highest-energy cosmic rays by looking down on the atmosphere from space.
Loewenstein joins NASA Goddard's Laboratory for High Energy Astrophysics as a research associate with the University of Maryland, College Park. Hamilton, also a member of the Lab, is a National Research Council fellow.
For images of the "retired" quasar galaxies, refer to: http://universe.gsfc.nasa.gov/press/images/cosmic_ray/
Editor's Note: The original news release can be found at http://www.gsfc.nasa.gov/news-release/releases/2002/02-055.htm
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Galaxy Cluster Surveys May Help Explain "Dark Energy" Posted: Wednesday, April 24, 2002
Source: University Of Illinois At Urbana-Champaign
Galaxy Cluster Surveys May Help Explain "Dark Energy" In The Universe
ALBUQUERQUE, N.M. — The universe appears to be permeated with an invisible force – dark energy – that is pushing it apart faster and faster. By conducting redshift surveys of galaxy clusters, astronomers hope to learn more about this mysterious force, and about the structure and geometry of the universe. "Galaxy clusters consist of thousands of galaxies gravitationally bound into huge structures," said Joseph Mohr, a professor of astronomy at the University of Illinois. "Because of the expansion of the universe, the clusters appear denser at larger redshifts, when the universe was younger and denser."
Galaxy cluster surveys that probe the high-redshift universe can potentially provide a wealth of information about the amount and nature of both dark matter and dark energy, said Mohr, who will present the results of an ongoing study of galaxy clusters at a meeting of the American Physical Society, to be held in Albuquerque, N.M., April 20-23.
"Till now, galaxy clusters have only been used to study the dark matter component of the universe," Mohr said. "We would measure the total mass in a galaxy cluster, and then determine the fraction of mass that was ordinary, baryonic matter."
Those measurements have shown there is insufficient baryonic and dark matter to account for the geometry of the universe. Astronomers now believe the universe is expanding at ever-increasing speed, and is dominated by a mysterious dark energy that must be doing the pushing.
"The next step is to try to figure out some of the specifics of the dark energy, such as its equation of state," Mohr said. "By mapping the redshift distribution of galaxy clusters, we should be able to measure the equation of state of dark energy, which would provide some important clues to what it is and how it came to be."
Mohr is using data collected by NASA’s Chandra X-ray Observatory to study scaling relations – such as the relationship between mass and luminosity or size – of galaxy clusters and how they change with redshift. "These scaling relations are expected to evolve with redshift, reflecting the increasing density of the universe at earlier times," Mohr said.
In particular, Mohr – in collaboration with John Carlstrom at the University of Chicago and scientists at the University of California and Harvard Smithsonian Center for Astrophysics – is studying the effect that hot electrons within galaxy clusters have on the cosmic microwave background, the afterglow of the big bang.
Galaxy clusters are filled with dark matter, galaxies and hot gas. Electrons in the gas scatter off the protons and produce X-rays. The emission of X-rays diminishes with higher redshift, because of the larger distances involved.
"There also is a tendency for the electrons to give some of their energy to the photons of the cosmic microwave background, which causes the blackbody spectrum to shift slightly," Mohr said. "The resulting distortion – called the Sunyaev-Zeldovich effect – appears as a cold spot on the cosmic microwave background at certain frequencies. Because this is a distortion in the spectrum, however, it doesn’t dim with distance like X-rays."
By comparing the X-ray emission and the Sunyaev-Zeldovich effect, Mohr can study even faint, high-redshift galaxy clusters that are currently inaccessible by other means. Such measurements, correlating galaxy cluster redshift distribution, structure and spatial distribution, should determine the equation of state of dark energy and, therefore, help define the essence of dark energy.
"Within the context of our standard structure formation scenario, galaxy surveys provide measurements of the geometry of the universe and the nature of the dark matter and dark energy," Mohr said. "But, to properly interpret these surveys, we must first understand how the structure of galaxy clusters are changing as we look backward in time."
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Galaxy Cluster Surveys May Help Explain "Dark Energy" In The Universe Posted: Wednesday, April 24, 2002
Source: University Of Illinois At Urbana-Champaign (http://www.uiuc.edu/)
ALBUQUERQUE, N.M. - The universe appears to be permeated with an invisible force - dark energy - that is pushing it apart faster and faster. By conducting redshift surveys of galaxy clusters, astronomers hope to learn more about this mysterious force, and about the structure and geometry of the universe. "Galaxy clusters consist of thousands of galaxies gravitationally bound into huge structures," said Joseph Mohr, a professor of astronomy at the University of Illinois. "Because of the expansion of the universe, the clusters appear denser at larger redshifts, when the universe was younger and denser."
Galaxy cluster surveys that probe the high-redshift universe can potentially provide a wealth of information about the amount and nature of both dark matter and dark energy, said Mohr, who will present the results of an ongoing study of galaxy clusters at a meeting of the American Physical Society, to be held in Albuquerque, N.M., April 20-23.
"Till now, galaxy clusters have only been used to study the dark matter component of the universe," Mohr said. "We would measure the total mass in a galaxy cluster, and then determine the fraction of mass that was ordinary, baryonic matter."
Those measurements have shown there is insufficient baryonic and dark matter to account for the geometry of the universe. Astronomers now believe the universe is expanding at ever-increasing speed, and is dominated by a mysterious dark energy that must be doing the pushing.
"The next step is to try to figure out some of the specifics of the dark energy, such as its equation of state," Mohr said. "By mapping the redshift distribution of galaxy clusters, we should be able to measure the equation of state of dark energy, which would provide some important clues to what it is and how it came to be."
Mohr is using data collected by NASA’s Chandra X-ray Observatory to study scaling relations - such as the relationship between mass and luminosity or size - of galaxy clusters and how they change with redshift. "These scaling relations are expected to evolve with redshift, reflecting the increasing density of the universe at earlier times," Mohr said.
In particular, Mohr - in collaboration with John Carlstrom at the University of Chicago and scientists at the University of California and Harvard Smithsonian Center for Astrophysics - is studying the effect that hot electrons within galaxy clusters have on the cosmic microwave background, the afterglow of the big bang.
Galaxy clusters are filled with dark matter, galaxies and hot gas. Electrons in the gas scatter off the protons and produce X-rays. The emission of X-rays diminishes with higher redshift, because of the larger distances involved.
"There also is a tendency for the electrons to give some of their energy to the photons of the cosmic microwave background, which causes the blackbody spectrum to shift slightly," Mohr said. "The resulting distortion - called the Sunyaev-Zeldovich effect - appears as a cold spot on the cosmic microwave background at certain frequencies. Because this is a distortion in the spectrum, however, it doesn’t dim with distance like X-rays."
By comparing the X-ray emission and the Sunyaev-Zeldovich effect, Mohr can study even faint, high-redshift galaxy clusters that are currently inaccessible by other means. Such measurements, correlating galaxy cluster redshift distribution, structure and spatial distribution, should determine the equation of state of dark energy and, therefore, help define the essence of dark energy.
"Within the context of our standard structure formation scenario, galaxy surveys provide measurements of the geometry of the universe and the nature of the dark matter and dark energy," Mohr said. "But, to properly interpret these surveys, we must first understand how the structure of galaxy clusters are changing as we look backward in time."
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Study: Universe 13 Billion Years Old Posted: Wednesday, April 24, 2002
By Paul Recer
AP Science Writer
Wednesday, April 24, 2002; 4:21 PM
WASHINGTON –– The universe is about 13 billion years old, slightly younger than previously believed, according to a study that measured the cooling of the embers in ancient dying stars.
Experts said the finding gives "very comparable results" to an earlier study that used a different method to conclude that the universe burst into existence with the theoretical "Big Bang" between 13 and 14 billion years ago.
Harvey B. Richer, an astronomer at the University of British Columbia, said the Hubble Space Telescope gathered images of the faintest dying stars it could find in M4, a star cluster some 7,000 light years away.
Richer said the fading stars, called white dwarfs, are actually burnt out coals of stars that were once up to eight times the size of the sun. After they exhausted their fuel, the stars collapsed into Earth-sized spheres of cooling embers that eventually will turn cold and wink out of sight.
Earlier studies had established the rate of cooling for these stars, said Richer. By looking at the very faintest and oldest white dwarfs possible, astronomers can use this cooling rate to estimate the age of the universe.
Speaking at a news conference Wednesday, Richer said the dimmest of the white dwarfs are about 12.7 billion years old, plus or minus about half a billion years.
Richer said it is estimated that star formation did not begin until about a billion years after the Big Bang. He said this means his best estimate for age of the universe is "about 13 billion years."
Three years ago, astronomers using another method estimated the age at 13 to 14 billion years. That was based on precise measurements of the rate at which galaxies are moving apart, an expansion that started with the Big Bang. They then back-calculated – like running a movie backward – to arrive at the age estimate.
"Our results are in very good agreement" with Richer's estimate, said Wendy L. Freedman, an astronomer at the Carnegie Observatories in Pasadena, Calif., and a leader of the group performing the universe age calculations three years ago.
Bruce Margon, an astronomer at the Space Telescope Science Institute, said both conclusions are based on "a lot of assumptions" but the fact that two independent methods arrived within 10 percent of the same answer is important.
"To find an independent way to measure the age and then get essentially the same answer is a fantastic advance," said Margon. It may not be the final answer for the universe's age, he said, but is "very, very, very close."
To get the new age estimate, the Hubble Space Telescope collected light from M4 for eight days over a 67-day period. Only then did the very faintest of the white dwarfs become visible.
"These are the coolest white dwarf stars that we know about in the universe," said Richer. "These stars get cooler and cooler and less luminous as they age."
He added: "We think we have seen the faintest ones. If we haven't, then we'll have to rethink" the conclusions.
The faintest of the white dwarfs are less than one-billionth the apparent brightness of the dimmest stars visible to the naked eye.
M4 is a globular cluster, thought to be the first group of stars that formed in the Milky Way galaxy, the home galaxy for the sun, early in the history of the universe. There are about 150 globular clusters in the Milky Way; M4 was selected because it is closest to Earth.
The new age estimate for the universe is the latest in a long series of attempts to measure the passage of time since the Big Bang. Edwin Hubble, the famed astronomer who first proved that the universe is uniformly expanding, estimated in 1928 that the universe was two billion years old.
Later studies, using the very expansion that Hubble discovered, arrived at an estimate of about nine billion years for the universe age. This created a paradox for astronomers because some stars were known to be more ancient and it is impossible for stellar bodies to be older than the universe where they formed.
Freedman and others then determined, using proven values for the brightness and distance of certain stars, that the universe throughout its history has not expanded at a constant rate. Instead, the separation of galaxies is actually accelerating, pushed by a poorly understood force known as "dark energy." By adding in calculations for this mysterious force, the Freedman group arrived at the estimate of 13 to 14 billion years.
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On the Net:
Hubble Images: http://oposite.stsci.edu/pubinfo/pr/2002/10
NASA: http://www.nasa.gov
© 2002 The Associated Press
NOTE: In accordance with Title 17 U.S.C. section 107, this material is distributed without profit or payment to those who have expressed a prior interest in receiving this information for non-profit research and educational purposes only. For more information go to: http://www.law.cornell.edu/uscode/17/107.shtml. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner.
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Great Intergalactic Cobwebs Posted: Friday, April 19, 2002
Much has been written about the first three minutes after the birth of the Universe in the Big Bang. But what do astronomers know about the next few billion years of our Universe's childhood?
Astronomers agree that matter somehow gathered together during that epoch to form stars and galaxies -- but how? Did stars appear first, or galaxies? And what was left behind in the void after they formed: empty space or vast drifting clouds of now-invisible gas?
How our Universe started -- and how it will end -- depends on the answers.
To explore such questions, astronomers turned an orbiting NASA telescope named "FUSE" (short for Far-Ultraviolet Spectroscopic Explorer) toward a distant quasar -- a brilliant, active nucleus of a galaxy some 10 billion light-years away, near the edge of the known Universe. For 20 days in August and October, 2000, FUSE collected the quasar's light in the far ultraviolet region of the electromagnetic spectrum. (Far ultraviolet radiation is about 5 times more energetic than the sunburn-causing ultraviolet rays familiar to beach-goers.) Other researchers using the Hubble Space Telescope and the gigantic ground-based Keck telescope in Hawaii monitored the quasar at ordinary ultraviolet and visual wavelengths.
Then the analyses -- and discoveries -- began. MORE
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Scientists Push Back Primate Origins From 65 Million To 85 Million Years Ago Posted: Thursday, April 18, 2002
Source: Field Museum (http://www.fieldmuseum.org/)
CHICAGO - New research that accounts for gaps in the fossil record challenges traditional methods of interpreting fossils and constructing evolutionary trees. Applying a new statistical approach to primates demonstrates that this group-from which humans developed-originated 85 million years ago (Mya) rather than 65 Mya, as is widely accepted.
This revision has implications throughout the evolutionary tree of primates, including the time of origin of the human lineage. Key findings from the new approach to interpreting the fossil record include:
* Primates originated while dinosaurs still roamed the earth. This challenges the widely accepted theory that primates could not establish a foothold until the end of the Cretaceous (65 Mya) when an asteroid cleared the way by hitting the earth and wiping out dinosaurs.
* If times of divergence within the primate tree are revised accordingly, it is likely that the divergence of humans from chimps occurred about 8 Mya rather than 5 Mya.
* An earlier origin for primates makes it very likely that continental drift played an important part in initial geographical subdivisions within primates.
* The new approach supports previously disputed findings from several molecular evolutionary trees calibrated with fossil dates from better-known parts of the mammalian tree. Calibrations outside the primates include mammal-like reptiles, horses and cetaceans (whales, dolphins and porpoises), where the fossil record is much more complete.
* Using the fossil record to date the origin of any group for which the fossil record is sparse (including certain other mammals, such as bats) is unreliable.
"Current interpretations of primate and human evolution are flawed because paleontologists have relied too heavily on direct interpretation of the known fossil record," says Robert D. Martin, PhD, vice president of academic affairs at The Field Museum and co-author of the research to be published in Nature April 18, 2002. "Our calculations indicate that we have fossil evidence for only about 5% of all extinct primates, so it's as if paleontologists have been trying to reconstruct a 1,000-piece jigsaw puzzle using just 50 pieces."
New statistical approach fills in fossil record
The earliest unequivocal primate fossils date from 55 Mya. Most paleontologists interpret this to mean that primates originated no earlier than 65 Mya.
"This view reflects the common procedure of dating the origin of a group according to the estimated stratigraphic age of the first fossil representative, and then adding a few million years," Dr. Martin explains. "This doesn't work well for primates because so few fossils have been found, many of the fossils we do have amount to a few teeth or bone fragments, and many species are known from only one fossil specimen."
The new statistical approach, however, estimates the length of time between the oldest known fossil and the earliest common ancestor of a given group. It also estimates the likely number of extinct fossil species in that group. It is based on an assumed species lifetime of 2.5 million years, the number of fossil species known in each stratigraphic interval, and the number of species alive today (taken as 235 for primates, now thought to be a minimum).
A painstaking review of the scientific literature revealed a total of 474 recorded fossil primate species. Applying the new approach to the data divided into stratigraphic intervals indicated that there were 8,000-9,000 extinct primate species.
Broad implications
These conclusions have ramifications throughout paleontology, anthropology, primatology and other disciplines. They require a rewriting of the story of primate evolution. For example, if primates originated 85 Mya, then continental drift that broke up Gondwanaland during the Cretaceous probably contributed to primate divergence.
Also, the earlier date of origin indicates that primates probably originated in southern tropical/subtropical regions and then expanded northward, rather than originating in northern regions, as is currently thought.
A complete lack of undoubted primate fossils from tropical and subtropical regions of the southern continents during the late Cretaceous (98-65 Mya) and Paleocene (65-55 Mya) has traditionally been taken as evidence that primates did not exist there during the Cretaceous. The first, abrupt appearance of primate fossils in the northern continents about 55 Mya is often taken as evidence for a northern continental origin during the Paleocene.
Contrary to this accepted theory, the authors attribute the dearth of primate fossils during the Cretaceous and Paleocene to the fact that conditions in southern latitudes did not favor fossil preservation from those times. The earliest primates were presumably quite small, which would greatly reduce the probability of fossilization and discovery.
New dates for calibrating trees
Many scientists use inferred dates of origin provided by paleontologists as temporal anchors for their work. In particular, molecular biologists have relied heavily on these derived dates when constructing a timescale for evolutionary trees of animals.
Molecular biologists estimate the length of time along branches between related species on these trees by estimating the number of changes in DNA sequences. However, there is no known way of deriving a timescale from molecular data alone.
In order to attach a timescale to a molecular tree, the standard practice has been to calibrate it using usually only one date derived from the fossil record. If the date of origin of a group derived from the fossil record is seriously underestimated, the same must be true for any molecular tree calibrated using that date.
"We hope our research will help reconcile the discrepancies between the various dates suggested by paleontologists and molecular biologists, not just for primates but for other groups of organisms, too," Dr. Martin says.
Earliest common ancestor of all primates
Existing primates can be divided into six subgroups: lemurs, lorises, tarsiers, New World monkeys, Old World monkeys, and apes and humans. Their 85-million-year-old earliest common ancestor probably looked like a primitive, small-brained version of today's dwarf lemur, according to Dr. Martin, who has studied primate evolution from many different perspectives for the past 30 years.
That animal would probably have been a nocturnal, tree-living creature weighing about 1-2 pounds, with grasping hands and feet, also used by the infant to cling to the mother's fur. It probably had large forward-facing eyes for stereovision and a shortened snout (reflecting a reduction of the anterior dentition). It would have inhabited tropical/subtropical forests, feeding on a mixed diet composed mainly of fruit and insects. Like humans, it probably had a slow pace of breeding characterized by heavy investment in a relatively small number of offspring.
The research to be published in Nature represents an unusual combination of mathematicians' statistical expertise with biologists' knowledge of primate evolution. In addition to Dr. Martin, the authors are Dr. Simon Tavaré and Dr. Oliver Will (University of Southern California in Los Angeles), Dr. Charles Marshall (Harvard University), and Dr. Christophe Soligo (Natural History Museum in London).
Note: The original news release can be found at http://www.fmnh.org/museum_info/press/press_martin.htm
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"Last Common Link"; Two Genes Diverge From One Posted: Wednesday, April 17, 2002
Source: Washington University In St. Louis (http://www.wustl.edu/)
Researcher Traces Gene Development In "Last Common Link"; Two Genes Diverge From One
A researcher studying the last common link between invertebrate and vertebrate animals has found a key genetic change that separates the spineless from the backboned.
Jeremy Gibson-Brown, Ph.D., assistant professor of biology at Washington University in St. Louis, studies amphioxus, a small marine worm, a primitive invertebrate species that is the closest living invertebrate related to vertebrates like ourselves. Gibson-Brown has found that a gene involved in the development of a body layer in invertebrates duplicated within the vertebrate lineage after the development of amphioxus.
However, in vertebrates, this gene, AmphiEomes/Tbr1, gave rise to two genes, Eomesodermin and T-brain-1, involved in brain development. While the vertebrate Eomesodermin gene has retained its original function in forming the mesoderm, or "middle skin" layer,in all vertebrate studies from fish, to amphibians to humans, the duplicate copy has lost that function and instead has evolved a role in forebrain development.
"This shows us how ‘old’ genes can give birth to new ones, and how the origins of novel developmental functions can be traced," said Gibson-Brown, who will have his results published in a forthcoming issue of the Journal of Experimental Zoology. His next step will be to look for these genes in lampreys, primitive jawless fish similar to the ancestors of later vertebrates.
"I want to see whether this gene duplication predated the separation of jawless fish and vertebrates and whether the role in forebrain development had yet been acquired."
Fruit flies, mice, worms and apes share an amazing amount of genetic information with us humans and with each other. For instance, there is only one-tenth of one percent genetic variation between a human and a chimpanzee.
A field of research has arisen to address what kinds of genetic change over time have occurred in different species to account for so many physical differences despite such genetic similarity. It is called evolutionary development.
"Evo-devo," as Gibson-Brown affectionately refers to this budding discipline, combines the principles of traditional evolutionary and developmental biology in examining the change in gene sequence and regulation that over time lead to the development of new species and eventually new body plans.
"We seek to unravel the history of the evolution of developmental programs in animals," Gibson-Brown explained. Gibson-Brown is studying the evolution of T-box genes, a group of genes that encode transcription factors regulating gene expression in embryogenesis, or the development of embryos.
Simply put, T-box genes control when and where a particular gene is turned on (expressed) or turned off during the course of an animal’s development. The vast diversity of body plans seen in animals alive today — and those who have lived in the past — are due in part to different expression patterns of these genes. T-box genes are present both in vertebrates and invertebrates, and so offer valuable insight into the emergence of new developmental programs, and hence new body plans, during the course of evolution.
Amphioxus is a small marine worm, a primitive invertebrate species whose last common ancestor with humans lived 600 million years ago. Amphioxus is the closest living invertebrate relative to the vertebrates, making it a very attractive target for Gibson-Brown’s research. He is interested in how these T-box genes, present in Amphioxus, humans and everything in between, have adapted their function and expression patterns to yield such a vast array of body plans, from worms to mice to humans.
"What I’ve been looking at is where and when these T-box genes are expressed in the development of amphioxus in order to understand the function of those genes in the last common ancestor of amphioxus and humans," Gibson-Brown said.
He has just begun work with lampreys, a very primitive vertebrate and one of the last species of jawless fish still alive today. Because lamprey ancestors evolved relatively shortly after the divergence of vertebrates from invertebrates they provide the next stepping stone in the story of T-box gene evolution.
By comparing the expression of T-box genes in Amphioxus, lamprey and mice, Gibson-Brown hopes to better understand the role that changes in gene regulation have played in the evolution of T-box genes.
"I want to understanding the regulatory elements controlling the expression of T-box genes in different species because the evolution of new developmental functions by genes is primarily achieved by the evolution of regulatory elements," he said.
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Supermassive Black Holes Powered The Most Ancient Quasars. Posted: Thursday, April 4, 2002
Source: University Of Arizona (http://www.arizona.edu)
A new survey at X-ray wavelengths of 17 distant quasars – including the three most distant quasars yet found – supports theory that predicts that supermassive black holes powered the most ancient quasars seen.
Quasars, objects larger than stars and found only in the centers of galaxies, are the brightest celestial objects in the universe. They are powered by massive black holes – objects so dense that even light cannot escape their gravity. As stars and interstellar gas fall into the black holes, they swirl around them and then are swallowed up – but not before giving off bright light at nearly all wavelengths of the electromagnetic spectrum.
University of Arizona astronomer Jill Bechtold and her colleagues used NASA's Chandra X-ray Observatory in studying a large sample of quasars no closer than 12 billion light years from Earth.
Their large survey includes three newly discovered quasars 13 billion light years from Earth -- the earliest, most distant quasars yet found. They existed when the universe was only about one billion years old, or about 7 percent of its present age.
"The objects which are shining as quasars today have lower mass black holes than the objects we see shining as these very luminous quasars in the distant past," Bechtold said. "The ancient quasars are very bright and also very rare. Basically, their black holes must exist today, but they just aren't 'quasing.' We don't know why. Probably their 'fuel' – the stars and gas falling into the black hole – has become scarce."
The three youngest quasars were discovered at optical wavelengths by the Sloan Digital Sky Survey last year. Bechtold and others have been studying X-ray observations of the three quasars made Jan. 29, 2002, with Chandra.
Bechtold and her group proposed their survey of ancient quasars in early 1998. They observed 14 very distant quasars in the early universe, between 12 billion and 12.5 billion light years away, after the launch of Chandra in mid 1999.
Bechtold's results will be published in the Astrophysical Journal.
Astronomers have suspected that the most distant quasars have more massive black holes than do nearer ones, Bechtold said. Theory predicts that coronal hot gas swirling in the accretion disk around a central supermassive black hole will emit less X-ray energy than will coronal hot gas in the disk around a smaller, closer black hole, she said.
"Our X-ray data are consistent with that," she said.
The results contradict theory that says black holes and galaxies become more massive through gravitational mergers as the universe evolves, Bechtold said.
"We see that there is strong evolution in the population of quasars. Relatively few are shining as brilliantly as the quasars we observed with Chandra, the quasars of more than 10 billion years ago.
"We want to understand what drives this evolution, and the X-rays can help tell us about what is happening close to the 'central engine' or black hole in the centers of quasars," Bechtold said.
Other astronomers reporting papers based on Chandra observations of the three youngest quasars include Niel Brandt of Pennsylvania State University, Smita Mathur of Ohio State University and Daniel Schwartz of the Harvard-Smithsonian Center for Astrophysics.
They do not reach the same conclusions, but do agree that black holes producing the X-rays are huge, given their relative youth. By various estimates, the three quasars each are somewhere between one billion and 10 billion times as massive as our sun, Bechtold said. By comparison, the black hole at the center of the Milky Way is believed to be only about 3 million times as massive as the sun.
Editor's Note: The original news release can be found here.
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Different Parts Of The Brain Handle Fantasy And Reality Posted: Tuesday, April 2, 2002
Source: Vanderbilt University (http://www.vanderbilt.edu/)
The ability to recognize objects in the real world is handled by different parts of the brain than those that allow us to imagine what the world is like. That is the result of a brain mapping experiment published in the March 28 issue of the journal Neuron. The study focused on two cognitive tasks widely used by experimental psychologists. One is mental rotation – mentally rotating a complex object into a different position to compare it with a second similar shape – and object recognition – determining whether two complex objects are the same or different.
"Mental rotation and object recognition are indistinguishable from a behavioral viewpoint: You can’t tell them apart," says the paper’s first author, Isabel Gauthier, assistant professor of psychology at Vanderbilt. "As a result, the field has been deadlocked over the question of whether the brain uses the same mechanism or different mechanisms for the two tasks."
Michael J. Tarr, one of the paper’s co-authors and professor of cognitive and linguistic sciences at Brown University, had proposed in several papers with Steven Pinker at the Massachusetts Institute of Technology that the same mechanism must be involved in the two tasks. "There are parts of our brain that are involved in our ability to imagine the world," he says. "The question is, ‘Are those the same as the parts of the brain that we use to know what things are?’ And the answer appears to be, ‘No, they are not.’"
Also collaborating on the study were William G. Hayward of Chinese University of Hong Kong and an fMRI team from the Yale School of Medicine headed by John C. Gore.
To find out what parts of the brain are involved in these two mental tasks, the researchers began with six unfamiliar geometric shapes that look something like the pieces from an unfolded Rubic’s cube. They used three of these objects – two of which were mirror images – for the mental rotation tasks and three which were slightly different but similar in appearance for the object recognition tasks. Next, they assembled a group of 15 subjects and used functional Magnetic Resonance Imaging machine to measure activity levels in different parts of their brains.
During the fMRI sessions, the researchers had the subjects perform two types of tasks using the objects. They displayed the objects in pairs on a screen and, in one case, they asked the subjects whether the two are identical or mirror images – a basic mental rotation task. In the other case, they asked them whether the two objects were the same or different – a basic object recognition task. The objects were shown at different angles from each other on the horizontal, vertical and out-of-plane axes and the researchers measured the time it took the people to answer.
When they examined the brain scans, the scientists found that the areas activated during the two tasks tended to lie on two different pathways in the visual system. These two pathways, called the ventral and dorsal, are sometimes called the "what" and "where" pathways. When asked questions about the identity of an object – for example, is it the same shape as a second object? – then the ventral pathway, which includes the temporal lobe, is activated. But when a person is asked where an object is located, the dorsal pathway, which lies in the parietal lobe, becomes active.
The first place the researchers looked was the parietal lobe because previous studies had shown that it is involved in mental rotation tasks. They confirmed these observations and found that when the difference in orientation in the mental rotation tasks was large, the amount of parietal lobe activity was greater than when the difference was small.
In the object recognition tasks, however, the researchers saw a much different pattern. They did see some activity in the parietal region. Surprisingly, however, the amount of activity in the parietal lobe decreased at larger orientation differences. In addition, they found that the brain area that did show an increase in activity with larger differences in orientation was in the ventral pathway. "This is the first indication we have that the brain doesn’t rely on the same processes to accomplish these two tasks, despite the fact that they appear to be so similar," says Gauthier.
During the course of evolution, it seems as if the same solutions have arisen more than once for similar problems in the way our brains work, adds Tarr. "They look very similar behaviorally, but it turns out they use completely different neural circuits and the brain doesn’t know how to put them together."
For more news about research at Vanderbilt, visit the online research magazine Exploration at http://exploration.vanderbilt.edu.
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