Friday, August 7, 2009

CRASHING COMETS NOT LIKELY THE CAUSE OF EARTH'S MASS EXTINCTIONS

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Scientists have debated how many mass extinction events in Earth's history were triggered by a space body crashing into the planet's surface. Most agree that an asteroid collision 65 million years ago brought an end to the age of dinosaurs, but there is uncertainty about how many other extinctions might have resulted from asteroid or comet collisions with Earth.

In fact, astronomers know the inner solar system has been protected at least to some degree by Saturn and Jupiter, whose gravitational fields can eject comets into interstellar space or sometimes send them crashing into the giant planets. That point was reinforced July 20 when a huge scar appeared on Jupiter's surface, likely evidence of a comet impact.

New University of Washington research indicates it is highly unlikely that comets have caused any mass extinctions or have been responsible for more than one minor extinction event. The work also shows that many long-period comets that end up in Earth-crossing orbits likely originate from a region astronomers have long believed could not produce observable comets. A long-period comet takes from 200 years to tens of millions of years to make a single orbit of the sun.

"It was thought the long-period comets we see just tell us about the outer Oort Cloud, but they really give us a murky picture of the entire Oort Cloud," said Nathan Kaib, a University of Washington doctoral student in astronomy and lead author of a paper on the work being published July 30 in Science Express, the online edition of the journal Science.

The Oort Cloud is a remnant of the nebula from which the solar system formed 4.5 billion years ago. It begins about 93 billion miles from the sun (1,000 times Earth's distance from the sun) and stretches to about three light years away (a light year is about 5.9 trillion miles). The Oort Cloud could contain billions of comets, most so small and distant as to never be observed.

There are about 3,200 known long-period comets. Among the best-remembered is Hale-Bopp, which was easily visible to the naked eye for much of 1996 and 1997 and was one of the brightest comets of the 20th century. By comparison, Halley's comet, which reappears about every 75 years, is perhaps the best-known comet, but it is a short-period comet, most of which are believed to originate in a different part of the solar system called the Kuiper Belt.

It has been believed that nearly all long-period comets that move inside Jupiter to Earth-crossing trajectories originated in the outer Oort Cloud. Their orbits can change when they are nudged by the gravity of a neighboring star as it passes close to the solar system, and it was thought such encounters only affect very distant outer Oort Cloud bodies.

It also was believed that inner Oort Cloud bodies could reach Earth-crossing orbits only during the rare close passage of a star, which would cause a comet shower. But it turns out that even without a star encounter, long-period comets from the inner Oort Cloud can slip past the protective barrier posed by the presence of Jupiter and Saturn and travel a path that crosses Earth's orbit.

In the new research, Kaib and co-author Thomas Quinn, a UW astronomy professor and Kaib's doctoral adviser, used computer models to simulate the evolution of comet clouds in the solar system for 1.2 billion years. They found that even outside the periods of comet showers, the inner Oort Cloud was a major source of long-period comets that eventually cross Earth's path.

By assuming the inner Oort Cloud as the only source of long-period comets, they were able to estimate the highest possible number of comets in the inner Oort Cloud. The actual number is not known. But by using the maximum number possible, they determined that no more than two or three comets could have struck Earth during what is believed to be the most powerful comet shower of the last 500 million years.

"For the past 25 years, the inner Oort Cloud has been considered a mysterious, unobserved region of the solar system capable of providing bursts of bodies that occasionally wipe out life on Earth," Quinn said. "We have shown that comets already discovered can actually be used to estimate an upper limit on the number of bodies in this reservoir."

With three major impacts taking place nearly simultaneously, it had been proposed that the minor extinction event about 40 million years ago resulted from a comet shower. Kaib and Quinn's research implies that if that relatively minor extinction event was caused by a comet shower, then that was probably the most-intense comet shower since the fossil record began.

"That tells you that the most powerful comet showers caused minor extinctions and other showers should have been less severe, so comet showers are probably not likely causes of mass extinction events," Kaib said.

He noted that the work assumes the area surrounding the solar system has remained relatively unchanged for the last 500 million years, but it is unclear whether that is really the case. It is clear, though, that Earth has benefitted from having Jupiter and Saturn standing guard like giant catchers mitts, deflecting or absorbing comets that might otherwise strike Earth.

"We show that Jupiter and Saturn are not perfect and some of the comets from the inner Oort Cloud are able to leak through. But most don't," Kaib said.

(Photo: Mike Solontoi/UW)

University of Washington

SCIENTISTS DISCOVER AMAZON RIVER IS 11 MILLION YEARS OLD

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Researchers at the University of Liverpool have discovered that the Amazon river, and its transcontinental drainage, is around 11 million years old and took its present shape about 2.4 million years ago.

University of Liverpool researchers, in collaboration with the University of Amsterdam and Petrobras, the national oil company of Brazil, analysed sedimentary material taken from two boreholes near the mouth of the river to calculate the age of the Amazon river and the Amazon deep sea fan.

Prior to this study the exact age of the Amazon, one of the two largest rivers in the world, was not known. Until recently the Amazon Fan, a submarine sediment column around 10km thick, had proven difficult to penetrate. New exploration efforts by Petrobas, however, have lead to two new boreholes being drilled near the mouth of the Amazon - one 2.5miles (4.5km) below sea level - which resulted in new sedimentological and paleontological analysis of samples from the river sediment.

"River sediment records provide a unique insight into the palaeoclimate and geography of the hinterland," said Jorge Figueiredo from the University's Department of Earth and Ocean Sciences

"This new research has large implications for our understanding of South American paleogeography and the evolution of aquatic organisms in Amazonia and on the Atlantic coast. The origin of the Amazon river is a defining moment: a new ecosystem came into being at the same time as the uplifting Andes formed a geographic divide."

The study was published in the scientific journal, Geology, in July 2009.

University of Liverpool

BIZARRE WALKING BAT HAS ANCIENT HERITAGE

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A bizarre New Zealand bat that is as much at home walking four-legged on the ground as winging through the air had an Australian ancestor 20 million years ago with the same rare ability, a new study has found.

The discovery overturns a long-held held view that the agile walking and climbing skills of the lesser short-tailed bat - Mystacina tuberculata – evolved in the absence of any ground-dwelling mammal competitors or predators, says an international team of researchers led by Dr Suzanne Hand, a bat expert at the University of New South Wales, Sydney.

Along with the American common vampire bat - Desmodus rotundus - the NZ bat is one of only two of 1,100 bat species worldwide that has a true four-legged walking gait when manoeuvring on the ground.

It uses its wings as forelegs. Its thumb and toe claws have a unique extra talon for extra grip, plus a system of adhesive, gecko-like grooves in the soft, deeply wrinkled soles of its feet,

The team has found that other special muscle and bone adaptations were also present in one of its extinct rainforest-dwelling Australian ancestors, fossils of which have been found at the rich Riversleigh World Heritage Fossil Site in north-west Queensland, it says in a report published in the journal BMC Evolutionary Biology.

"The lesser short-tailed bat seems to be the sole survivor of an ancient Australian lineage now found only in New Zealand," says Dr Hand. "This study shows that, contrary to existing hypotheses, bats are not overwhelmingly absent from the ground because of competition from, or predation by, other mammals.

"Unlike for birds, there is currently no evidence that any bat has evolved a reduced capacity for flight as a result of isolation on islands.

"Rather, it would seem that walking is rare in bats because it has advantages for them only in special circumstances. Competition with other mammals and pressure from terrestrial predators does not deter modern vampire bats from walking. Likewise, the rich rainforest environment in which the ancestors of the mystacinid bats evolved in ancient Australia was teeming with ground-based competitors and predators."

A small secretive creature with velvety fur, the lesser short-tailed bat is New Zealand's only terrestrial mammal: it spends long periods on the ground in heavily forested areas, hunting insects and seeking out fruit, nectar and pollen.

It also appears to have evolved a special relationship as a pollinator for the Hades flower, or woodrose, a parasitic plant that produces nectar from blooms near ground level at the base of tree trunks.

Among other unusual traits, the bat is thought to use its teeth and claws to excavate roosting burrows and males appear to compete for mates by gathering for singing competitions in their breeding season.

University of New South Wales

A CHILDS IQ CAN BE AFFECTED BY MOTHERS EXPOSURE TO URBAN AIR POLLUTANTS

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A mother’s exposure to urban air pollutants known as polycyclic aromatic hydrocarbons (PAHs) can adversely affect a child’s intelligence quotient or IQ, a study reports. PAHs are chemicals released into the air from the burning of coal, diesel, oil and gas, or other organic substances such as tobacco. In urban areas motor vehicles are a major source of PAHs.

The study, funded by the National Institute of Environmental Health Sciences (NIEHS), a component of the National Institutes of Health, the U.S. Environmental Protection Agency and several private foundations, found that children exposed to high levels of PAHs in New York City had full scale and verbal IQ scores that were 4.31 and 4.67 points lower than those of less exposed children. High PAH levels were defined as above the median of 2.26 nanograms per cubic meter (ng/m3). A difference of four points, which was the average seen in this study, could be educationally meaningful in terms of school success, as reflected, for example, in standardized testing and other measures of academic performance. However, the researchers point out that the effects may vary among individual children.

"This research clearly shows that environmental PAHs at levels encountered in an urban setting can adversely affect a child’s IQ," said Linda Birnbaum, Ph.D., director of NIEHS. "This is the first study to report an association between PAH exposure and IQ, and it should serve as a warning bell to us all. We need to do more to prevent environmental exposures from harming our children."

The study was conducted by scientists from the Columbia University Center for Children's Environmental Health. It included children who were born to non-smoking black and Dominican-American women age 18 to 35 who resided in Washington Heights, Harlem or the South Bronx in New York. The children were followed from utero to 5 years of age. The mothers wore personal air monitors during pregnancy to measure exposure to PAHs and they responded to questionnaires.

At 5 years of age, 249 children were given an intelligence test known as the Wechsler Preschool and Primary Scale of the Intelligence, which provides verbal, performance and full-scale IQ scores. The test is regarded as a well validated, reliable and sensitive instrument for assessing intelligence. The researchers developed models to calculate the associations between prenatal PAH exposure and IQ. They accounted for other factors such as second-hand smoke exposure, lead, mother’s education and the quality of the home caretaking environment. Study participants exposed to air pollution levels below the average were designated as having low exposure, while those exposed to pollution levels above the median were identified as high exposure.

"The decrease in full-scale IQ score among the more exposed children is similar to that seen with low-level lead exposure," said lead author Frederica P. Perera, Dr.P.H., professor at Columbia’s Mailman School of Public Health and director of the Columbia Center for Children's Environmental Health.

"This finding is of concern," said Perera. "IQ is an important predictor of future academic performance, and PAHs are widespread in urban environments and throughout the world. Fortunately, airborne PAH concentrations can be reduced through currently available controls, alternative energy sources and policy interventions."

National Institutes of Health

MATHEMATICS TAKING GUESSWORK OUT OF PLASTIC SURGERY TISSUE TRANSFER

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Plastic surgeons are turning to mathematics to take the guesswork out of efforts to ensure that live tissue segments that are selected to restore damaged body parts will have enough blood and oxygen to survive the surgical transfer.

In the world’s first published mathematical model of tissue transfer, mathematicians have shown that they can use differential equations to determine which tissue segments selected for transfer from one part of the body to another location on the same body will receive the level of oxygen required to sustain the tissue.

The most common tissue transfers are used to restore body parts destroyed by cancer and trauma. The researchers say reliable mathematical modeling of the blood supply and oxygen in tissue segments will not only reduce failures in reconstructive surgery, but will also improve understanding of conditions in which an adequate blood supply is a basic problem, such as heart disease, cancer and stroke.

To obtain tissue for reconstructive surgery, plastic surgeons cut away a segment of tissue, called a flap, that is fed by a single set of perforator vessels – an artery and vein that travel through underlying muscle to support skin and fat. Surgeons generally agree that vessels at least 1.5 millimeters in diameter are required to sustain oxygen flow within the flap intended for transfer.

“That guideline is based upon experience, trial and error. What we need is a more precise ability to determine what the necessary blood vessel size really is,” said Michael Miller, professor of surgery and director of the division of plastic surgery at Ohio State University and a senior author of the research.

“I’m convinced that there is a relationship that’s probably very predictive between the diameter and blood flow in the vessel and the ability of the piece of the tissue we’re transferring to survive based on that.”

Mathematicians working on the problem have set out to model that relationship. They have shown that under certain relationships between the size of the tissue flap and the diameter of the perforator vessel, the oxygen level in the flap will remain above 15 percent of the normal level, thus ensuring a successful flap transfer. If this relationship is not satisfied, the most distant tissue from the vessel will start to die – something already observed by clinicians.

“This is still just a concept. But this initial system of five differential equations gives us a range between the flap size and the required diameter of the supporting artery that would ensure survival,” said Avner Friedman, a senior author of the paper and a Distinguished University Professor at Ohio State.

The research appears in the online early edition of the Proceedings of the National Academy of Sciences.

The routine use of a patient’s own tissue from the lower abdominal wall to restore deformities on the chest dates to 1982. In the early days of full removal and transfer of tissue, surgeons took muscle along with skin and fat, resulting in loss of strength where the muscle was removed.

“As time has gone on, we have learned that we don’t have to take the muscle, but we can take a single blood vessel coming through the muscle and transfer the tissue on that vessel,” Miller explained. “What we’re finding is that the more we design flaps like this, the less reliable the tissue is becoming. The motivation to try to reduce injury to muscle is leading to an increase in problems with part of the flap failing because it doesn’t have enough blood.”

Miller asked Friedman, founding director of Ohio State’s Mathematical Biosciences Institute, to work on a model that could add more predictability to tissue transfer.

To create the initial model, Friedman and colleagues needed to determine a number of values: the level of oxygen in the tissue, which comes from tiny capillaries spaced just microns apart; the rate of exchange of oxygen from vessels to tissue; and the pressure under which the blood is flowing in those vessels.

“The fact that there are thousands of capillaries makes it difficult to compute the oxygen levels, so we found a method of averaging. We average the oxygen concentration in the capillaries, think of capillaries as being uniformly spread all over, and look at the transport of oxygen from vessels into tissue,” Friedman said.

The model’s outcomes exploited clinical observations, in that if the oxygen pressure fell below 15 percent during the few days following the tissue transfer, fat tissue on the outer edges of the flap would start to die. When that happens on actual surgical cases, doctors must replace the dead tissue, and sometimes have to redo the entire operation.

More work lies ahead to make the model truly useful in a surgical setting, Miller and Friedman agreed.

In live human tissue, the pattern of blood vessels and capillaries is not uniformly spread throughout the flap. In many cases, there is a gap in the presence of branching vessels at the point at which the feeder artery and vein enter the fat and divide.

And to add accuracy to the parameters used in the equations, the researchers agree that animal studies of tissue transfer are needed to make the model more reliable.

Imaging technology is also expected to factor into the future of reconstructive surgery. Surgeons currently use three-dimensional CT scans to image a potential flap and the perforator vessels that are feeding that flap. But the imaging available to date can’t display the entire vasculature of a flap.

Friedman said he and colleagues hope to provide surgeons with software that could be combined with advanced imaging to supply more reliable information about the likely survival of a tissue flap.

“The surgeon will take an image of a flap that will give an idea of the distribution of vessels. Then the surgeon will use the software to determine that with this given vasculature, a specific size of tissue can be cut,” Friedman said.

Miller, a specialist in breast reconstruction, said the abdomen is a common source for tissue to be transferred because it contains a lot of tissue in a location that allows the resulting scar to be hidden by clothing.

“But theoretically, we can make flaps from anywhere on the body,” he said. “The whole body is divided up on this vascular tree. So if you can isolate a flap of tissue on a blood supply, you can remove it and reattach it.”

(Photo: OSU)

Ohio State University

FOR HORNED LIZARD, HORNS ALONE DO NOT MAKE THE SPECIES

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How do you recognize a new species? A thorough study of the million-year evolution of California's horned lizards, sometimes referred to as "horny toads," shows that when it comes to distinguishing such recently diverged species, the most powerful method integrates genetic, anatomical, and ecological information.

In the study, published in the early online edition of the journal Proceedings of the National Academy of Sciences, researchers from the University of California, Berkeley, and the U.S. Geological Survey consider all these criteria to show that when the coast horned lizard (Phrynosoma coronatum) moved north from Baja California and spread throughout the state, it diverged into at least two new species.

"When you stack up all the data sets, they all support three species," said lead author Adam Leaché, a recent UC Berkeley Ph.D. recipient who is now a National Science Foundation bioinformatics postdoctoral fellow at UC Davis. "If you were to pick only one data set, you would get a different number of species. One lesson we learned about the speciation process is that you can't rely on one type of data to accurately track a species' history."

Aside from the oldest and original species, P. coronatum, found only in southern Baja California, the researchers identified a new species, P. cerroense, in central Baja and a third, P. blainvillii, whose range extends from northern Baja to Northern California. Within the third, wide-ranging species, the study's authors found enough genetic and ecological differences to suggest there are at least three distinct populations of P. blainvillii, each requiring separate management and protection.

The findings have implications for conservation efforts, because coast horned lizard populations are in decline from southern Baja California to Northern California due to several factors. Among these are loss of lowland habitat from agriculture and urbanization and the introduction of Argentine ants, which displace the more nutritious harvester ants, the favored diet of the lizards. The lizard is on the International Union for Conservation of Nature's Red List of Threatened Species, as are California's two other horned lizards, the desert and flat-tailed horned lizards.

"For decades, it has not been clear what might be useful conservation units within the declining horned lizards in coastal California. Our study finally gives some clarity and direction for conservation actions to follow," said co-author Robert Fisher, a research biologist at the U.S. Geological Survey in San Diego, Calif.

For over 100 years, scientists have been trying to distinguish species among coast horned lizards, with the number of recognized species ranging from 1 to 6 depending on the author. These prior studies were reliant almost entirely on morphology. But when it comes to recently diverged species like the coast horned lizard, where morphological differences are subtle, it can be difficult to distinguish species, according to co-author Jimmy McGuire, UC Berkeley associate professor of integrative biology.

"This sort of analysis is going to be necessary in order to tackle questions of recent speciation," McGuire said. "Lineages that have been separated for a long time are not controversial - we have no trouble distinguishing chimps from humans, for example - but it is trickier with species that are younger and thus less morphologically heterogeneous."

"This could have an impact on the number of species that we recognize on the planet, because many species are young like this," he added.

In particular, the number of species in California could be substantially underestimated because even well-studied groups like horned lizards are likely to be comprised of multiple cryptic species, McGuire said. Studies integrating diverse data sets and focusing on the question of gene flow between lineages will almost certainly result in the discovery of many new species, he added.

Over the course of millions of years, populations of horned lizards migrating northward have separated and diverged from one another, producing an array of genetic lineages all along the western coast of North America that are adapted to unique ecological niches, according to the study.

"The genetic differences between the populations of horned lizards in California are striking - nobody could have predicted this high degree of differentiation simply by looking at the physical differences between the lizards," Leaché said.

Given enough time and continued environmental protection for the lizards to persist for the long-term, it's likely that the California horned lizards, like those in Baja California, will also evolve more dramatic physical differences through natural selection.

(Photo: Paul Bratescu)

University of California, Berkeley

STUDY FINDS HUMAN POPULATION EXPANDED DURING LATE STONE AGE

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Genetic evidence is revealing that human populations began to expand in size in Africa during the Late Stone Age approximately 40,000 years ago. A research team led by Michael F. Hammer (Arizona Research Laboratory's Division of Biotechnology at the University of Arizona) found that sub-Saharan populations increased in size well before the development of agriculture. This research supports the hypothesis that population growth played a significant role in the evolution of human cultures in the Late Pleistocene. The team's findings are published in the online peer reviewed journal PLoS ONE on July 29.

Reconstructions of the timing and magnitude of changes in human population size are important for understanding the evolution of our species. There has been a longstanding disagreement whether humans began to increase in number as a result of innovative technologies and/or behaviors formulated by hunter-gatherer groups in the Late Pleistocene, or with the advent of agriculture in the Neolithic. Hammer's research integrates empirical genetics with discoveries in paleontology and archeology to help provide answers to interdisciplinary questions about which kinds of innovations led to the evolutionary success of humankind.

Hammer's UA team, together with their collaborator from the University of California San Francisco's Institute for Human Genetics and Department of Epidemiology and Biostatistics, surveyed the genetic material of ~184 individuals from seven human populations and used a computational approach to simulate the evolution of genetic lineages over time. The researchers found that both hunter-gathers and food-producing groups best fit models with approximately ten-fold population growth beginning well before the origin of agriculture. For the first time ever, Hammer's team was able to investigate the timing of human population expansion by applying sophisticated inferential statistics to a large multilocus autosomal data set re-sequenced in multiple contemporary sub-Saharan African populations.

The team's finely executed experimental design and use of supercomputing power enabled them to determine that this expansion in population size likely began at the start of the Late Stone Age—a period in prehistory that shows an intensification of archeological sites, an increased abundance of blade-based lithic technologies, and enhanced long-distance exchange. The next step in the project is to gather more data by testing more populations and additional parts of the genome.

PLoS ONE

WARMER ENVIRONMENT MEANS SHORTER LIVES FOR COLD-BLOODED ANIMALS

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Temperature explains much of why cold-blooded organisms such as fish, amphibians, crustaceans, and lizards live longer at higher latitudes than at lower latitudes, according to research published in the Proceedings of the National Academy of Sciences (PNAS) online. Assistant Professor Dr. Stephan Munch and Ph.D. candidate Santiago Salinas, both of Stony Brook University's School of Marine and Atmospheric Sciences (SoMAS), found that for a diverse range of species whose body temperatures vary with the temperature of their surroundings, ambient temperature is the dominant factor controlling geographic variation of lifespan within species.

"We were intrigued by the fact that that pearl mussels in Spain have a maximum lifespan of 29 years, while in Russia, individuals of the same species live nearly 200 years," said Dr. Munch. "We wondered how a relatively small difference in latitude (Spain 43ºN and Russia 66ºN) could have such a drastic impact on lifespan. While one might expect that local adaptations or geographic variations in predator and food abundance would account for this disparity, we wanted to see whether the geographical variation in lifespan that we see in all sorts of species has a common physiological basis in temperature."

Munch and Salinas looked at lifespan data from laboratory and field observations for over 90 species from terrestrial, freshwater, and marine environments. They studied organisms with different average longevities--from the copepod Arcartia tonsa, which has an average lifespan of 11.6 days, to the pearl mussel Margaritifera margaritifera, which has an average lifespan of 74 years. They found that across this wide range of species, temperature was consistently exponentially related to lifespan.

The relationship between temperature and lifespan that Munch and Salinas found through data analysis was strikingly similar to the relationship that the metabolic theory of ecology (MTE) predicts. The MTE is a modeling framework that has been used to explain the way in which life history, population dynamics, geographic patterns, and other ecological processes scale with an animal's body size and temperature.

"You can think of an animal as a beaker in which chemical reactions are taking place," said Salinas. "The same rules that apply to a liquid inside a beaker should apply to animals. Chemists have a relationship for how an increase in temperature will speed up reaction rates, so the MTE borrows that relationship and applies it--with some obvious caveats--to living things."

The lifespan in 87% of the free-living species Munch and Salinas studied varied as predicted by the MTE. Yet after removing the effect of temperature, there was still considerable variation in lifespan within species, indicating that other, local factors still play a role in determining lifespan.

"It is interesting to consider how cold-blooded species are likely to react in the face of global warming," said Salinas. "Because of the exponential relationship between temperature and lifespan, small changes in temperature could result in relatively large changes in lifespan. We could see changes to ecosystem structure and stability if cold-blooded species change their life histories to accommodate warmer temperatures but warm-blooded species do not."

(Photo: Stony Brook University)

Stony Brook University

EARLIEST ANIMALS LIVED IN A LAKE ENVIRONMENT

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Conventional wisdom has it that animal evolution began in the ocean, with animal life adapting much later in Earth history to terrestrial environments.

Now a UC Riverside-led team of researchers studying ancient rock samples in South China has found that the first animal fossils in the paleontological record are preserved in ancient lake deposits, not marine sediments as commonly assumed.

"We know that life in the oceans is very different from life in lakes, and, at least in the modern world, the oceans are far more stable and consistent environments compared to lakes which tend to be short-lived features relative to, say, rates of evolution," said Martin Kennedy, a professor of geology in the Department of Earth Sciences who participated in the research. "Thus it is surprising that the first evidence of animals we find is associated with lakes, a far more variable environment than the ocean."

The study, published in the July 27-31 online edition of the Proceedings of the National Academy of Sciences, raises questions such as what aspects of the Earth's environment changed to enable animal evolution.

In their research, the authors focused on South China's Doushantuo Formation, one of the oldest fossil beds that houses highly preserved fossils dated to about 600 million years ago. These beds have no adult fossils. Instead, many of the fossils appear as bundles of cells interpreted to be animal embryos.

"Our first unusual finding in this region was the abundance of a clay mineral called smectite," said lead author Tom Bristow, who worked in Kennedy's lab. "In rocks of this age, smectite is normally transformed into other types of clay. The smectite in these South China rocks, however, underwent no such transformation and have a special chemistry that, for the smectite to form, requires specific conditions in the water – conditions commonly found in salty, alkaline lakes."

The researchers' work involved collecting hundreds of rock samples from several localities in South China, carrying out mineralogical analysis using X-ray diffraction, and collecting and analyzing other types of geochemical data.

"All our analyses show that the rocks' minerals and geochemistry are not compatible with deposition in seawater," Bristow said. "Moreover, we found smectite in only some locations in South China, and not uniformly as one would expect for marine deposits. This was an important indicator that the rocks hosting the fossils were not marine in origin. Taken together, several lines of evidence indicated to us that these early animals lived in a lake environment."

Bristow noted that the new research gives scientists a glimpse into where some of the early animals lived and what the environmental conditions were like for them – important information for addressing the broader questions of how and why animals appeared when they did.

"It is most unexpected that these first fossils do not come from marine sediments," Kennedy said. "It is possible, too, that similarly aged or older organisms also existed in marine environments and we have not found them. But at the very least our work shows that the range of early animal habitats was far more expansive than presently assumed and raises the exciting possibility that animal evolution first occurred in lakes and is tied to some environmental aspect unique to lake environments. Furthermore, because lakes are of limited size and not connected to each other, there may have been significant parallel evolution of organisms. Now we must wait and see if similar fossils are found in marine sediments."

(Photo: M. Kennedy, UC Riverside)

UC Riverside

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