Friday, July 17, 2009


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Earth's 4.5-billion-year history is filled with several turning points when temperatures changed dramatically, asteroids bombarded the planet and life forms came and disappeared. But one of the biggest moments in Earth's lifetime is the Cambrian explosion of life, roughly 540 million years ago, when complex, multi-cellular life burst out all over the planet.

While scientists can pinpoint this pivotal period as leading to life as we know it today, it is not completely understood what caused the Cambrian explosion of life. Now, researchers led by Arizona State University geologist L. Paul Knauth believe they have found the trigger for the Cambrian explosion.

It was a massive greening of the planet by non-vascular plants, or primitive ground huggers, as Knauth calls them. This period, roughly 700 million years ago virtually set the table for the later explosion of life through the development of early soil that sequestered carbon, led to the build up of oxygen and allowed higher life forms to evolve.

Knauth and co-author Martin Kennedy, of the University of California, Riverside, report their findings in the July 8 advanced on-line version of Nature ( Their paper, "The Precambrian greening of Earth," presents an alternative view of published data on thousands of analyses of carbon isotopes found in limestone that formed in the Neoproterozoic period, the time interval just prior to the Cambrian explosion.

"An explosive and previously unrecognized greening of the Earth occurred toward the end of the Precambrian and was an important trigger for the Cambrian explosion of life," said Knauth, a professor in Arizona State's School of Earth and Space Exploration.

"During this period, Earth became extensively occupied by photosynthesizing organisms," he added. "The greening was a key element in transforming the Precambrian world – which featured low oxygen levels and simple, bacteria dominant life forms – into the kind of world we have today with abundant oxygen and higher forms of plant and animal life."

Knauth calls the work "isotope geology of carbonates 101."

In order to understand what happened on Earth such a long time ago, researchers have studied the isotopic composition of limestone that formed during that period. Researchers have long studied these rocks, but Knauth said many focused only on the carbon isotopes of Neoproterozoic limestones.

Knauth and Kennedy's study looked at a bigger picture.

"There are three atoms of oxygen for every atom of carbon in limestone," Knauth says. "We looked at the oxygen isotopes as well, which allowed us to see that the peculiar carbon isotope signature previously interpreted in terms of catastrophes was always associated with intrusions of coastal ground waters during the burial transformation of initial limestone muds into rock. It's the same as we see in limestones forming today."

By gathering all of these published measurements and carefully plotting carbon isotopic data against oxygen isotopic data, a process Knauth said took three years, the researchers began to formulate a very different type of scenario for what led to complex life on Earth. Rather than a world subject to periods of life-altering catastrophes, they began to see a world that first greened up with primitive plants.

"The greening of Earth made soils which sequestered carbon and allowed oxygen to rise and get dissolved into sea water," Knauth explained. "Early animals would have loved breathing it as they expanded throughout the ocean of this new world."

A key element to this scenario is not so much what the researchers saw in the data, but what was missing. When they plotted the data for various areas from which it was derived they kept noticing an area on the plots that contained little or no data. They dubbed it the "forbidden zone."

"If previous interpretations of carbon isotope data were correct, there would be no forbidden zone on these cross plots," Knauth said. "The forbidden zone would be full of Neoproterozoic data."

"These zones show that the isotopic fingerprints in limestone we see today started in the late Precambrian and must have involved the simultaneous influx of rain water that fell on vegetated areas, infiltrated into coastal ground waters and mixed with marine pore fluids. During sea level drops, these coastal mixing zones are dragged over vast geographic regions of the flooded continents of the Neoproterozoic," Knauth said. "Vast areas of limestone can form in these mixed pore fluids."

All of which points to an environmental trigger of the Cambrian explosion of life.

"Our work presents a simple, alternative view of the thousands of carbon isotope measurements that had been taken as evidence of geochemical catastrophes in the ocean," Knauth explained. "It requires that there was an explosive greening of Earth's land surfaces with pioneer vegetation several hundred million years prior to the evolution of vascular plants, but it explains how a massive increase in Earth's oxygen could happen, which has been long postulated as necessary for animals to evolve big time."

"The isotopes are screaming that this happened in the Neoproterozoic," he added.

(Photo: L.P. Knauth, Arizona State University)

Arizona State University


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A new study carried out at the University of Haifa sheds light on how first and second languages are represented in the brain of a bilingual person. A unique single case study that was tested by Dr. Raphiq Ibrahim of the Department of Learning Disabilities and published in the Behavioral and Brain Functions journal, showed that first and second languages are represented in different places in the brain.

The question of how different languages are represented in the human brain is still unclear and, moreover, it is not certain how languages of different and similar linguistic structures are represented. Many studies have found evidence that all the languages that we acquire in the course of our life are represented in one area of the brain. However, other studies have found evidence that a second language is dissociated from the representation of a mother tongue.

According to Dr. Ibrahim, there are various ways of clarifying this question, but the best way to examine the brain's representation of two languages is by assessing the effects of brain damage on a mother tongue and on the second language of the bilingual individual. "The examination of such cases carries much significance, since it is rare that we can find people who fluently speak two languages and who have sustained brain damage that has selectively affected one of the languages. Moreover, most of the evidence in this field is derived from clinical observations of brain damage in English- and Indo-European-speaking patients, and few studies have been carried out on individuals who speak other languages, especially Semitic languages such as Hebrew and Arabic, until the present study," he added.

The present case examined a 41-year-old bilingual patient whose mother tongue is Arabic and who had fluent command of Hebrew as a second language, at a level close to that of his mother tongue. The individual is a university graduate who passed entrance exams in Hebrew and used the language frequently in his professional life. He suffered damage to the brain that was expressed in a language disorder (aphasia) that remained after completing a course of rehabilitation. During rehabilitation, a higher level of improvement in use of the Arabic language was recorded, and less for the use of Hebrew. After rehabilitation, the patient's language skills were put through various standardized tests that examined a range of levels language skills in the two languages, alongside other cognitive tests. Most of the tests revealed that damage to the patient's Hebrew skills were significantly more severe than the damage to his Arabic skills.

According to Dr. Ibrahim, even if this selective impairment of the patient's linguistic capabilities does not constitute sufficient evidence to develop a structural model to represent languages in the brain, this case does constitute an important step in this direction, particularly considering that it deals with unique languages that have not yet been studied and which are phonetically, morphologically and syntactically similar.

University of Haifa


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A rapid but superior method for computerized face recognition could revolutionize security systems especially if it can see through disguises, according to research published in the International Journal of Intelligent Systems Technologies and Applications.

Every face has special features that define that person, yet faces can also be very similar, explains Lin Huang, of Florida Atlantic University, in Boca Raton. That makes computerized face recognition for security and other applications an interesting but difficult task.

Face recognition software has been in development for many years. However, for biometric authentication at border crossings, for access to buildings, for automated banking, crime investigation, and other applications, has not yet become a mainstream application. The main technical limitation is although the systems are accurate they require a lot of computer power.

Early face recognition systems simply marked major facial features - eyes, nose mouth - on a photograph and computed the distances from these features to a common reference point. In the 1970s, a more automated approach using a facial template extended this idea to map the individual face on to a global template. By the 1980s, an almost entirely statistical approach led to the first fully automated face recognition system.

In the late 1980s researchers at Brown University developed the so-called "eigenface method", which was extended by a team at MIT in the early 1990s. Since then, approaches based on neural networks, dynamic link architectures (DLA), fisher linear discriminant model (FLD), hidden Markov models and Gabor wavelets. Then a way to create a ghost-like image that would succumb to an even more powerful analysis was developed that could accurately identify the majority of differences between faces.

However, powerful techniques have so far required powerful computers. Now, Huang and colleagues Hanqi Zhuang and Salvatore Morgera in the Department of Electrical Engineering, have applied a one-dimensional filter to the two-dimensional data from conventional analyses, such as the Gabor method. This allows them to reduce significantly the amount of computer power required without compromising accuracy.

The team tested the performance of their new algorithm on a standard database of 400 images of 40 subjects. Images are grey scale and just 92 x 112 pixels in size. They found that their technique is not only faster and works with low resolution images, such as those produced by standard CCTV cameras, but also solves the variation problems caused by different light levels and shadows, viewing direction, pose, and facial expressions. It can even see through certain types of disguises such as facial hair and glasses.

Inderscience Publishers


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An international team of researchers has studied the coralline algae fossils that lived on the last coral reefs of the Mediterranean Sea between 7.24 and 5.3 million years ago. Mediterranean algae and coral reefs began to resemble present day reefs following the isolation of the Mediterranean from the Indian Ocean and global cooling 15 and 20 million years ago respectively.

The research team from the University of Granada (UGR) and the University of Modena and Reggio Emilia (Italia) show coralline algae distribution patterns in the west and centre of the Mediterranean Sea (in Salento, Italy and Almería, Spain) by way of a fossil register of 21 species collected in the two areas.

"Coralline algae are calcareous algae that are very common nowadays, although unknown to the general public, including naturalists, and quite often in fossil form, particularly in relatively modern rocks", Juan C. Braga, the chief author and a researcher at the Stratigraphy and Paleontology Department of the UGR explained to SINC.

The study, which was published recently in Palaeogeography Palaeoclimatology Palaeoecology, describes and interprets the disappearance of the last Messinian coral reefs (between 7.24 and 5.3 million years ago) in the Mediterranean Sea. "In subsequent, more recent eras, this sea has not had the right oceanographic conditions (above all a high enough temperature) to house coral reefs," Braga added.

During the period studied by the scientists through the coralline algae fossils found in the Mediterranean, the last few reefs boasted very little coralline diversity. "This is the result of the long history of global cooling over the last 20 million years and the isolation (separation) of the Mediterranean from the Indian Ocean, some 15 million years ago," the research says.

According to the results of the research, the relative abundance of coralline algae in reefs and slope deposits is 1-5% and 18% lower respectively in the Sorbas basin (Almería) than in Salento (Italy). Furthermore, the main components of the coralline algae assemblages found in shallow water are extant species that are very common in the Mediterranean.

Other species, such as Spongites fruticulosus and Phymatolithon calcareum, have lived in the western Mediterranean for more than 25 million years. However, the typical components of present-day coral reefs, such as Hydrolithon species with thick thalli, which were no longer present in the western region of the Mediterranean 7 million years ago.

"Just like reef corallines, algae flora reflects the cooling of the Mediterranean and its isolation from the Indian Ocean, and only a few tropical biotas existed in the Messinian era. Moreover, most of them already had Atlantic affinities and resembled the algae that still inhabits our coasts today", Braga states.

The Mediterranean-Atlantic characteristics of Messinian reef corallines therefore reflect the decrease in tropical biotas that occurred during the Miocene (around 20 million years ago). According to the research team, the widespread decline of this type of algae was due to global cooling and the isolation of the Mediterranean during the middle Miocene.

(Photo: Javier Esteban)


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The efforts to identify the remains of Nicolaus Copernicus (1473-1543), found under the cathedral in Frombork, was made in a collaborative project between Swedish and Polish scientists in a team consisting of archaeologists, anthropologists and geneticists. The results is published this week in the prestigious journal PNAS (Proceedings of the National Academy of Sciences).

At Uppsala University a DNA analysis was performed of shed hairs found in a book owned by Copernicus for decades, and now kept in Museum Gustavianum at Uppsala University.

"The analysis of several hairs resulted in interpretable profiles for four of the hairs. Of these, two of the hairs have the same profile as the putative remains of Copernicus", says Marie Allen, researcher at Uppsala University.

The Uppsala researchers also made tests of a tooth as well as bone tissue from the putative remains of Copernicus. Results from the analysis of the remains from the Institute of Forensic Research in Krakow and the Museum and institute of zoology in Warsaw and the Uppsala laboratory were identical.

"Although these results points towards the materials being from the same individual, there is a probability of random match", says Marie Allen.

The DNA material in this case was limited and also degraded. Therefore, a so called mitochondrial DNA test was performed, which yields a relatively low evidentiary value. This test is commonly used in criminal investigations, but as circumstantial evidence to strengthen the case.

"The DNA results should be looked at and evaluated in the light of, and together with the information from other disciplines as the archaeological, anthropological and facial reconstruction data", says Marie Allen.

(Photo: Marie Allen)

Uppsala University


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Cartoon depictions of the first animals to emerge from the ocean and walk on land often show a simple fish with feet, venturing from water to land. But according to Jennifer Clack, a paleontologist at the University of Cambridge who has studied the fossils of these extinct creatures for more than two decades, the earliest land vertebrates — also known as tetrapods — were more diverse than we could possibly imagine.

"Some looked like crocodiles, some looked like little lizards, some like moray eels, and some were snake-like," said Clack. "They occupied all sorts of niches and habitats. And they varied tremendously in size — from about 10 cm long to 5 meters."

Long before mammals, birds, and even dinosaurs roamed the Earth, the first four-legged creatures made their first steps onto land, and quickly inhabited a wide range of terrestrial environments. These early land vertebrates varied considerably in size and shape, said Clack.

To understand the anatomical changes that accompanied this diversity, Clack teamed up with two biologists who work on living fishes — Charles Kimmel of the University of Oregon, and Brian Sidlauskas of the National Evolutionary Synthesis Center in North Carolina.

The researchers focused on 35 early tetrapods that lived between 385 and 275 million years ago. As a proxy for body size and shape, they examined the dimensions of a number of bones in a region of the skull known as the palate. By tracing changes in the length and width of interlocking bones in this part of the skull, the researchers hoped to get a more fine-grained picture of skeleton evolution as a whole.

"I tend to think the genetic instructions for making a skeleton come from how you make individual bones first, and then how you fit those bones together as a refinement of that," said developmental biologist Charles Kimmel, who was the first author on the paper.

When they mapped the changes in bone length and width onto the tetrapod family tree, the researchers discovered that not all bones changed size at the same rate or in the same direction. This phenomenon can result in an overall reshaping from one lineage to the next, explained Sidlauskas. "Sometimes a change in size can have indirect consequences for the shape of the animal," said Sidlauskas. "When different parts of an animal's body change size at different rates over evolutionary time, that can generate changes in body shape from one species to another."

Moreover, some changes are consistent with an evolutionary quirk known as paedomorphosis, in which species retain in adulthood the youthful dimensions that their ancestors had as juveniles. "Paedomorphosis is definitely there — the descendents of some groups are retaining the proportions that their juveniles had in the past," said Clack.

These results not only help explain why early tetrapods were so diverse in size and shape, but also shed light on an important chapter in the evolution of life on land – the transition from fish to amphibians.

"One of the big questions at the moment is: where did modern amphibians come from?" said Clack. "One of the hypotheses is that they have evolved by paedomorphosis and miniaturization from early tetrapods. This study lends weight to that idea."

(Photo: Jennifer Clack)

National Evolutionary Synthesis Center




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