Neanderthal Males Had 'Popeye'-Like Arms?

Remains of an early Neanderthal with a super strong arm suggest that Neanderthal fellows were heavily pumped up on male hormones, possessing a hormonal status unlike anything that exists in humans today, according to a recent paper.
Neanderthal males probably evolved their ultra macho ways due to lifestyle, genes, climate and diet factors, suggests the study, published in the journal Archaeology, Ethnology & Anthropology of Eurasia.

Project leader Maria Mednikova told Discovery News that Neanderthal males hunted in the "extreme," helping to beef up one arm.

"The common method for killing animals was direct contact with the victim," said Mednikova, a professor in the Institute of Archaeology at the Russian Academy of Sciences.

Instead of shooting prey, such as mammoths, with a bow and arrow from a distance, Neanderthal males would engage in face-to-face contact, jabbing long, thick spears directly into the animal's flesh.

Neanderthal females weren't delicate creatures either.

Mednikova and her colleagues believe that "compared to anatomically modern humans, (both male and female Neanderthals) had a larger muscle mass and experienced a higher loading on the upper extremity than did Homo sapiens." Also, "they differed from modern humans by a greater functional difference between the sexes in the use of the right arm."

Neanderthal males had Popeye-type right arms, while Neanderthal females had arms that were more evenly matched and not nearly as muscular.

Mednikova and her team analyzed a fossil humerus (long bone that extends from the shoulder to the elbow) for what they believe was an Neanderthal male that might have lived around 100,000 years ago in what is now Khvalynsk, Russia. The bone was put through computerized tomography, X-rays and other analysis.

The fossil displays an unusual mixture of thickened walls with narrow bone marrow region cavities. This, according to the scientists, suggests "intense mineralization" provided for the strong, sturdy bone structure, with the inner narrowness "based on a stronger shaft architecture requiring much less mineralization."

The mixture is puzzling, because "Neanderthals demonstrate a markedly androgenic constitution," meaning they seemed to have a lot of steroids, yet these same hormones can cause reduced mineralization.

As a result, the researchers say "Neanderthals were characterized not only by peculiar biomechanical adaptations, but also by a specific hormonal condition which has no close parallels among modern human hormonal conditions either normal or pathological."

This condition might have evolved as a result of inherited genes, life in an often cold, northern climate, and an almost all-meat diet.

Mednikova and her colleagues explained that edible plants in colder regions were few and far between, and the vegetation period was short. With little fruit and vegetables, the Neanderthals became "specialized hunters who hunted terrestrial herbivores," such as mammoths and forest deer. Their diet then consisted "nearly exclusively of proteins and lipids," which must have affected their hormones and bones.

Middle Awash

Photograph by Tim D. White. Digital reconstruction of Ardipithecus ramidus modeled in resin.

The Evolutionary Road
The Middle Awash area of Ethiopia is the most persistently occupied place on Earth. Members of our lineage have lived, died, and been buried there for almost six million years. Now their bones are eroding out of the ground. Step by step they record how a primitive, small-brained primate evolved to conquer a planet. Where better to learn how we became human?

In the Afar desert of Ethiopia, there are a lot of ways to die. There is disease, of course. One can also perish from wild animal attack, snakebite, falling off a cliff, or in a shoot-out between one of the Afar clans and the Issa people across the Awash River to the east.

But life is fragile all over Africa. What is special here is the occasional durability of the deceased’s remains. The Afar Basin sits smack atop a widening rip in the Earth’s crust. Over time, volcanoes, earthquakes, and the slow accumulation of sediments have conspired to bury bones and then, much later, disgorge them to the surface as fossils. The process is ongoing. In August 2008 a young boy was taken by a crocodile in Yardi Lake, in an area of the Afar known as the Middle Awash. Three months later, Tim White, a paleoanthropologist at the University of California, Berkeley, stood at the lakeshore near where the child had died. Blanketed by lake sediments, he said, the boy’s bones had a decent chance of becoming fossils someday too. “People have been dying out here for millions of years,” said White. “Occasionally we get lucky and find what’s left .”

The Middle Awash research project, which White co-directs with his Ethiopian colleagues Berhane Asfaw and Giday WoldeGabriel, announced its greatest good fortune last October: the discovery, 15 years earlier, of the skeleton of a member of our family that had died 4.4 million years ago at a place called Aramis, less than 20 miles north of today's Yardi Lake. Belonging to the species Ardipithecus ramidus, the adult female—"Ardi" for short—is more than a million years older than the famous Lucy skeleton and much more informative about one of evolution's holy grails: the nature of the common ancestor we share with chimpanzees. In the mediaphilic field of paleoanthropology, it has become almost a reflex to claim that one's new find "overturns all previous notions" of our origins. Tim White despises such hyperbole. But in Ardi's case, it seems to be true.

Sensational as it is, however, Ar. ramidus represents just one moment in our evolutionary journey from an obscure ape to the species that holds in its hands the fate of the planet. There is no single better place on Earth to see how this transformation took place than the Middle Awash. In addition to Aramis, layers there representing 14 other time periods have yielded hominids—members of our exclusive lineage (also called hominins)—from forms even older and more primitive than Ar. ramidus to early incarnations of Homo sapiens.

White had told me that many of these "windows of time" lie in such close proximity that one could literally walk from one to another in the course of a couple of days. He invited me to join the team in the field so they could prove it. Our plan was to begin in the present at Yardi Lake and walk backward through time, peeling away what makes us human, trait by trait, species by species.

Herto: The Ancient Familiar


I rode into the field with two dozen scientists and students and six armed guards. Our caravan of 11 vehicles carried enough food and equipment for six weeks. As we threaded through the highlands, sharply terraced fields of sorghum and corn gave way to misted forests. Th e road was littered with the flotsam of mere history—around a bend the burned hulk of an army armored personnel carrier from the civil war in the 1990s and, farther on, the eroded name “MUSSOLINI” carved in the lintel above a tunnel, a legacy of the Italian occupation of the country in the 1930s.

From the top of the escarpment we switchbacked down a gargantuan staircase formed as the Arabian continental plate pulled away from Africa beginning some 30 to 25 million years ago, dropping the Afar Basin ever deeper into the rain shadow of the highlands. As we descended, the vegetation grew thinner, the sun more intense. A few hundred yards above the basin floor, we pulled over. Below us the western hills in the foreground fell toward a ragged, fault-scarred plain. On the horizon to the southeast, beyond the green ribbon of the Awash River, the highlands seemed to merge with the cone of the young volcano Ayelu. Below Ayelu was a sliver of silver: Yardi Lake.

Two days later we were walking along its shore—White, Asfaw, and WoldeGabriel, along with two longtime members of the project, geologist Bill Hart of Miami University in Ohio and Ahamed Elema, the leader of the Bouri-Modaitu Afar clan. For a while we followed the lake margin, bright dragonflies flitting about our ankles. It was the perfect setting for making fossils, now as in the past. Animals come to eat, to drink, to kill and be killed. Bones get buried, rescued from decomposition. Over eons, water trickles minerals in, organics out. White—58 years old, hard and thin as a jackal—poked with his long-handled ice ax at things newly dead. A catfish skeleton left by a fish eagle beneath an acacia tree. The head of a cow, still wearing a leathery mask of dried flesh. "If you want to become a fossil," he said, "you can't do much better than this."

Our first day's walk would take us east across an uplifted finger of land called the Bouri Peninsula, toward the Afar village of Herto. We emerged from the shade of the lake fringe and crossed some low, gray sand dunes. Soon an Afar boy and girl came with their herd of goats to investigate. The Afar are pastoralists, and except for the addition of firearms, their lives today are not substantially different from the way they were 500 years ago. As we walked in the heat among the gently bleating animals, it was easy to imagine historical time rushing backward with every step.



We approached the grass-covered huts and thornbush stockades of Herto. Asfaw, the affable former director of the National Museum of Ethiopia in Addis Ababa, pointed beneath my feet. "Careful where you step," he said. All around me, pieces of a fossil hippo skull were eroding out of the yellowish, pebbly sand. Nearby rested a teardrop-shaped stone tool, roughly five inches end to end. The Afar people do not make stone tools. We had reached our first window into the past.

In November 1997 the team was surveying where we now stood, just a couple hundred yards from the village, when one of its members spotted a fragment of a hominid skull. Its location was marked with a yellow pin flag, and the team fanned out to search for more pieces. Soon yellow flags sprouted like a field of flowers, concentrated in one spot in particular. Embedded in the sand beneath was what turned out to be a remarkably complete human skull.

While other members of the team excavated these finds, WoldeGabriel, a geologist at Los Alamos National Laboratory in New Mexico, gathered samples—pieces of obsidian and pumice, some as big as tennis balls. Such rocks, spewed in molten form by volcanic eruptions, are gold to a geologist because they can often be dated. The Herto samples were analyzed by Paul Renne of the Berkeley Geochronology Center and in Bill Hart's lab at Miami University. The results gave an age of 160,000 to 154,000 years for the skull.

The date range was immensely significant. By comparing the DNA of modern people from different regions, geneticists had long argued that the ancestry of all modern people could be traced to a population that lived in Africa between 200,000 and 100,000 years ago. But there was little fossil evidence from this time period to support the genetic model. Now there was Herto. As the broad, heavy-browed male skull emerged from its matrix of sand, it proved the perfect face for the out of Africa theory. It was a very early modern Homo sapiens—indeed, Tim White argues it is the earliest member of our own species ever found. The most amazing thing about its high, rounded braincase was the sheer size—at 1,450 cubic centimeters in volume, it's larger than that of an average living human. (A second, less complete skull found at the site may be even larger.) But the fossil's long face and a smattering of traits in the back of the skull linked it as well to earlier, more primitive forms of Homo in Africa, including a 600,000-year-old skull from the Middle Awash found by another team in 1976 at a site called Bodo, across the river.

"One thing we know about the Herto people, they had a taste for meat, especially hippos," White said, brushing some sand off a hippo skull. Many of the mammal bones collected from Herto bear cut marks from stone tools. It is impossible to say, however, whether the people were hunting the animals or scavenging the kills of other predators. Beach sands with snail shells revealed they were doing the butchering on the banks of a freshwater lake, like Yardi today. But there is no evidence of fire or other sign of occupation, so where they were living is unknown.

Coolest Stars Come out of the Dark: Spitzer Spies Frigid Brown Dwarfs

Astronomers have uncovered what appear to be 14 of the coldest stars known in our universe. These failed stars, called brown dwarfs, are so cold and faint that they'd be impossible to see with current visible-light telescopes. Spitzer's infrared vision was able to pick out their feeble glow, much as a firefighter uses infrared goggles to find hot spots buried underneath a dark forest floor.
The brown dwarfs join only a handful of similar objects previously discovered. The new objects are between the temperatures of about 450 Kelvin to 600 Kelvin (350 to 620 degrees Fahrenheit). As far as stars go, this is bitter cold -- as cold, in some cases, as planets around other stars.

These cool orbs have remained elusive for years, but will soon start coming out of the dark in droves. NASA's Wide-field Infrared Survey Explorer (WISE) mission, which is up scanning the entire sky now in infrared wavelengths, is expected to find hundreds of objects of a similarly chilly disposition, if not even colder. WISE is searching a volume of space 40 times larger than that sampled in the recent Spitzer study, which concentrated on a region in the constellation Boötes. The Spitzer mission is designed to look at targeted patches of sky in detail, while WISE is combing the whole sky.

"WISE is looking everywhere, so the coolest brown dwarfs are going to pop up all around us," said Peter Eisenhardt, the WISE project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and lead author of a recent paper in the Astronomical Journal on the Spitzer discoveries. "We might even find a cool brown dwarf that is closer to us than Proxima Centauri, the closest known star."

Brown dwarfs form like stars out of collapsing balls of gas and dust, but they are puny in comparison, never collecting enough mass to ignite nuclear fusion and shine with starlight. The smallest known brown dwarfs are about 5 to 10 times the mass of our planet Jupiter -- that's as massive as some known gas-giant planets around other stars. Brown dwarfs start out with a bit of internal heat left over from their formation, but with age, they cool down. The first confirmed brown dwarf was announced in 1995.

"Brown dwarfs are like planets in some ways, but they are in isolation," said astronomer Daniel Stern, co-author of the Spitzer paper at JPL. "This makes them exciting for astronomers -- they are the perfect laboratories to study bodies with planetary masses."

Most of the new brown dwarfs found by Spitzer are thought to belong to the coolest known class of brown dwarfs, called T dwarfs, which are defined as being less than about 1,500 Kelvin (2,240 degrees Fahrenheit). One of the objects appears to be so cold that it may even be a long-sought Y dwarf -- a proposed class of even colder stars. The T and Y classes are part of a larger system categorizing all stars; for example, the hottest, most massive stars are O stars; our sun is a G star.

"Models indicate there may be an entirely new class of stars out there, the Y dwarfs, that we haven't found yet," said co-author Davy Kirkpatrick, a co-author of the study and a member of the WISE science team at the California Institute of Technology, Pasadena, Calif. "If these elusive objects do exist, WISE will find them." Kirkpatrick is a world expert in brown dwarfs -- he came up with L, T and Y classifications for the cooler stars.

Kirkpatrick says that it's possible that WISE could find an icy, Neptune-sized or bigger object in the far reaches of our solar system -- thousands of times farther from the sun than Earth. There is some speculation amongst scientists that such a cool body, if it exists, could be a brown dwarf companion to our sun. This hypothetical object has been nicknamed "Nemesis."

"We are now calling the hypothetical brown dwarf Tyche instead, after the benevolent counterpart to Nemesis," said Kirkpatrick. "Although there is only limited evidence to suggest a large body in a wide, stable orbit around the sun, WISE should be able to find it, or rule it out altogether."

The 14 objects found by Spitzer are hundreds of light-years away -- too far away and faint for ground-based telescopes to see and confirm with a method called spectroscopy. But their presence implies that there are a hundred or more within only 25 light-years of our sun. Because WISE is looking everywhere, it will find these missing orbs, which will be close enough to confirm with spectroscopy. It's possible that WISE will even find more brown dwarfs within 25-light years of the sun than the number of stars known to exist in this space.

"WISE is going to transform our view of the solar neighborhood," said Eisenhardt. We'll be studying these new neighbors in minute detail -- they may contain the nearest planetary system to our own."

Other authors of the Spitzer paper are Roger Griffith and Amy Mainzer of JPL; Ned Wright, A.M. Ghez and Quinn Konopacky of UCLA; Matthew Ashby and Mark Brodwin of the Harvard-Smithsonian Center for Astrophysics, Cambridge; Mass., Michael Brown of Monash University, Australia; R.S. Bussmann of the University of Arizona, Tucson; Arjun Dey of National Optical Astronomy Observatory, Tucson, Ariz.; Eilat Glikman of Caltech; Anthony Gonzalez and David Vollbach of the University of Florida, Gainesville; and Shelley Wright of the University of California, Berkeley.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

JPL manages the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

For more information about Spitzer, visit http://spitzer.caltech.edu/ and http://www.nasa.gov/spitzer. More information about WISE is online at http://wise.astro.ucla.edu and http://www.nasa.gov/wise.

Oil Spills Raise Arsenic Levels in the Ocean, Says New Research

Oil spills can increase levels of toxic arsenic in the ocean, creating an additional long-term threat to the marine ecosystem, according to research published July 2 in the journal Water Research.
Arsenic is a poisonous chemical element found in minerals and it is present in oil. High levels of arsenic in seawater can enable the toxin to enter the food chain. It can disrupt the photosynthesis process in marine plants and increase the chances of genetic alterations that can cause birth defects and behavioural changes in aquatic life. It can also kill animals such as birds that feed on sea creatures affected by arsenic.

In the study, a team from Imperial College London has discovered that oil spills can partially block the ocean's natural filtration system and prevent this from cleaning arsenic out of the seawater. The researchers say their study sheds light on a new toxic threat from the Gulf of Mexico oil leak.

Arsenic occurs naturally in the ocean, but sediments on the sea floor filter it out of seawater, which keeps the levels of naturally occurring arsenic low. However, arsenic is also flushed into the ocean in wastewater from oil rigs and from accidental oil spills and leakages from underground oil reservoirs.

In the study, the researchers discovered that oil spills and leakages clog up sediments on the ocean floor with oil, which prevents the sediments from bonding with arsenic and burying it safely underground with subsequent layers of sediment. The scientists say this shutdown of the natural filtration system causes arsenic levels in seawater to rise, which means that it can enter the marine ecosystem, where it becomes more concentrated and poisonous the further it moves up the food chain.

The scientists say their work demonstrates how the chemistry of sediments in the Gulf of Mexico may be affected by the current oil leak. Professor Mark Sephton, from the Department of Earth Science and Engineering at Imperial College London, says:

"We can't accurately measure how much arsenic is in the Gulf at the moment because the spill is ongoing. However, the real danger lies in arsenic's ability to accumulate, which means that each subsequent spill raises the levels of this pollutant in seawater. Our study is a timely reminder that oil spills could create a toxic ticking time bomb, which could threaten the fabric of the marine ecosystem in the future."

Wimolporn Wainipee, postgraduate and lead author of the study from the Department of Earth Science and Engineering at Imperial College London, adds:

"We carried out our study before the leak in the Gulf of Mexico occurred, but it gives us a big insight into a potential new environmental danger in the region. Thousands of gallons of oil are leaked into the world's oceans every year from big spills, offshore drilling and routine maintenance of rigs, which means many places may be at risk from rising arsenic levels, which could in the long run affect aquatic life, plants and the people who rely on the oceans for their livelihoods."

For their research, the team analysed a mineral called goethite, one of the most abundant ocean sediments in the world, which is an iron bearing oxide.

The team carried out experiments in the laboratory that mimicked conditions in the ocean, to see how the goethite binds to arsenic under natural conditions. They discovered that seawater alters the chemistry of goethite, where low pH levels in the water create a positive change on the surface of goethite sediments, making them attractive to the negatively charged arsenic.

However, the scientists discovered that when they added oil, this created a physical barrier, covering the goethite sediments, which prevented the arsenic in the oil from binding to them. The team also found that the oil changed the chemistry of the sediments, which weakened the attraction between the goethite and arsenic.

In the future, the researchers plan to analyse other minerals such as clays and carbonates that are sediments on the ocean floor. Sediment content varies from ocean to ocean and the researchers will analyse how oil affects their ability to bind to arsenic after a spill.

Planck Unveils the Universe -- Now and Then

ESA's Planck mission has delivered its first all-sky image. It not only provides new insight into the way stars and galaxies form but also tells us how the Universe itself came to life after the Big Bang.


"This is the moment that Planck was conceived for," says ESA Director of Science and Robotic Exploration, David Southwood. "We're not giving the answer. We are opening the door to an Eldorado where scientists can seek the nuggets that will lead to deeper understanding of how our Universe came to be and how it works now. The image itself and its remarkable quality is a tribute to the engineers who built and have operated Planck. Now the scientific harvest must begin."

From the closest portions of the Milky Way to the furthest reaches of space and time, the new all-sky Planck image is an extraordinary treasure chest of new data for astronomers.

The main disc of our Galaxy runs across the centre of the image. Immediately striking are the streamers of cold dust reaching above and below the Milky Way. This galactic web is where new stars are being formed, and Planck has found many locations where individual stars are edging toward birth or just beginning their cycle of development.

Less spectacular but perhaps more intriguing is the mottled backdrop at the top and bottom. This is the 'cosmic microwave background radiation' (CMBR). It is the oldest light in the Universe, the remains of the fireball out of which our Universe sprang into existence 13.7 billion years ago.

While the Milky Way shows us what the local Universe looks like now, those microwaves show us what the Universe looked like close to its time of creation, before there were stars or galaxies. Here we come to the heart of Planck's mission to decode what happened in that primordial Universe from the pattern of the mottled backdrop.

The microwave pattern is the cosmic blueprint from which today's clusters and superclusters of galaxies were built. The different colours represent minute differences in the temperature and density of matter across the sky. Somehow these small irregularities evolved into denser regions that became the galaxies of today.

The CMBR covers the entire sky but most of it is hidden in this image by the Milky Way's emission, which must be digitally removed from the final data in order to see the microwave background in its entirety.

When this work is completed, Planck will show us the most precise picture of the microwave background ever obtained. The big question will be whether the data will reveal the cosmic signature of the primordial period called inflation. This era is postulated to have taken place just after the Big Bang and resulted in the Universe expanding enormously in size over an extremely short period.

Planck continues to map the Universe. By the end of its mission in 2012, it will have completed four all-sky scans. The first full data release of the CMBR is planned for 2012. Before then, the catalogue containing individual objects in our Galaxy and whole distant galaxies will be released in January 2011.

"This image is just a glimpse of what Planck will ultimately see," says Jan Tauber, ESA's Planck Project Scientist.

'Digital Embryo' Gains Wings: Now Possible to Film Development of Fruit Fly and of Zebrafish's Eyes and Brain

Scientists at the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, who 'fathered' the Digital Embryo have now given it wings, creating the Fly Digital Embryo.
In a study published in Nature Methods, they describe how they were able to capture fruit fly development on film, and were the first to clearly record how a zebrafish's eyes and midbrain are formed. The improved technique will also help to shed light on processes and organisms, which have so far been under-studied because they could not be followed under a microscope.

"Non-transparent samples like the fruit fly embryo scatter light, so the microscope picks up a mixture of in-focus and out-of-focus signal- good and bad information, if you like," says Ernst Stelzer, whose group carried out the project at EMBL. "Our new technique enables us to discriminate between that good and bad information, so it allows us to record organisms which have so far been poorly studied, because of their unfortunate optical properties."

Philipp Keller, who co-led and conducted the work, and Ernst Stelzer overcame the difficulties caused by thick, opaque samples, by shining patterns of light on them, instead of the usual continuous light sheet. This generates an image with alternating light and dark stripes, unless the light bounces off the sample and changes direction, in which case this stripy pattern will be blurred. By taking multiple images of different phases of the light pattern, and combining them, a computer can filter out the effects of scattered light and generate an accurate image of the sample, thus enabling scientists to record images that were previously unobtainable.

By combining this approach with imaging along different angles, the scientists were able to obtain three-dimensional movies of the developing fruit fly embryo in spite of the fact that it is almost opaque.

The EMBL scientists were also able to extend their recordings of zebrafish development to an unprecedented level. They took around one million images to capture the first three days of zebrafish development from three different angles, generating films in which the formation of the animal's eyes and midbrain are clearly visible.

"Of course, getting such good images is nice for the human observer, but it's particularly crucial for computational analyses, like tracking cell movements and divisions as we do in the Digital Embryo," says Philipp Keller, now at the Janelia Farm Research Campus of the Howard Hughes Medical Institute in Ashburn, VA, USA.

The work was done in collaboration with scientists at the University of Heidelberg, Germany and the Sloan-Kettering Institute in New York, USA. All data, images and videos are freely available online, alongside the data from the digital embryo, at www.digital-embryo.org.

Constraining the Reign of Ancient Egypt: Radiocarbon Dating Helps to Nail Down the Chronology of Kings, Researchers Say

For several thousands of years, ancient Egypt dominated the Mediterranean world -- and scholars across the globe have spent more than a century trying to document the reigns of the various rulers of Egypt's Old, Middle and New Kingdoms. Now, a detailed radiocarbon analysis of short-lived plant remains from the region is providing scientists with a long and accurate chronology of ancient Egyptian dynasties that agrees with most previous estimates but also imposes some historic revisions.
Although previous chronologies have been precise in relative ways, assigning absolute dates to specific events in ancient Egyptian history has been an extremely contentious undertaking. This new study tightly constrains those previous predictions, especially for the Old Kingdom, which was determined to be slightly older than some scholars had believed. The study will also allow for more accurate historical comparisons to surrounding areas, like Libya and Sudan, which have been subject to many radiocarbon dating techniques in the past.

Christopher Bronk Ramsey and colleagues from the Universities of Oxford and Cranfield in England, along with a team of researchers from France, Austria and Israel, collected radiocarbon measurements from 211 various plants -- obtained from museum collections in the form of seeds, baskets, textiles, plant stems and fruits -- that were directly associated with particular reigns of ancient Egyptian kings. They then combined their radiocarbon data with historical information about the order and length of each king's reign to make a complete chronology of ancient Egyptian dynasties.

Their research is published in the June 18 issue of Science.

"My colleague, Joanne Rowland, went to a lot of museums, explaining what we were doing and asking for their participation," Bronk Ramsey said. "The museums were all very helpful in providing material we were interested in -- especially important since export of samples from Egypt is currently prohibited. Fortunately, we only needed samples that were about the same size as a grain of wheat."

The researchers' new chronology does indicate that a few events occurred earlier than previously predicted. It suggests, for example, that the reign of Djoser in the Old Kingdom actually started between 2691 and 2625 B.C. and that the New Kingdom began between 1570 and 1544 B.C.

Bronk Ramsey and his colleagues also found some discrepancies in the radiocarbon levels of the Nile Valley, but they suggest that these are due to ancient Egypt's unusual growing season, which is concentrated in the winter months.

For the most part, the new chronology simply narrows down the various historical scenarios that researchers have been considering for ancient Egypt.

"For the first time, radiocarbon dating has become precise enough to constrain the history of ancient Egypt to very specific dates," said Bronk Ramsey. "I think scholars and scientists will be glad to hear that our small team of researchers has independently corroborated a century of scholarship in just three years."

This report by Bronk Ramsey et al. was funded by the Leverhulme Trust with additional financial support from the German-Israeli Foundation for Scientific Research and Development, NERC, CNRS, CEA, IRSN, IRD, and Ministère de La Culture.

Oldest Apostle Images Revealed by Laser

The Apostle John

Photograph by Pier Paolo Cito, AP

A newfound painting of the Apostle John (pictured in an underground Roman tomb on Tuesday) is among the oldest known depictions of some of the original 12 Christian Apostles, experts say.

The Santa Tecla catacombs—situated beneath an office building in Rome's Ostiense area—contain fourth-century-A.D. paintings of the Apostles Paul, Peter, John, and Andrew, who were early followers of Jesus Christ.

The ancient art was revealed by lasers that burned off inches of calcium carbonate, which had accumulated on the paintings over the centuries in the humid chamber, according to Italian news reports.

The two-year restoration effort cost the Vatican—which maintains the catacombs—some $73,400 (60,000 Euros).



Catacomb Painting

Photograph by Pier Paolo Cito, AP

Paintings adorn the walls and ceiling of a Roman tomb (pictured Tuesday) where the oldest known icons of the Apostles were recently discovered.

Experts believe the Apostle depictions were painted to watch over the remains of a devout Roman noblewoman buried in the tomb, according to Italian news reports.

Early Christians—as well as other faiths—buried their dead in extensive networks of catacombs outside Rome.


Catacomb Fresco

Photograph by Pier Paolo Cito, AP

Catacomb archaeological superintendent Fabrizio Bisconti describes frescoes found in the Santa Tecla catacombs on Tuesday.

In 2009 the Vatican announced that the oldest known icon of the Apostle Paul had been found on the catacomb's ceiling.

New laser-restoration efforts have revealed that Paul's image is part of a larger work that also includes the Apostles Peter, John, and Andrew—as well as Christ himself, depicted as the Good Shepherd, according to Italian news reports.

Restorers also discovered more artwork, including the frescoes.
"I think the way they're positioned indicates a devotional dimension," Bernard P. Prusak, chair of Theology and Religious Studies at Villanova University in Pennsylvania, said in an interview.



The Good Shepherd

Photograph by Pier Paolo Cito, AP

An image of Christ as the Good Shepherd (pictured Tuesday) centers a square painting that also features iconic likenesses of four Apostles at its corners.

Villanova's Prusak noted that these four Apostles represent a rather odd grouping because they're not closely associated in the Gospels. But there's no doubt why Peter and Paul were included.

"The two important figures for Rome were Peter and Paul, who were both said to have died in Rome," he explained, "so [their images in the tomb] is a clear connection to the city."

X-Ray Satellite Homes in on a Black Hole's Jets

For decades, X-ray astronomers have studied the complex behavior of binary systems pairing a normal star with a black hole. In these systems, gas from the normal star streams toward the black hole and forms a disk around it. Friction within the disk heats the gas to millions of degrees -- hot enough to produce X-rays. At the disk's inner edge, near the black hole, strong magnetic fields eject some of the gas into dual, oppositely directed jets that blast outward at about half the speed of light.
That's the big picture, but the details have been elusive. For example, do most of the X-rays arise from the jets? The disk? Or from a high-energy region on the threshold of the black hole?

Now, astronomers using NASA's Rossi X-ray Timing Explorer (RXTE) satellite, together with optical, infrared and radio data, find that, at times, most of the X-rays come from the jets.

"Theoretical models have suggested this possibility for several years, but this is the first time we've confirmed it through multiwavelength analysis," said David Russell, lead author of the study and a post-doctoral researcher at the University of Amsterdam.

Russell and his colleagues looked at a well-studied outburst of the black-hole binary XTE J1550-564. The system lies 17,000 light-years away in the southern constellation of Norma and contains a black hole with about 10 times the sun's mass. The usually inconspicuous binary was discovered by RXTE in 1998, when the system briefly became one of the brightest X-ray sources in the sky.

Between April and July 2000, the system underwent another outburst. RXTE monitored the event in X-rays, with some additional help from NASA's Chandra X-ray Observatory. Optical and infrared observations covering the outburst came from the YALO 1-meter telescope at Cerro Tololo Inter-American Observatory in Chile, while radio observations were collected by the Australia Telescope Compact Array.

Drawing on these data, Russell and his team reconstructed a detailed picture of X-ray emission during the outburst. The study appears in the July 1 edition of Monthly Notices of the Royal Astronomical Society.

"We suspect that these outbursts are tied to increases in the amount of mass falling onto the black hole," explained Russell. "Where and how the emission occurs are the only clues we have to what's going on."

As the outburst began in mid-April 2000, the system's brightest X-ray emission was dominated by higher-energy ("hard") X-rays from a region very close to the black hole.

"We think the source of these X-rays is a region of very energetic electrons that form a corona around the innermost part of the disk," Russell said. When these electrons run into photons of visible light, the collision boosts the photons to hard X-ray energies, a process known as inverse Compton scattering. The jets were present, but only minor players.

Over the next couple of weeks, the peak X-ray emission moved to lower ("softer") energies and seems to have come from the dense gas in the accretion disk. At the same time, the hot disk quenched whatever process powers the jets and shut them down.

By late May 2000, XTE J1550-564's accretion disk was cool enough that the jets switched on again. Most of the X-rays, which were fainter but higher in energy, again came from scattering off of energetic electrons close to the black hole.

In early June, as the system faded and its peak emission gradually softened, the jets emerged as the main X-ray source. In the jet, electrons and positrons moving at a substantial fraction of light speed emit the radiation as they encounter magnetic fields, a process called synchrotron emission.

The jets require a continuous supply of particles with energies of a trillion electron volts -- billions of times the energy of visible light. "The total energy bound up in the jet is enormous, much larger than previously thought," Russell said.

As summer wore on, the jets gradually faded and their X-ray emission softened. By September, the system's brightest X-rays came from high-speed blobs of matter that the jets had hurled into space during previous eruptions.

"We're really beginning to get a handle on the 'ecology' of these extreme systems, thanks in large part to RXTE," Russell added. "We can apply what we've learned in nearby binaries like XTE J1550 to the supersized black holes and jets found at the centers of galaxies."

Launched in 1995, RXTE is still going strong. "Of currently operating NASA missions, only Hubble has been working longer," said Tod Strohmayer, the mission's project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. RXTE's unique capabilities provide insight into accreting black holes and neutron stars and allow it to detect short, faint outbursts that are easily missed by other current missions exploring the X-ray regime.

Tibetan Adaptation to High Altitude Occurred in Less Than 3,000 Years

Tibetans have mutations in numerous genes related to how the body uses oxygen. A comparison of the genomes of 50 Tibetans and 40 Han Chinese shows that ethnic Tibetans split off from the Han less than 3,000 years ago and since then rapidly evolved a unique ability to thrive at high altitudes and low oxygen levels.

The genome-wide comparison, performed by evolutionary biologists at the University of California, Berkeley, uncovered more than 30 genes with DNA mutations that have become more prevalent in Tibetans than Han Chinese, nearly half of which are related to how the body uses oxygen. One mutation in particular spread from fewer than 10 percent of the Han Chinese to nearly 90 percent of all Tibetans.

"This is the fastest genetic change ever observed in humans," said Rasmus Nielsen, UC Berkeley professor of integrative biology, who led the statistical analysis. "For such a very strong change, a lot of people would have had to die simply due to the fact that they had the wrong version of a gene."

The widespread mutation in Tibetans is near a gene called EPAS1, a so-called "super athlete gene" identified several years ago and named because some variants of the gene are associated with improved athletic performance, Nielsen said. The gene codes for a protein involved in sensing oxygen levels and perhaps balancing aerobic and anaerobic metabolism.

The new findings could steer scientists to till-now unknown genes that play a role in how the body deals with decreased oxygen, and perhaps explain some diseases, including schizophrenia and epilepsy, associated with oxygen deprivation in the womb, he said.

Nielsen and his colleagues in China and Europe report their findings in the July 2 issue of the journal Science.

Nielsen, a computational evolutionary biologist, mines genomic information to discover genetic changes driven by natural selection as humans and animals have adapted to new environments. Changes in the frequency of DNA mutations are one clue.

"You look for rapid evolution in genes because there must be something important about that gene forcing it to change so fast," he said. "The new finding is really the first time evolutionary information alone has helped us pinpoint an important function of a gene in humans."

Adaptation to low oxygen levels has allowed many peoples, from Andeans to Tibetans, to live at high altitude. When people from lower elevations move above about 13,000 feet, where oxygen levels are about 40 percent lower than at sea level, they typically tire easily, develop headaches, produce babies with lower birth weights and have a higher infant mortality rate. Tibetans have none of these problems, despite lower oxygen saturation in the blood and lower hemoglobin levels. Hemoglobin, which gives blood its red color, binds and transports oxygen to the body's tissues.

Nielsen used genome data produced by the Beijing Genomics Institute (BGI) in Shenzhen, China's flagship genome center, to tease out the genetic changes associated with these physiological changes.

"We're looking for footprints of past selection to find something functional in our genome," Nielsen said

BGI researchers obtained DNA from 50 Tibetans living in the Tibet Autonomous Region of China and 40 Han Chinese from Beijing. The Tibetans lived in two villages located at elevations of 4,300 meters (14,100 feet) and 4,600 meters (15,100 feet). All reported at least three generations of ancestors had lived at the same site. After obtaining informed consent, the Chinese researchers took blood samples from the participants and measured oxygen saturation, red blood cell concentration and hemoglobin content in their blood.

Back in the lab, the BGI team isolated only the active genes, or exons, from each individual, then used next-generation sequencing technology to sequence these so-called exomes. This involved cutting the DNA into many short pieces, sequencing each about 18 times with state-of-the-art Illumina sequencing machines, and then using overlaps to help reassemble the complete genome of each person. That work was directed by Jun Wang of BGI and the University of Copenhagen in Denmark.

Nielsen and post-doctoral fellows John E. Pool, Emilia-Huerta Sanchez and Nicolas Vinckenbosch conducted the analysis at UC Berkeley, locating all point mutations, called single-nucleotide polymorphisms (SNPs), in the 90 genomes and then comparing Tibetan and Han separately to a control group of 100 Europeans (Danes).

The analysis revealed that the common ancestors of Tibetans and Han Chinese split into two populations about 2,750 years ago, with the larger group moving to the Tibetan plateau. That group eventually shrank, while the low-elevation Han population expanded dramatically. Today, the Han Chinese are the dominant ethnic group in mainland China. The Tibetan branch either merged with the people's already occupying the Tibetan plateau, or replaced them.

"We can't distinguish intermixing and replacement," Nielsen said. "The Han Chinese and Tibetans are as different from one another as if the Han completely replaced the Tibetans about 3,000 years ago."

The Tibetan and Han Chinese genomes are essentially identical in terms of the frequency of polymorphisms in the roughly 20,000 genes, though some 30 genes stood out because of dramatic differences between the Tibetans and the Han.

"We made a list of the genes that changed the most," Nielsen said, "and what was fascinating was that, bing!, at the top of that list was a gene that had changed very strongly, and it was related to the response to oxygen."

The SNP with the most dramatic change in frequency, from 9 percent in Han Chinese to 87 percent in Tibetans, was associated with lower red blood cell count and lower hemoglobin levels in Tibetans. That variation occurred near a gene called EPAS1, which earlier studies suggest is involved in regulating hemoglobin in the blood as a response to oxygen levels. The mutation may be in a transcription factor that regulates the activity of EPAS1.

Tibetans carrying only one allele with this mutation had about the same hemoglobin concentration as Han Chinese, but those with two mutated alleles had significantly lower hemoglobin concentration. However, they all have about the same oxygen concentration in the blood. For some reason, individuals with two copies of the mutation function well in high altitude with relatively low hemoglobin concentration in their blood. The mutation seems to provide an alternative inborn mechanism for dealing with the low oxygen levels, Nielsen said.

Other strongly selected variants were near the genes for the fetal and adult versions of the globin genes, which produce the structural proteins of hemoglobin.

Two other genes showing a dramatic shift in frequency have been linked to anemia, while several other genes have been linked to diseases, including schizophrenia and epilepsy, possibly caused by low oxygen levels in the womb.

A large team of researchers from BGI contributed to the study, some of whom are also associated with the Graduate University of the Chinese Academy of Sciences.

The research was funded by various Chinese, American and Danish organizations, including the U.S. National Institutes of Health and the National Science Foundation. The sequenced genomes were part of the international 1000 Genomes Project, which now aims to sequence 2,500 human genomes by the end of 2011.

Extinction of Woolly Mammoth, Saber-Toothed Cat May Have Been Caused by Human Predators

A new analysis of the extinction of woolly mammoths and other large mammals more than 10,000 years ago suggests that they may have fallen victim to the same type of "trophic cascade" of ecosystem disruption that scientists say is being caused today by the global decline of predators such as wolves, cougars, and sharks.
In each case the cascading events were originally begun by human disruption of ecosystems, a new study concludes, but around 15,000 years ago the problem was not the loss of a key predator, but the addition of one -- human hunters with spears.

In a study published in the journal BioScience, researchers propose that this mass extinction was caused by newly-arrived humans tipping the balance of power and competing with major predators such as saber-toothed cats. An equilibrium that had survived for thousands of years was disrupted, possibly explaining the loss of two-thirds of North America's large mammals during this period.

"For decades, scientists have been debating the causes of this mass extinction, and the two theories with the most support are hunting pressures from the arrival of humans, and climate change," said William Ripple, a professor of forest ecosystems and society at Oregon State University, and an expert on the ecosystem alterations that scientists are increasingly finding when predators are added or removed.

"We believe humans indeed may have been a factor, but not as most current theory suggests, simply by hunting animals to extinction," Ripple said. "Rather, we think humans provided competition for other predators that still did the bulk of the killing. But we were the triggering mechanism that disrupted the ecosystem."

In the late Pleistocene, researchers say, major predators dominated North America in an uneasy stability with a wide range of mammals: mammoths, mastodons, ground sloths, camels, horses, and several species of bison. The new study cites previous evidence from carnivore tooth wear and fracture, growth rates of prey, and other factors that suggest that there were no serious shortages of food caused by environmental change 10,000 to 15,000 years ago.

Quite contrary to that, the large herbivores seemed to be growing quickly and just as quickly had their numbers reduced by a range of significant carnivorous predators, not the least of which was lions, dire wolves, and two species of saber-toothed cats. Food was plentiful for herbivores, the system was balanced, but it was dominated by predators.

"When human hunters arrived on the scene, they provided new competition with these carnivores for the same prey," said Blaire Van Valkenburgh, an expert at UCLA on the paleobiology of carnivores, and a co-author with Ripple on this study.

"The humans were also omnivores, and could live on plant foods if necessary," Van Valkenburgh said. "We think this may have triggered a sequential collapse not only in the large herbivores but ultimately their predators as well. Importantly, humans had some other defenses against predation, such as fire, weapons and living in groups, so they were able to survive."

But the driving force in eliminating the large mammals, according to the new theory, was not humans -- they just got the process started. After that, predators increasingly desperate for food may have driven their prey to extinction over long periods of time -- and then eventually died out themselves.

In recent studies in Yellowstone National Park and elsewhere, scientists from OSU and other institutions have explored these "trophic cascades," often caused by the loss or introduction of a single major predator in an ecosystem. With the elimination of wolves from Yellowstone, for instance, the numbers of elk exploded. This caused widespread overgrazing; damage to stream ecosystems; the slow demise of aspen forests; and ultimate effects on everything from trees to beaver, fish, birds, and other life forms. When wolves were re-introduced to Yellowstone, studies are showing that those processes have begun to reverse themselves.

"We think the evidence shows that major ecosystem disruptions, resulting in these domino effects, can be caused either by subtracting or adding a major predator," Ripple said. "In the case of the woolly mammoths and saber-toothed tiger, the problems may have begun by adding a predator, in this case humans."

The new analysis draws on many other existing studies in making its case.

For instance, other research describes this process with a model in modern times in Alaska. There, the allowance of relatively limited human hunting on moose caused wolves to switch some of their predation to sheep, ultimately resulting in a precipitous decline in populations not only of moose but also wolves and sheep.

The loss of species in North America during the late Pleistocene was remarkable -- about 80 percent of 51 large herbivore species went extinct, along with more than 60 percent of important large carnivores. Previous research has documented the growth rates of North American mammoths by studying their tusks, revealing no evidence of reduced growth caused by inadequate food -- thus offering no support for climate-induced habitat decline.

It seems that diverse and abundant carnivores kept herbivore numbers below levels where food becomes limiting. By contrast, the large population of predators such as dire wolves and saber tooth cats caused them to compete intensely for food, as evidenced by heavy tooth wear.

"Heavily worn and fractured teeth are a result of bone consumption, something most carnivores avoid unless prey is difficult to acquire," says Van Valkenburgh.

Trophic cascades initiated by humans are broadly demonstrated, the researchers report. In North America, it may have started with the arrival of the first humans, but continues today with the extirpation of wolves, cougars and other predators around the world. The hunting of whales in the last century may have led to predatory killer whales turning their attention to other prey such as seals and sea otters -- and the declines in sea otter populations has led to an explosion of sea urchins and collapse of kelp forest ecosystems.

"In the terrestrial realm, it is important that we have a better understanding of how Pleistocene ecosystems were structured as we proceed in maintaining and restoring today's ecosystems," the researchers wrote in their conclusion. "In the aquatic realm, the Earth's oceans are the last frontier for megafaunal species declines and extinctions."

"The tragic cascade of species declines due to human harvesting of marine megafauna happening now may be a repeat of the cascade that occurred with the onset of human harvesting of terrestrial megafauna more than 10,000 years ago. This is a sobering thought, but it is not too late to alter our course this time around in the interest of sustaining Earth's ecosystems."

3,200-Year-Old Bronze Tablet Identified as Battle Chariot Linchpin

A 3,200-year-old round bronze tablet with a carved face of a woman, found at the El-ahwat excavation site near Katzir in central Israel, is part of a linchpin that held the wheel of a battle chariot in place. This was revealed by scientist Oren Cohen of the Zinman Institute of Archaeology at the University of Haifa.

"Such an identification reinforces the claim that a high-ranking Egyptian or local ruler was based at this location, and is likely to support the theory that the site is Harosheth Haggoyim, the home town of Sisera, as mentioned in Judges 4-5," says Prof. Zertal.

The El-ahwat site, near Nahal 'Iron, was exposed by a cooperative delegation excavating there during 1993-2000 from the Universities of Haifa and Cagliari (Sardinia), headed by Prof. Zertal. The excavated city has been dated back to the end of the Bronze Age and early Iron Age (13th-12th centuries B.C.E.). The city's uniqueness -- its fortifications, passageways in the walls, and rounded huts -- made it foreign amidst the Canaanite landscape.

Prof. Zertal has proposed that based on these unusual features, the site may have been home to the Shardana tribe of the Sea-Peoples, who, according to some researchers, lived in Harosheth Haggoyim, Sisera's capital city. The city is mentioned in the Bible's narratives as Sisera's capital, and it was from there that the army of chariots set out to fight the Israelites, who were being led by Deborah the prophetess and Barak, son of Avinoam. The full excavation and its conclusions have been summarized in Prof. Zertal's book "Sisera's Secret, A Journey following the Sea-Peoples and the Song of Deborah" (Dvir, Tel Aviv, 2010 [Hebrew]).

One of the objects uncovered at the site remained masked in mystery. The round, bronze tablet, about 2 cm. in diameter and 5 mm thick, was found in a structure identified as the "Governor's House." The object features a carved face of a woman wearing a cap and earrings shaped as chariot wheels. When uncovered in 1997, it was already clear that the tablet was the broken end of an elongated object, but Mr. Cohen, who included the tablet in the final report of the excavations, did not manage to find its parallel in any other archaeological discoveries.

Now, 13 years later, the mystery has been solved. When carrying out a scrutinizing study of ancient Egyptian reliefs depicting chariot battles, Mr. Cohen discerned a unique decoration: the bronze linchpins fastening the chariot wheels were decorated with people's faces -- of captives, foreigners and enemies of Egypt. He also noticed that these decorations characterized those chariots that were used by royalty and distinguished people.

"This identification enhances the historical and archaeological value of the site and proves that chariots belonging to high-ranking individuals were found there. It provides support for the possibility, which has not yet been definitively established, that this was Sisera's city of residence and that it was from there that the chariots set out on their way to the battle against the Israelite tribes, located between the ancient sites of Taanach and Megiddo," Prof. Zertal concludes.

Complex, Multicellular Life from Over Two Billion Years Ago Discovered

The discovery in Gabon of more than 250 fossils in an excellent state of conservation has provided proof, for the first time, of the existence of multicellular organisms 2.1 billion years ago. This finding represents a major breakthrough: until now, the first complex life forms (made up of several cells) dated from around 600 million years ago.
These new fossils, of various shapes and sizes, imply that the origin of organized life is a lot older than is generally admitted, thus challenging current knowledge on the beginning of life. These specimens were discovered and studied by an international (1) multidisciplinary team of researchers led by Abderrazak El Albani of the Laboratoire "Hydrogéologie, Argiles, Sols et Altérations" (CNRS/Université de Poitiers) (2). Their work, due to be published in Nature on 1st July, will feature on the cover of the journal.

The first traces of life appeared in the form of prokaryotic organisms, in other words organisms without a nucleus, around three and a half billion years ago. Another major event in the history of life, the "Cambrian explosion" some 600 million years ago, marked a proliferation in the number of living species. It was accompanied by a sudden rise in oxygen concentration in the atmosphere. What happened between 3.5 billion and 600 million years ago though? Scientists have very little information about this era, known as the Proterozoic. Yet, it is during this crucial period that life diversified: to the prokaryotes were added the eukaryotes, single or multicelled organisms endowed with a more complex organization and metabolism. These large-sized living beings differ from prokaryotes by the presence of cells possessing a nucleus containing DNA.

While studying the paleo-environment of a fossil-bearing site situated near Franceville in Gabon in 2008, El Albani and his team unexpectedly discovered perfectly preserved fossil remains in the 2.1 billion-year-old sediments. They have collected more than 250 fossils to date, of which one hundred or so have been studied in detail. Their morphology cannot be explained by purely chemical or physical mechanisms. These specimens, which have various shapes and can reach 10 to 12 centimeters, are too big and too complex to be single-celled prokaryotes or eukaryotes. This establishes that different life forms co-existed at the start of the Proterozoic, as the specimens are well and truly fossilized living material.

To demonstrate this, the researchers employed cutting-edge techniques that allowed them to define the nature of the samples and to reconstruct their environment. An ion probe capable of measuring the content of sulfur isotopes made it possible to map the relative distribution of organic matter precisely. This matter is what remains of the living organism, which has been transformed into pyrite (a mineral formed of iron disulfide) during fossilization. This helped the researchers to distinguish the fossils from the Gabonese sediment (made of clay). In addition, using an ultra-sophisticated, high-resolution 3D scanner (also known as X-ray microtomograph), they were able to reconstitute the samples in three dimensions and, in particular, assess their degree of internal organization in great detail, without compromising the integrity of the fossils, since the method is non-invasive. The clearly defined and regular shape of these fossils points to a degree of multicellular organization. These organisms lived in colonies: more than 40 specimens per half square meter were sometimes collected. Consequently, they constitute the oldest multicellular eukaryotes ever described to date.

By studying the sedimentary structures of this site, which is remarkable both for its richness and quality of conservation, the scientists have shown that these organisms lived in a shallow marine environment (20 to 30 meters), often calm but periodically subjected to the combined influence of tides, waves and storms. In order to be able to develop 2.1 billion years ago and become differentiated to a degree never attained previously, the authors suggest that these life forms probably benefited from the significant but temporary increase in oxygen concentration in the atmosphere, which occurred between 2.45 and 2 billion years ago. Then, 1.9 billion years ago, the level of oxygen in the atmosphere fell suddenly.

Until now, it has been assumed that organized multicellular life appeared around 0.6 billion years ago and that before then the Earth was mainly populated by microbes (viruses, bacteria, parasites, etc.). This new discovery moves the cursor of the origin of multicellular life back by 1.5 billion years and reveals that cells had begun to cooperate with each other to form more complex and larger structures than single-celled organisms. Several research avenues now need to be explored: understanding the history of the Gabonese basin and why the necessary conditions were gathered to enable this organized and complex life to exist; further exploring the site to enhance the collection of fossils; but also comparing the history of the Earth's oxygenation with the mineralization of clays. The most urgent task, however, remains the protection of this exceptional site.

Notes:

(1) Made up of around twenty researchers from sixteen different institutions.

(2) With the participation, in France, of the following institutions: the Centre de Microtomographie de l'Université de Poitiers, the Unité "Histoire Naturelle de l'Homme Préhistorique" (CNRS/MNHN), the company "Etudes Recherches Matériaux" of the CRI Biopole de Poitiers, the Unité "Géosciences Rennes" (CNRS/Université de Rennes), BRGM (French Geological Survey), the Laboratoire d'Hydrologie et de Géochimie de Strasbourg (CNRS/Université de Strasbourg), the Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements (CNRS/MNHN/UPMC) and the Laboratoire Géosystèmes (CNRS/Université Lille 1/Université d'Amiens).

Human-Made Global Warming Started With Ancient Hunters

Even before the dawn of agriculture, people may have caused the planet to warm up, a new study suggests.
Mammoths used to roam modern-day Russia and North America, but are now extinct -- and there's evidence that around 15,000 years ago, early hunters had a hand in wiping them out. A new study, accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union (AGU), argues that this die-off had the side effect of heating up the planet.

"A lot of people still think that people are unable to affect the climate even now, even when there are more than 6 billion people," says the lead author of the study, Chris Doughty of the Carnegie Institution for Science in Stanford, California. The new results, however, "show that even when we had populations orders of magnitude smaller than we do now, we still had a big impact."

In the new study, Doughty, Adam Wolf, and Chris Field -- all at Carnegie Institution for Science -- propose a scenario to explain how hunters could have triggered global warming.

First, mammoth populations began to drop -- both because of natural climate change as the planet emerged from the last ice age, and because of human hunting. Normally, mammoths would have grazed down any birch that grew, so the area stayed a grassland. But if the mammoths vanished, the birch could spread. In the cold of the far north, these trees would be dwarfs, only about 2 meters (6 feet) tall. Nonetheless, they would dominate the grasses.

The trees would change the color of the landscape, making it much darker so it would absorb more of the Sun's heat, in turn heating up the air. This process would have added to natural climate change, making it harder for mammoths to cope, and helping the birch spread further.

To test how big of an effect this would have on climate, Field's team looked at ancient records of pollen, preserved in lake sediments from Alaska, Siberia, and the Yukon Territory, built up over thousands of years. They looked at pollen from birch trees (the genus Betula), since this is "a pioneer species that can rapidly colonize open ground following disturbance," the study says. The researchers found that around 15,000 years ago -- the same time that mammoth populations dropped, and that hunters arrived in the area -- the amount of birch pollen started to rise quickly.

To estimate how much additional area the birch might have covered, they started with the way modern-day elephants affect their environment by eating plants and uprooting trees. If mammoths had effects on vegetation similar to those of modern elephants , then the fall of mammoths would have allowed birch trees to spread over several centuries, expanding from very few trees to covering about one-quarter of Siberia and Beringia -- the land bridge between Asia and Alaska. In those places where there was dense vegetation to start with and where mammoths had lived, the main reason for the spread of birch trees was the demise of mammoths, the model suggests.

Another study, published last year, shows that "the mammoths went extinct, and that was followed by a drastic change in the vegetation," rather than the other way around, Doughty says. "With the extinction of this keystone species, it would have some impact on the ecology and vegetation -- and vegetation has a large impact on climate."

Doughty and colleagues then used a climate simulation to estimate that this spread of birch trees would have warmed the whole planet more than 0.1 degrees Celsius (0.18 degrees Fahrenheit) over the course of several centuries. (In comparison, the planet has warmed about six times more during the past 150 years, largely because of people's greenhouse gas emissions.)

Only some portion -- about one-quarter -- of the spread of the birch trees would have been due to the mammoth extinctions, the researchers estimate. Natural climate change would have been responsible for the rest of the expansion of birch trees. Nonetheless, this suggests that when hunters helped finish off the mammoth, they could have caused some global warming.

In Siberia, Doughty says, "about 0.2 degrees C (0.36 degrees F) of regional warming is the part that is likely due to humans."

Earlier research indicated that prehistoric farmers changed the climate by slashing and burning forests starting about 8,000 years ago, and when they introduced rice paddy farming about 5,000 years ago. This would suggest that the start of the so-called "Anthropocene" -- a term used by some scientists to refer to the geological age when human beings began shaping the entire planet -- should be dated to several thousand years ago.

However, Field and colleagues argue, the evidence of an even earlier human-made global climate impact suggests the Anthropocene could have started much earlier. Their results, they write, "suggest the human influence on climate began even earlier than previously believed, and that the onset of the Anthropocene should be extended back many thousands of years."

This work was funded by the Carnegie Institution for Science and NASA.

Unpeeling Atoms and Molecules from the Inside out

The first published scientific results from the world's most powerful hard X-ray laser, located at the Department of Energy's SLAC National Accelerator Laboratory, show its unique ability to control the behaviors of individual electrons within simple atoms and molecules by stripping them away, one by one -- in some cases creating hollow atoms.
These early results -- one published June 30, the other the week before -- describe in great detail how the Linac Coherent Light Source's intense pulses of X-ray light change the very atoms and molecules they are designed to image. Controlling those changes will be critical to achieving the atomic-scale images of biological molecules and movies of chemical processes that the LCLS is designed to produce.

In a report published in the July 1 issue of Nature, a team led by Argonne National Laboratory physicist Linda Young describes how they were able to tune LCLS pulses to selectively strip electrons, one by one, from atoms of neon gas. By varying the photon energies of the pulses, they could do it from the outside in or -- a more difficult task -- from the inside out, creating so-called "hollow atoms."

"Until very recently, few believed that a free-electron X-ray laser was even possible in principle, let alone capable of being used with this precision," said William Brinkman, director of DOE's Office of Science. "That's what makes these results so exciting."

Young, who led the first experiments in October with collaborators from SLAC and five other institutions, said, "No one has ever had access to X-rays of this intensity, so the way in which ultra-intense X-rays interact with matter was completely unknown. It was important to establish these basic interaction mechanisms."

SLAC's Joachim Stöhr, director of the LCLS, said, "When we thought of the first experiments with LCLS ten years ago, we envisioned that the LCLS beam may actually be powerful enough to create hollow atoms, but at that time it was only a dream. The dream has now become reality."

In another report, published June 22 in Physical Review Letters, a team led by physicist Nora Berrah of Western Michigan University -- the third group to conduct experiments at the LCLS -- describes the first experiments on molecules. Her group also created hollow atoms, in this case within molecules of nitrogen gas, and found surprising differences in the way short and long laser pulses of exactly the same energies stripped and damaged the nitrogen molecules.

"We just introduced molecules into the chamber and looked at what was coming out there, and we found surprising new science," said Matthias Hoener, a postdoctoral researcher in Berrah's group at WMU and visiting scientist at Lawrence Berkeley National Laboratory who was first author of the paper. "Now we know that by reducing the pulse length, the interaction with the molecule becomes less violent. "

While the first experiments were designed to see what the LCLS can do and how its ultra-fast, ultra-bright pulses interact with atoms and molecules, they also pave the way for more complex experiments to come. Its unique capabilities make the LCLS a powerful tool for research in a wide range of fields, including physics, chemistry, biology, materials and energy sciences.

The LCLS forms images by scattering X-ray light off an atom, molecule or larger sample of material. Yet when the LCLS X-rays are tightly focused by mirrors, each powerful laser pulse destroys any sample it hits. Since certain types of damage, like the melting of a solid, are not instantaneous and only develop with time, the trick is to minimize the damage during the pulse itself and record the X-ray snapshot with a camera before the sample disintegrates.

Both teams found that the shorter the laser pulse, the fewer electrons are stripped away from the atom or molecule and the less damage is done. And both delved into the detailed mechanisms behind that damage.

Atoms are a little like miniature solar systems, with their electrons orbiting at various distances from the nucleus in a sort of quantum fuzz. To make things simpler, scientists describe the electrons as orbiting in "shells" at specific distances from the nucleus. The innermost shell contains up to two electrons, the next one up to eight, the third one up to 18, and so on.

Since they're closest to the positively charged nucleus, the two innermost electrons are generally the hardest to wrest away. But they also most readily absorb photons of X-ray light, and so are the most vulnerable to getting stripped away by intense X-rays.

Although previous experiments with intense optical lasers had stripped neon atoms of most of their electrons, Young's was the first to discover how ultra-intense X-ray lasers do this. At low photon energies, the outer electrons are removed, leaving the inner electrons untouched. However, at higher photon energies, the inner electrons are the first to be ejected; then the outer electrons cascade into the empty inner core, only to be kicked out by later parts of the same X-ray pulse. Even within the span of a single pulse there may be times when both inner electrons are missing, creating a hollow atom that is transparent to X-rays, Young said.

"This transparency associated with hollow atoms could be a useful property for future imaging experiments, because it decreases the fraction of photons doing damage and allows a higher percentage of photons to scatter off the atom and create the image," Young said. She said application of this phenomenon will also allow researchers to control how deeply an intense X-ray pulse penetrates into a sample.

Berrah's team bombarded puffs of nitrogen gas with laser pulses that ranged in duration from about four femtoseconds, or quadrillionths of a second, to 280 femtoseconds. No matter how short or long it was, though, each pulse contained the same amount of energy in the form of X-ray light; so you might expect that they would have roughly the same effects on the nitrogen molecules.

But to the team's surprise, that was not the case, Hoener said. The long pulses stripped every single electron from the nitrogen molecules, starting with the ones closest to the nucleus; the short ones stripped off only some of them.

Their report attributes this to the "frustrated absorption effect": Since the molecule's electrons are preferentially stripped from the innermost shells, there is simply not enough time during a short pulse for the molecule's outermost electrons to refill the innermost shells and get kicked out in turn.

With all this activity going on inside the atom, scientists have a new way to explore atomic structure and dynamics. Further experiments have investigated nanoclusters of atoms, protein nanocrystals and even individual viruses, with results expected to be published in coming months.