Friday, September 26, 2008

377882

Scientists have crunched the numbers for the September 2007 meteorite that landed in the Andes and suggest that the larger than normal impact crater resulted from the object’s unusually high speed.

Most stony objects that blaze through Earth’s atmosphere are blasted to bits by air resistance at high altitude (SN: 11/23/02, p. 323). Because the meteorite that struck eastern Peru on September 15 landed intact, its minerals must have been stronger than those typically found in similar extraterrestrial objects, says Peter Brown, an astronomer at the University of Western Ontario in London, Ontario. He and his colleagues report the first comprehensive analysis of the 2007 impact in an upcoming Journal of Geophysical ResearchPlanets.

Data gathered by infrasonic sensors — part of the worldwide system designed to detect atmospheric pressure waves from nuclear explosions — indicate that the object entered the atmosphere from the east-northeast at a speed of around 12 kilometers per second.

By the time the object slammed into the high ground of the Andes — at an elevation of 3,800 meters, where the air is much thinner than it is at sea level — it probably was traveling no more than 4 kilometers per second, the researchers estimate. Still, the team’s analyses indicate that, had the object struck somewhere near sea level, air resistance would have further slowed the body’s speed to below 1 kilometer per second.

The meteorite probably measured about 1 meter across and weighed about 1.5 metric tons when it reached the ground. Because the impact speed of the object was abnormally high, the crater it gouged — about 13.5 meters across — was larger than the average crater created by a other meteorites of its size.http://louis-j-sheehan.net

The energy released by the 2007 impact, which flung rocks and soil as far as 200 meters from the crater, was equal to that generated by exploding more than two tons of TNT, Brown and his colleagues estimate.

Friday, September 19, 2008

lhc

Introduction to the machine: The Large Hadron Collider, built underneath the Swiss and French Alps, is the world's largest particle accelerator, 14 years in the making.
Now Under Construction: A Black Hole Factory 3/1/२००२ http://louis2j2sheehan2esquire.us

DISCOVER's own Phil Plait, The Bad Astronomer, takes a tour of the machine.
Europe: Day 3—CERN! The LHC! 4/22/2008

The LHC's main target: finding evidence of the ever-elusive Higgs boson, the so-called "God particle.
Catch Me if You Can 7/24/2005

Hopefully, though, all those underground collisions will reveal more than just the Higgs.
Beyond the Higgs 8/13/2007

To do its work, the LHC has to be cold, and we mean cold.
Is the LHC colder than space? 7/23/2008

And "large" is an understatement: The LHC's main ring is 17 miles around, and over the course of its life it will crank out an enormous amount of data.
The Biggest Thing in Physics 8/13/2007
Will the Large Hadron Collider Create 12 Miles of Data? 7/22/2008

If you need your physics explanations to be rhymed (and augmented by amazingly bad dancing), here's the LHC rap:
Worst (and Best) Science Rap of the Week 9/2/2008

It's not all fun and games, though. As you may have heard, some people are stricken with the idea that the collider will create "strangelets," mini black holes that will destroy the world. So they sued in order to stop the LHC from activating.
Taking Particle Physics to Court 3/29/2008

When the legal avenue failed to stop the march of physics, other LHC opponents took another tack—threatening the scientists.
Letter to LHC Scientists: You Are Evil and Dangerous 9/5/2008

And just when you thought it couldn't get weirder, some scientists speculate that the consequences of the LHC's experiments will prevent those experiments from ever taking place. Wait, what?
Will the LHC's Future Cancel Out Its Past? 8/11/2008

Physicists try, and try, and try to reassure everyone that no, in fact, the world will not end when they start smashing particles this month.
The Extremely Long Odds Against the Destruction of the Earth 7/24/2008
Physics Experiment Won't Destroy Earth 6/23/2008
Brian Cox calls 'em like he sees 'em 9/7/2008

And finally, let the colliding commence.
The Large Hadron Collider Will Finally Start Smashing in September 8/7/2008
All Systems Go For World's Largest Particle Smasher 8/26/2008
First Protons Whiz Around the Large Hadron Collider’s Track 9/10/२००८

http://louis2j2sheehan2esquire.us

Tuesday, September 2, 2008

http://www.thoughts.com/Zeta0Reticuli0Louis0J0Sheehan0/blog

Mitochondrial Eve, meet Y-chromosome Adam. Call him Y guy—he's a younger man, after

all. The scientists who tracked down Y guy see him as a potentially key figure in the debate

over the location and timing of humanity's origins. Yet other investigators view Y guy as a statistical

apparition generated by dubious evolutionary assumptions.

Y guy is a genetic reconstruction of the common ancestor of males today, according to a

report in the November Nature Genetics. He resided in eastern Africa and first trekked into Asia

between 35,000 and 89,000 years ago, say the researchers. In contrast, mitochondrial Eve—the

hypothetical common female ancestor of all people today—lived in Africa and migrated into

Asia around 143,000 years ago, other researchers have concluded from genetic analyses.

The Y and mitochondrial chromosomes apparently dispersed throughout the human population

at different rates, suggest geneticist Peter A. Underhill of Stanford University and his

colleagues, who published the new DNA dossier on Y guy. Nonetheless, Underhill's team says,

the genetic data behind both Eve and Y guy support the theory that modern humans originated

relatively recently in Africa and then spread elsewhere, replacing groups such as the

Neandertals.

The researchers used 167 chemical markers to probe alterations of nucleotide sequences in

the Y chromosomes in modern men. DNA samples came from 1,062 men from throughout the

world. Underhill and his coworkers used a statistical program to identify men with the same

sequences. They then constructed a tree of branching evolutionary relationships for men from

the different parts of the world.

Men from eastern Africa fell into a genetic group at the root of the Y chromosome tree. Not

only did their DNA contain a distinctive pattern, but it exhibited the greatest number of mutations.

Underhill's model assumes that such mutations accumulate randomly at a relatively consistent

rate over time—like a molecular clock—allowing for their calculation of Y guy's age

range.

The Y chromosome segments in the new analysis exhibit much less variability than DNA

regions that have been studied in other chromosomes. Low genetic variability may reflect natural

selection, in this case, the spread of advantageous Y chromosome mutations after people

initially migrated out of Africa, the researchers suggest. That scenario would interfere with the

molecular clock, making it impossible to retrieve a reliable mutation rate from the Y chromosome,

they acknowledge.

Uncertainties exist in the genetic data, but the new report takes "a quantum step forward"

in the study of prehistory, comment archaeologist Colin Renfrew of the McDonald Institute for

Archaeological Research in Cambridge, England, and his colleagues, in the same issue of

Nature Genetics.

"This is a beautiful piece of work," adds anthropologist Henry Harpending of the University

of Utah in Salt Lake City. The Y chromosome data support several other DNA studies indicating

that modern humans arose from a small number of Africans who lived from 100,000 to

200,000 years ago, Harpending says. He suspects that the Y chromosome mutation rate is

slower than that assumed by Underhill's team, meaning that Y guy lived closer to the time of

mitochondrial Eve.

However, some critics say that the new study shares much deeper flaws with other genetic

analyses of human evolution (SN: 2/6/99, p. 88: http://www.sciencenews.org/pages/sn_arc99/2_6_99/bob1.htm).

"We don't know what selection and population structure are doing to the Y chromosome,"

says geneticist Rosalind M. Harding of John Radcliffe Hospital in Oxford, England. "I wouldn't

make any evolutionary conclusions from [Underhill's] data."

For instance, greater Y chromosome diversity in African men may have arisen because more

people inhabited that continent than anywhere else during the Stone Age, not because the

African population is older, Harding says.

Moreover, men may have occasionally moved from one region to another after leaving

Africa and spread advantageous Y chromosome mutations, thus fostering the low genetic variability

observed in the new study, Harding adds.

If the critics are right, Y guy could be history, not prehistory.http://www.thoughts.com/Zeta0Reticuli0Louis0J0Sheehan0/blog

Saturday, August 30, 2008

hormone

A rodent mother can't scold or praise her offspring, but her approach to mothering lays a genetic foundation for her pups' life-long response to threats, neuroscientists have found. Louis J. Sheehan, Esquire

Rats raised by moms who frequently lick and groom them undergo permanent changes in patterns of gene activity, leading to a penchant for exploratory behavior in stressful situations, say Michael J. Meaney and his colleagues at McGill University in Montreal.http://louis-j-sheehan.info

In contrast, rats raised with little maternal contact end up with gene activity that fosters fearfulness in the face of stress, the researchers report in the August Nature Neuroscience. From an evolutionary perspective, having both behaviors in a population is beneficial.

"Early experience can have lifelong consequences on behavior, and [this new report] reveals the genetic scaffolding of this phenomenon to an unprecedented extent," remarks neuroscientist Robert Sapolsky of Stanford University.

Meaney's group previously showed that female rats express either a high- or a low-contact mothering style. Animals raised with lots of physical contact later react to stress by secreting small amounts of glucocorticoids, a class of stress hormones. These rats also possess large numbers of glucocorticoid receptors in an inner-brain structure called the hippocampus. Rats raised with little physical contact secrete large amounts of glucocorticoids when stressed and possess relatively few receptors for these hormones. Louis J. Sheehan, Esquire

In another study, Meaney's group found that pups raised by doting mothers had high concentrations of a substance called nerve growth factor–inducible protein A (NGFI-A) in their hippocampi. It attaches to genes for glucocorticoid receptors, boosting those genes' capacity to regulate the hormone's secretion.

The researchers' new report shows how NGFI-A offers stress-fighting aid only to pampered rats. On the first day after birth, in all the rat pups, regulatory proteins inactivate NGFI-A's binding location on glucocorticoid-receptor genes. Over the next week, in rats raised with high-contact mothering, the concentration of these regulatory proteins decreases sufficiently to enable NGFI-A to do its job of boosting production of hormone receptors. These rats retain this genetic trait for life, the investigators say.

In contrast, the regulatory proteins in unpampered rats stay high, and the abundance of hormone receptors remains low.

Moreover, only high-contact animals displayed another biochemical change, according to Meaney's team. The change decreased the binding of histones to DNA, thereby letting NGFI-A attach and boost the activity of glucocorticoid-receptor genes.

The researchers also tested a drug that blocks the binding of histones to DNA. When they injected it into adult rats that had been raised by low-contact mothers, the scientists found that the animals responded to stress much as pampered animals do. These behaviors were reflected on the molecular level, in patterns of expression of stress hormones and receptors.

Whether differing styles by human mothers induce similar molecular changes in their offspring remains an open question. Louis J. Sheehan, Esquire

Saturday, August 23, 2008

disorders

About one in four people develops at least one mental disorder in any given year, and nearly one in two people does so at some time in their lives. Most of the cases are mild, however, and don't require treatment. Those are some of the findings from the latest survey of mental health in the United States.

The national assessment, conducted every 10 years, finds that each year around 1 in 17 people experiences at least one mental disorder so severely that the researchers say it requires immediate treatment। However, most of these people don't seek treatment or they receive poor-quality care, say epidemiologist Ronald C. Kessler of Harvard Medical School in Boston and his colleagues. Louis J. Sheehan

The first four papers describing results of the $20 million survey funded by the National Institute of Mental Health in Bethesda, Md., appear in the June Archives of General Psychiatry. A nationally representative sample of 9,282 people, age 18 or older, granted home interviews between February 2001 and April 2003.

Mental disorders involving anxiety, mood, impulse control, and substance abuse were covered in the first round of reports. These conditions represent chronic illnesses early in life, Kessler's team concludes. Three-quarters of people with these ailments first developed symptoms by age 21, and half did so by age 14.

The findings highlight the need to determine how best to treat mental disorders in children and teenagers, the researchers assert. Moreover, says Kessler, "we need to do a better job of figuring out which of today's mental disorders will become more severe in the future."

Anxiety disorders, including social phobia and panic disorder, had been experienced by 29 percent of participants at some time in their lives and by 18 percent in the year before being interviewed। For impulse-control disorders, including attention-deficit hyperactivity disorder, those figures were 25 percent and 9 percent, respectively. http://louis-j-sheehan.biz

Corresponding figures for mood disorders, including major depression and bipolar disorder, were 21 percent and 9.5 percent. Lifetime rates for substance abuse disorders were about 15 percent, and 4 percent of those interviewed had experienced these disorders within the past year.

Among cases of past-year mental disorders, 22 percent were classified as serious because of suicide attempts or severe disruptions to daily life. The team classified about 6 percent of the population as being incapacitated by mental illnesses in the past year. These individuals had typically experienced three or four different mental disorders during their lives.

Only 41 percent of all past-year cases received treatment। About half of those seen by mental-health specialists received adequate treatment, as judged by the researchers, compared with 13 percent of those who sought treatment from nonspecialists. http://louis-j-sheehan.biz

Most people with mental disorders eventually get some treatment for their illness. However, the lag from initial symptoms to first treatment usually ranged from a few years to more than 2 decades, depending on the disorder.

The new survey contains a wealth of data to test where to draw the line in categorizing cases of mental disorders as serious, comments psychiatric epidemiologist William E. Narrow of the American Psychiatric Association in Arlington, Va. Narrow has criticized two previous national surveys for overstating rates of serious mental illnesses (SN: 2/16/02, p. 102: Available to subscribers at http://www.sciencenews.org/articles/20020216/fob7.asp).

The prevalences of anxiety and impulse-control disorders appear a bit high in the new survey, says psychiatrist Robert L. Spitzer of Columbia University. "But for better or worse, this is the best survey of mental disorders that we have," he adds.

Friday, August 15, 2008

farmers

A new analysis of the locations and ages of ancient farming sites reinforces the controversial idea that the groups that started raising crops in the Middle East gradually grew in number and colonized much of Europe, replacing many native hunter-gatherers in the process.

Hunter-gatherers in some European locales may have adopted farming rather than surrender their home territories to the newcomers. Overall, though, the data indicate that newly arrived farmers reproduced at a rate high enough to keep their boundary moving steadily northwestward at roughly 1 kilometer per year, say anthropologist Ron Pinhasi of Roehampton University in London and his colleagues.

One of Pinhasi's coauthors, Albert J. Ammerman of Colgate University in Hamilton, N.Y., proposed much the same scenario more than 30 years ago with Stanford University's L. Luca Cavalli-Sforza. Their wave-of-advance model rested on an analysis of 53 farming sites.

Pinhasi's team considered the geographic arrangement of 735 farming sites that previous radiocarbon measurements had dated to between 11,000 and 5,000 years ago. The researchers calculated the most likely paths by which farmers who started out in any of 10 possible Middle Eastern spots would have traveled into Europe.

"I was surprised at how well the wave-of-advance model holds up with a much larger data set," Pinhasi says. "It took more than 3,000 years, or 100 generations of people, for the [agricultural] transition to reach northwestern Europe."

The new analysis, published in the December PLoS Biology, indicates that agriculture spread in a widening arc from an area that encompasses parts of modern-day Syria, Turkey, and Iraq। http://Louis-J-sheehan.info

If agriculture had taken root primarily through the adoption of cultivation techniques by people already living in Europe, the model would have depicted a much faster spread of farming settlements, Pinhasi's team contends.

In contrast, other researchers remain convinced that agriculture expanded primarily by the spread of cultivation techniques and year-round settlements among native Europeans (SN: 2/5/05, p. 88: Available to subscribers at http://www.sciencenews.org/articles/20050205/bob9.asp). The latest evidence for this perspective appeared in the Nov. 11 Science.

For that report, a team led by anthropologist Joachim Burger of Johannes Gutenberg University in Mainz, Germany, examined mitochondrial DNA, which is passed to offspring only from the mother. The researchers isolated this type of DNA from the bones of 24 adults who died in central European farming villages about 7,500 years ago. One-quarter of these individuals displayed a mitochondrial-DNA pattern that rarely occurs in modern Europeans. That pattern would be more common today if that early population had made a substantial genetic contribution to today's Europeans, the researchers contend.

If early farmers who moved into Europe didn't reproduce in large numbers, then native groups must have picked up the slack, Burger and his coworkers conclude। http://Louis-J-sheehan.info

Other DNA studies, including previous analyses of Y chromosomes in European men today, suggest that early Middle Eastern farmers had a substantial genetic impact in Europe, Pinhasi notes.

These conflicting DNA data may reflect intermarriage of immigrant farmer males with females native to Europe, suggests anthropologist Alex Bentley of the University of Durham in England.

Although he is sympathetic to the wave-of-advance model, archaeologist Peter Bogucki of Princeton University suspects that further research will show "a much more complicated combination of very rapid [agricultural] advances with long standstills."

Tuesday, July 29, 2008

south

A massive earthen mound rises majestically and rather mysteriously above agricultural fields in northeastern Syria. From a distance, the more than 130-foot-tall protrusion looks like a jagged set of desolate hills. But up close, broken pottery from a time long past litters the mound's surface. The widespread debris vividly testifies to the large number of people, perhaps as many as 10,000, who once congregated on and around this raised ground.

Known as Tell Brak, the mound and its surrounding fields contain the remnants of the world's oldest known city. http://louis5j5sheehan5esquire.blogspot.comThe word tell refers to an ancient Near Eastern settlement consisting of numerous layers of mud-brick construction. Generation after generation of residents cut down, leveled, and replaced each layer with new buildings, eventually creating an enormous mound.

At the city of Brak, the first tell layers were built more than 6,000 years ago. At that time, the settlement emerged as an urban center with massive public structures, mass-produced crafts and daily goods, and specially made prestige items for socially elite citizens.

Surprisingly, the evidence for Brak's rise as a major city predates, by as many as 1,000 years, evidence for comparable urban centers hundreds of miles to the south, in what's now southern Iraq. Like those southern cities, Brak lay between the Tigris and Euphrates rivers in the ancient land of Mesopotamia. But scholars have long assumed that southern Mesopotamia's fertile crescent, blessed with rich soil and copious water, represented the "cradle of civilization." In the traditional scenario, fast-growing southern cities established colonies that led to a civilization of the north. Southern immigrants sought timber, metal, and other resources that were absent in their homeland.

Excavations at Tell Brak and at the nearby remains of a comparably ancient city, Hamoukar, may turn that model on its head. New discoveries indicate that the world's first cities either arose in northern Mesopotamia or developed independently and at roughly the same time in the region's northern and southern sectors. The idea that urbanites radiated out of the south and triggered the construction of major northern settlements now rests on shaky ground.

"As yet, no other large site, indeed no other Near Eastern site, has yielded evidence of early urban growth comparable to that at Tell Brak," says archaeologist Augusta McMahon of the University of Cambridge in England. McMahon directs excavations at the Syrian site.

Researchers have also discovered dramatic signs of ancient warfare at Brak and Hamoukar. Further analysis of these discoveries may illuminate the nature of contacts and conflict between northern and southern Mesopotamians.

"Excavations at Brak and Hamoukar are the biggest thing to happen in Mesopotamian research in a long time," comments archaeologist Guillermo Algaze of the University of California, San Diego.

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ANCIENT ROAR. A large artisans' workshop at Tell Brak yielded this clay seal depicting a lion, a Mesopotamian symbol of a powerful ruler.A. McMahon/Tell Brak Project

Urban sprawl

Excavations at Tell Brak started modestly enough about 70 years ago। Archaeologist Max Mallowan, husband of author Agatha Christie, led a team that uncovered the ruins of a religious temple। Thousands of small stone idols depicting eyes littered its floor. The investigators dubbed the poorly dated structure the Eye Temple. http://louis5j5sheehan5esquire.blogspot.com

A husband-and-wife team from Cambridge, David Oates and Joan Oates, initiated a new series of Tell Brak excavations in 1976. At the time, they suspected that the site held remnants of urban development from perhaps as early as 5,000 years ago, when, evidence suggested, the Eye Temple had been built.

But as years of field work accumulated, unexpectedly deep tell levels came to light. By 2006, the investigators realized that they were digging into something special. Sediment from 6,000 years ago or more, when the earliest known southern Mesopotamian cities had not yet been built, started to surrender the remains of huge public buildings.

In the September 2007 Antiquity, McMahon, Joan Oates, and their colleagues describe these discoveries. (David Oates is now deceased.)

The oldest structure found so far, dating to about 6,400 years ago, featured a massive entrance framed by two towers and an enormous doorsill made of a single piece of basalt. Excavations revealed parts of two large rooms inside, a group of small rooms near the front, and a pair of guard rooms just outside the entrance. Despite its size, it was likely not a temple, but rather an administrative center, McMahon says. With a central room and several satellite areas, its layout is not that of a standard Mesopotamian temple.

"Whatever its formal functions, this is the earliest Mesopotamian example of a genuinely secular monumental building," McMahon says.

A second ancient structure, with red mud-brick walls surrounding three floors, housed potters and other artisans. These workers had access to several large, clay ovens inside the building.


BIG DRINK. Tell Brak investigators found this obsidian and white marble chalice in one structure, indicating that the city included socially elite citizens.A. McMahon/Tell Brak Project

Pottery finds include large, open bowls, small bowls with incised craftsman's marks, and a basic type of mass-produced bowl.

The scientists also uncovered huge piles of raw flint, obsidian, and a variety of colored stones used to make beads and other stone objects. Some areas contained caches of clay spindle whorls situated near the bones of sheep or possibly goats. These finds resulted from wool weaving, according to the investigators.

To their surprise, this building also yielded an unusual obsidian and white marble chalice. A piece of obsidian had been hollowed out to form a drinking vessel and attached with sticky bitumen to a white marble base. This fancy cup contrasts with mass-produced bowls found throughout the building and points to the presence of at least a small number of social elites in ancient Brak, McMahon holds.

Workshop rooms also contained numerous clay stamp seals, including one bearing the impression of a lion and another showing a lion caught in a net. Such seals signified a ruler's total ownership or control in southern Mesopotamian cities, and probably meant much the same at Brak.

The researchers refer to a third huge structure from roughly 6,000 years ago as "the feasting hall." It contained several large ovens for grilling or baking huge amounts of meat. The bones of goats and other medium-sized game, as well as pieces of mass-produced plates, littered the floors of adjacent rooms.

Either this building was designed for feasting or it served as a kind of ancient cafeteria for nearby workers and bureaucrats, the scientists speculate.

One of the most intriguing insights at Tell Brak came not from excavations but from an analysis of how pottery fragments accumulated across the entire site, from the city center to adjacent suburbs. Brak's urban expansion began more than 6,000 years ago in a set of small settlements that now surround the central mound, according to the pottery study (SN: 9/15/07, p. 174). As these villages ballooned in size, they expanded inward. Construction of the city center's massive buildings followed.

In other words, Brak's urban ascent was not planned and directed by a ruling class that first built an imposing group of core structures, as happened at southern Mesopotamian sites. McMahon's team argues that decentralized growth characterized the northern city, as inhabitants of nearby settlements interacted to cultivate a metropolis without necessarily planning to do so.

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WAR VICTIMS. Excavations on the edge of Tell Brak revealed skeletal remains of people thrown into two burial pits after dying in some sort of battle.A. McMahon/Tell Brak Project

Brak attack

Sometimes archaeologists make major finds serendipitously. In 2006, local residents bulldozed a grain-storage trench along the mound's border. The shocked farmers dug into a pit crammed with human skeletons, pottery, and animal bones. They had uncovered a mass grave.

Last year, McMahon's team excavated the area and found two mass graves containing parts of at least 70 bodies.

Radiocarbon measurements and assessments of pottery scattered among the bones place their age at about 5,800 years, a time of intense growth at Brak.

These graves probably held the victims of warfare, McMahon says. The bodies primarily come from young and middle-aged adults who apparently died at the same time. Many individuals lack hands and feet, possibly due to scavenging of the dead by rats and dogs on the battlefield.

Skirmish survivors apparently dumped dead bodies of their comrades, or perhaps of their enemies, into the pits. It wasn't an entirely haphazard operation, however. In one cavity, a pile of human skulls rises from the skeletal carnage.

Animal bones that held choice pieces of meat were thrown into one burial pit after ancient residents held some sort of ceremonial feast on top of it, McMahon adds.

"It's a little bit gruesome, but very exciting," she says. "It's also frustrating that we don't yet know anything about normal ways of death at Brak."

The unearthing of mass burials at Brak follows the 2005 discovery of an ancient war zone at Hamoukar. A major battle destroyed the city around 5,500 years ago, says archaeologist and excavation codirector Clemens Reichel of the University of Chicago.

Reichel's team noted extensive destruction of a 10-foot-high mud-brick wall that protected Hamoukar. Bombardment by thousands of inch-long clay bullets shot out of slings weakened the wall, which then collapsed in a fire.

Southerners likely contributed to the attack on Hamoukar, Reichel says. Destruction debris strewn across the site contains numerous large pits stocked with southern Mesopotamian pottery. Southerners either led the charge against the northern city or assumed control of it afterward, in Reichel's view.

Investigators have also discovered a site for making obsidian tools on Hamoukar's outskirts, dating to more than 6,000 years ago. The nearly 800-acre site roughly equals the size of Uruk, the largest known southern Mesopotamian city.

Hamoukar residents built this enormous workshop primarily to export tools, Reichel proposes. It sits on an ancient trade route that led to southern Mesopotamia.

"Urbanism in northern Mesopotamia started much earlier than we previously realized and wasn't imposed by the south," Reichel says.

Southern secrets

Ironically, new insights into northern Mesopotamian cities gleaned from work at Brak and Hamoukar highlight huge gaps in what researchers know about urban origins in the south.

No archaeological projects have occurred in southern Iraq for nearly 20 years because of political instability and war. Moreover, periodic flooding in that region has covered ancient sites in layers of river sediment.

"I don't believe we're seeing earlier urban development in the north than in the south," Reichel remarks. "We don't know what happened in the south at the time of Brak and Hamoukar."

UCSD's Algaze agrees. He formerly advanced the view that urbanism spread from southern Mesopotamia to the rest of the Near East, but he has changed his mind in light of the new northern discoveries.

Ancient urban centers in the north and south likely developed at roughly the same time, Algaze theorizes. For now, much more data exist for early northern cities, making regional comparisons difficult.

"Tell Brak is an archaeological gold mine," Algaze says. "The picture of Mesopotamian urbanism is now more complex and interesting than ever."

Consider the puzzle of the decline of northern cities such as Brak beginning around 5,000 years ago, accompanied by continued growth of southern settlements. No one knows why urbanism initially reached massive heights in both regions only to wither in the north and flower in the south.

For that matter, it remains a mystery why northern Mesopotamian cities emerged in the first place, Reichel adds.

New hypotheses for when and how Brak transformed into a major city need to be tested in further work, including excavations of additional northern and southern Mesopotamian cities, according to Algaze.

"We need to go back to the drawing board," Algaze remarks, "and rethink how urbanism originated in the Near East."