Wednesday, April 14, 2010

Did a change in climate or an extraterrestrial impact bring an end to the beasts and people that roamed the Southwest shortly after the last ice age?

A team of researchers from the University of Arizona has revisited evidence pointing to a cataclysmic event thought by many scientists to have wiped out the North American megafauna – such as mammoths, saber tooth cats, giant ground sloths and Dire wolves – along with the Clovis hunter-gatherer culture some 13,000 years ago. The team obtained their findings following an unusual, multidisciplinary approach and published them in the Proceedings of the National Academy of Sciences (PNAS).

"The idea of an extraterrestrial impact driving the Pleistocene extinction event has recently caused a stir in the scientific community," said C. Vance Haynes, a professor emeritus at UA's School of Anthropology and the department of geosciences, who is the study's lead author. "We systematically revisited the evidence for an impact scenario and discovered it just does not hold up."

Haynes has dedicated his scientific career to the study of the Clovis people – the first well-defined culture in the New World – and discovered many sites with evidence of their presence in Arizona. One of the most prominent and most studied of those sites is the Murray Springs Clovis site in southeastern Arizona, where archaeologists and anthropologists have unearthed hundreds of artifacts such as arrowheads, spear points and stone tools. The site includes the remains of a Clovis hunters' camp close to a mammoth and a bison kill site, allowing the researchers to reconstruct the daily life of the Clovis culture to a certain extent.

When the last ice age came to an end approximately 13,000 years ago and the glaciers covering a large portion of the North American continent began melting and retreating toward the north, a sudden cooling period known as the "Big Freeze" or, more scientifically, the Younger Dryas, reversed the warming process and caused glaciers to expand again. Even though this cooling period lasted only for 1,300 years, a blink of an eye in geologic timeframes, it witnessed the disappearance of an entire fauna of large mammals.

The big question, according to Haynes, is 'Why did those animals go extinct in a very short geological timeframe?'"

"When you go out and look at the sediments deposited during that time, you see this black layer we call the Black Mat. It contains the fossilized remains of a massive algae bloom, indicating a short period of water table rise and cool climate that kept the moisture in the soil. Below the Black Mat, you find all kinds of fossils from mammoths, bison, mastodons, Dire wolves and so forth, but when you look right above it – nothing."

Scientists have suggested several scenarios to account for the rapid Pleistocene extinction event. Some ascribe it to the rapid shift toward a cooler and dryer during the "Big Freeze," causing widespread droughts.

Haynes disagrees. "We find evidence of big changes in climate throughout the geologic record that were not associated with widespread extinctions."

Others have blamed the demise of the North American megafauna on pathogens brought onto the North American continent by animals from the Old World crossing the Bering Strait. "The disease hypothesis does not hold up well in the light of natural selection and evolution," Haynes said, "because some individuals would have been immune to the pathogens and survived."

The two attempts to account for the mass extinction event prevailing at this point include humans and celestial bodies. Many deem it possible that humans such as the Clovis culture hunted the Pleistocene mammals to extinction, as proposed by UA Professor Emeritus Paul S. Martin.

Alternatively, it is thought that a comet or asteroid slammed into the glaciers covering the Great Lakes area, unleashing firestorms that consumed large portions of vegetation. In addition, the dust and molten rock kicked up high into the atmosphere during the impact could have shrouded the Earth in a nuclear winter-like blanket of airborne dust, blocking sunlight and causing temperatures to plummet.

In the present study, Haynes and his coworkers set out to put the evidence for an impact scenario to the test: Unusually high concentrations of spherical magnetic particles in the soil samples taken at the Murray Springs Clovis site had been interpreted as indication of an extraterrestrial source.

Another hint in this direction was a spike in the Black Mat's iridium content – an element rarely encountered on Earth but quite abundant in meteorites. In addition, the occurrence of nanodiamonds had been suggested as evidence of an extraterrestrial origin. Finally, a supposedly abundant charcoal content in the soil samples had been cited as evidence of widespread wildfires ravaging the land in the aftermath of the impact.

To ensure their samples were comparable, Haynes collected at the same locations in the Black Mat layer as the team proposing the impact scenario: "I sampled where they sampled and at the same times they sampled."

Using highly sensitive and sophisticated analytical methods, Haynes' coworkers at the department of geosciences and UA's Lunar and Planetary Lab then analyzed their samples for the evidence that had been presented in support of the impact scenario.

The team did find abundant magnetic spherules. But where did they come from? Was a meteorite the only possible source?

"Researchers have only begun to study those magnetic spherules recently, so we still don't know much about them," Haynes said. "What we do know is that they occur in exhaust from vehicles and power plants."

To determine whether the magnetic spherules found at Murray Springs could be of terrestrial origin, Haynes followed a tip from UA Geosciences Professor Anthony Jull, who suggested taking a sample of dirt from the rooftop of his house and examining it under the microscope.

Haynes remembers looking at the soil samples on a microscope slide, and "sure enough, there they were – among all the dust and grains and grit, they appeared like tiny, shiny ball bearings."

"We did confirm the other authors' findings that the magnetic spherules are concentrated in the samples at the Clovis site, but when you study the topography on which the sediments were laid down, you immediately see why: Rainwater washed them down into a river bed, where they accumulated over time. Since this is where the samples with the increased spherule content came from, we were not surprised to find more of the spherules there. The samples we took from the slopes do not have higher than normal concentrations of spherules."

What about the charcoal indicating vegetation burning?

"The only places we found charcoal were the campsites of the Clovis people, where they build their fires."

But where could the nanodiamonds come from?

Again, Haynes' colleague, Anthony Jull, had the answer. A common ingredient of cosmic dust, nanodiamonds are constantly raining down onto the earth's surface, rendering them unsuitable as unequivocal evidence of an extraterrestrial impact.

"Something happened 13,000 years ago that we do not understand," said Haynes. "What we can say, though, is that all of the evidence put forth in support of the impact scenario can be sufficiently explained by earthly causes such as climate change, overhunting or a combination of both."

Does this mean the results obtained by Haynes and his coworkers rule out the possibility of a cosmic event?

"No, it doesn't," Haynes said. "It just doesn't make it very likely."

Thursday, April 8, 2010

More On New Homind Species

Two partial skeletons unearthed from a cave in South Africa belong to a previously unclassified species of hominid that is now shedding new light on the evolution of our own species, Homo sapiens, researchers say. The newly documented species, called Australopithecus sediba, was an upright walker that shared many physical traits with the earliest known Homo species—and its introduction into the fossil record might answer some key questions about what it means to be human.

The fossils are between 1.95 and 1.78 million years old, and in this week's issue of Science, the peer-reviewed journal published by AAAS, the nonprofit science society, two reports describe both the physical characteristics of this new Australopithecus species as well as the ancient environment in which it lived and died. The emerging picture is one of a hominid with a bone structure similar to the earliest Homo species, but who employed it more as an Australopithecus, like the famed "Lucy," would have.

These new fossils, however, represent a hominid that appeared approximately one million years later than Lucy, and their features imply that the transition from earlier hominids to the Homo genus occurred in very slow stages, with various Homo-like species emerging first.

"It is not possible to establish the precise phylogenetic position of Australopithecus sediba in relation to various species assigned to early Homo," wrote Lee Berger, a lead author of one of the Science reports. "We can conclude that… this new species shares more derived features with early Homo than any other known australopith species, and thus represents a candidate ancestor for the genus, or a sister group to a close ancestor that persisted for some time after the first appearance of Homo."

Many scientists believe that the human genus Homo evolved from Australopithecus a little more than two million years ago—but the origin has been widely debated, with other experts proposing an evolution from the Kenyanthropus genus. This new Australopithecus sediba species might eventually clear up that debate, and help to reveal our direct human ancestors.

"Before this discovery, you could pretty much fit the entire record of fossils that are candidates for the origin of the genus Homo from this time period onto a small table. But, with the discovery of Australopithecus sediba and the wealth of fossils we've recovered—and are recovering—that has changed dramatically," Berger said.

The name itself, "sediba," means "fountain" or "wellspring" in the seSotho language, spoken in South Africa, and indeed, researchers do believe that the new fossils will provide a wealth of information about our human origins.

For now, these new hominid fossils make it clear that the evolutionary transition from small-bodied, and perhaps more tree-dwelling, ancestors to larger-bodied, full-striding bipeds occurred in gradual steps.

Berger, from the University of Witwatersrand in South Africa, along with Paul Dirks from James Cook University in Australia began a study on the distribution of cave deposits in the Cradle of Humankind—a World Heritage Site, set aside for its physical and cultural significance—in January 2008. Months later, Berger discovered the two partial skeletons in cave deposits at Malapa, South Africa, and analyzed the remains, including most of a skull, pelvis, and ankle of the new species with colleagues from the U.S., Switzerland, and Australia.

The two Australopithecus sediba—an adult female and a juvenile male—were found close together in a portion of the cave system that had been protected from scavengers, so the fossils are very well-preserved. The researchers describe the hominid's physical traits, highlighting the unique pelvic features and small teeth that it shared with early Homo species. Based on its physique, they suggest that the new species descended from Australopithecus africanus, and that the hominid's appearance signified the dawn of more energy-efficient walking and running.

"These fossils give us an extraordinarily detailed look into a new chapter of human evolution, and provide a window into a critical period when hominids made the committed change from dependency on life in the trees to life on the ground," said Berger. "Australopithecus sediba appears to present a mosaic of features demonstrating an animal comfortable in both worlds."

In a separate report published in Science, Paul Dirks and colleagues from around the world analyze the Malapa cave system, date the fossil deposits, and describe the geological and ecological environment that Australopithecus sediba would have dwelled in long ago.

"We think the environment sediba lived in was, in many ways, similar to the environment today," Dirks said. "For example, one with predominantly grassy plains, transected by more vegetated, wooded valleys. However, the rivers flowed in different directions and the landscape was not static, but changed all the time."

The caves at Malapa are not randomly distributed, but occur along fracture zones that criss-cross the landscape. They consist of mostly quartz, chert, dolomite, and peloids—though there are also iron-oxide coated grains, ooids, shale, and feldspar in the rocks.

"The fossils occur together in a near-articulated state in the sedimentary remains of a deeply eroded cave system," Dirks continued. "They were laid down by a single debris flow, indicating the timing of their deaths were closely related and occurred shortly before the debris flow carried them to their place of burial."

The researchers identified the fossils of at least 25 other species of animals, including saber-toothed cats, a wildcat, a brown hyena, a wild dog, antelopes, and a horse in the cave as well. They suggest that the Malapa caves were tens of meters deep when the Australopithecus sediba fossils were deposited—and also propose that the cave dwelling could have acted as a death trap for animals seeking water.

"One possible explanation for their entry into the cave could have been that they needed water," said Dirks. "To explain the fossil assemblage and their well-preserved state, we would speculate that perhaps at the time of their death, the area in which sediba lived experienced a severe drought… Animals may have smelled the water, ventured in too deep, fallen down hidden shafts in the pitch dark, or got lost and died."

New hominid species discovered and described in South Africa


A team led by Professor Lee Berger, a renowned palaeoanthropologist from the University of the Witwatersrand, Johannesburg (aka Wits University) have described and named a new species of hominid, Australopithecus sediba, almost two million years old, which was discovered in the Cradle of Humankind World Heritage Site, 40 kilometres out of Johannesburg, South Africa.

Two papers related to this find, authored by Prof. Lee Berger and Prof. Paul Dirks respectively, will be published in the journal Science on Friday, 9 April 2010.

"Sediba, which means natural spring, fountain or wellspring in Sotho, one of the 11 official languages of South Africa, was deemed an appropriate name for a species that might be the point from which the genus Homo arises," comments Berger. "I believe that this is a good candidate for being the transitional species between the southern African ape-man Australopithecus africanus (like the Taung Child and Mrs. Ples) and either Homo habilis or even a direct ancestor of Homo erectus (like Turkana Boy, Java man or Peking man)."

The fossils, a juvenile male and an adult female, were deposited within a single debris flow and occur together in a near articulated state in the remains of a deeply eroded cave system. The sedimentary and geological context indicates that the timing of their death was closely related and occurred shortly before the debris flow carried them to their place of burial.

The species has long arms, like an ape, short powerful hands, a very advanced pelvis (hip bone) and long legs capable of striding and possibly running like a human. It is likely that they could have climbed. "It is estimated that they were both about 1.27 metres, although the child would certainly have grown taller. The female probably weighed about 33 kilograms and the child about 27 kilograms at the time of his death," adds Prof. Berger. "The brain size of the juvenile was between 420 and 450 cubic centimetres, which is small (when compared to the human brain of about 1200 to 1600 cubic centimetres) but the shape of the brain seems to be more advanced than that of australopithecines."

Through a combination of faunal, U-Pb and palaeomagnetic dating techniques, the age of the rocks encasing the fossils has been determined at 1.95-1.78 Ma. . Cosmogenic dating was used to interpret the landscape formation and to determine the depth of the cave at the time.

The skeletons were found amongst the articulated skeletons of a sabre-toothed cat, antelope, mice and rabbits. They are preserved in a hard, concrete like substance known as calcified clastic sediment that formed at the bottom of what appears to be a shallow underground lake or pool that was possibly about 50 metres tall about 1,9 million years ago.

Fossil preparators have worked arduously over the last two years to extract the bones from the rock. About 60 leading scientists from around the world and tens of students have had the opportunity to work on these amazing fossils. The most sophisticated scanning technology has been used to unveil the secrets of the past.

The site continues to be explored and without a doubt there are more groundbreaking discoveries to come forth. In celebration of this find, the children of South Africa have been invited to develop a common name for the juvenile skeleton. The fossils are owned by the people of South Africa, and curated by the University of the Witwatersrand, Johannesburg.


What does Australopithecus sediba mean?
Australopithecus means "southern ape", after the genus of the Taung child, named by Prof. Raymond Dart, also from the University of the Witwatersrand, Johannesburg. Sediba means natural spring, fountain or wellspring in Sotho, an appropriate name for a species that might be the point from which the genus Homo arises.

What is a hominid/hominin?
A hominid is a member of the taxonomic family that includes humans, chimpanzees, gorillas and their extinct ancestors. Hominins are members of the human branch after the human lineage split from that of chimpanzees, and thus include living humans and extinct human ancestors, such as the Australopiths. Hominins are characterised by bipedal locomotion, although this may not have been the case for the very earliest members of the group, and relatively small canine teeth. Later members of this group (those in the genus, Homo) are characterised by larger brains than those of living apes like chimpanzees, bonobos, gorillas, orangutans and gibbons.

How were the fossils dated?
They were dated using a variety of methods including Uranium-Lead, palaeomagnetic and faunal dating systems. Cosmogenic dating was used to interpret the landscape formation and to determine the depth of the cave at the time.

How were the individuals preserved?
The site where the fossils were discovered is technically the infill of a de-roofed cave that was about 50 metres underground 1.9 million years ago. The individuals appear to have fallen, along with other animals, into a deep cave, landing up on the floor for a few days or weeks. The bodies were then washed into an underground lake or pool probably pushed there by a large rainstorm. They did not travel far, maybe a few metres, where they were solidified, as if thrown into quick setting concrete. The rock they are preserved in is called calcified clastic sediment. Over the past 1.9 million years the land has eroded to expose the fossil bearing sediments.

Did they die at the same time, or was it a catastrophe?
The hominin skeletons were found with the bones either in partial articulation or in close anatomical association, which suggests that both bodies were only partially decomposed at the time of deposition in the lower chamber. This further suggests that they died very close in time to each other, either at the same time, or hours, days or weeks apart.

How old is the child?
The juvenile is around 10 – 13 years old in human developmental terms. He was probably a bit younger in actual age (perhaps as young as eight or nine or so) as he is likely to have matured faster than humans. The age estimate is based on modern human standards by which the eruption stages of the teeth are evaluated and the degree of development of the growth centres of the bones.

How old is the female skeleton?
Based on the extreme wear of her teeth, she is probably at least in her late twenties or early thirties.

Did she have children?
It is likely that a female Australopith of her age would have had children.

How do you know the child is a male?
There are features of the face that help us determine that the child is a male. The muscles of the child are larger than that of the other skeleton, even though it is a child. There are also features of the pelvis that we can use to determine that it is a male.

How does this find relate to Lucy?
Australopithecus sediba is approximately a million years younger than Lucy. Some scientists feel that Lucy's species, Au. Afarensis, gave rise to Au. africanus and Lee et al are suggesting that Au. africanus or something similar, gave rise to Au. Sediba.

How do you know that it is a new species?
The team compared the skeletons with all the remains of fossil hominids that have been discovered and in many ways they are absolutely unique from any fossil species found.

Why is this not the genus Homo?
The fossils have an overall body plan that is like that of other Australopiths – they have small brains, relatively small bodies and long and seemingly powerful arms. They do have some features in the skull and pelvis that are found in members of the genus Homo but not in other Australopiths. However, given the small brains and Australopith-like upper body, the team felt that keeping this species in the genus Australopithecus was the conservative thing to do.

What about Homo habilis?
Our study indicates that Australopithecus sediba may be a better ancestor of Homo erectus and it may certainly help to clear up some of this "muddle in the middle".

Why is there still rock attached to the child's skull?
Due to the fragility of the base of the cranium of the specimen and to preserve part of the adhering matrix for future research, the team has decided to leave the specimen partially in rock. The team has been able to visualise this hidden part using scanning technology.

Ancient Assyrian Treaty Discovered

A cache of cuneiform tablets unearthed by a team led by a University of Toronto archaeologist has been found to contain a largely intact Assyrian treaty from the early 7th century BCE.

"The tablet is quite spectacular. It records a treaty — or covenant — between Esarhaddon, King of the Assyrian Empire and a secondary ruler who acknowledged Assyrian power. The treaty was confirmed in 672 BCE at elaborate ceremonies held in the Assyrian royal city of Nimrud (ancient Kalhu). In the text, the ruler vows to recognize the authority of Esarhaddon's successor, his son Ashurbanipal," said Timothy Harrison, professor of near eastern archaeology in the Department of Near & Middle Eastern Civilizations and director of U of T's Tayinat Archaeological Project (TAP).

"The treaties were designed to secure Ashurbanipal's accession to the throne and avoid the political crisis that transpired at the start of his father's reign. Esarhaddon came to power when his brothers assassinated their father, Sennacherib."

The 43 by 28 centimetre tablet — known as the Vassal Treaties of Esarhaddon — contains about 650 lines and is in a very fragile state. "It will take months of further work before the document will be fully legible," added Harrison. "These tablets are like a very complex puzzle, involving hundreds of pieces, some missing. It is not just a matter of pulling the tablet out, sitting down and reading. We expect to learn much more as we restore and analyze the document."

The researchers hope to glean information about Assyria's imperial relations with the west during a critical period, the early 7th century BCE. It marked the rise of the Phrygians and other rival powers in highland Anatolia — now modern-day Turkey — along the northwestern frontier of the Assyrian empire, and coincided with the divided monarchy of Biblical Israel, as well as an era of increased contact between the Levantine peoples of the Eastern Mediterranean and Egypt, as well as the Greeks of the Aegean world.

The cache of tablets — which date back to the Iron Age — were unearthed in August 2009 during excavations at the site of an ancient temple at Tell Tayinat, located in southeastern Turkey. A wealth of religious paraphernalia — including gold, bronze and iron implements, libation vessels and ornately decorated ritual objects — was also uncovered.

Tuesday, April 6, 2010

Archaeologists uncover land before wheel; site untouched for 6,000 years

Previously unexcavated site reveals clues about world's first cities

A team of archaeologists from the University of Chicago's Oriental Institute, along with a team of Syrian colleagues, is uncovering new clues about a prehistoric society that formed the foundation of urban life in the Middle East prior to invention of the wheel.

The mound of Tell Zeidan in the Euphrates River Valley near Raqqa, Syria, which had not been built upon or excavated for 6,000 years, is revealing a society rich in trade, copper metallurgy and pottery production. Artifacts recently found there are providing more support for the view that Tell Zeidan was among the first societies in the Middle East to develop social classes according to power and wealth.

Tell Zeidan dates from between 6000 and 4000 B.C., and immediately preceded the world's first urban civilizations in the ancient Middle East. It is one of the largest sites of the Ubaid culture in northern Mesopotamia.

Thus far, archaeologists have unearthed evidence of this society's trade in obsidian and production and development of copper processing, as well as the existence of a social elite that used stone seals to mark ownership of goods and culturally significant items.

"The project addresses questions not only of how such societies emerged but how they were sustained and flourished," said John Yellen, program director for archaeology in the National Science Foundation's (NSF) Social, Behavioral & Economic Sciences directorate. NSF supports the University of Chicago's research.

Covering about 31 acres, Tell Zeidan was situated where the Balikh River joins the Euphrates River in modern-day Syria. The location was at the crossroads of major, ancient trade routes in Mesopotamia that followed the course of the Euphrates River valley. The Ubaid period lasted from about 5300 to 4000 B.C.

"This enigmatic period saw the first development of widespread irrigation, agriculture, centralized temples, powerful political leaders and the first emergence of social inequality as communities became divided into wealthy elites and poorer commoners," said Gil Stein, director of the Oriental Institute and a leader of the expedition.

"The research also is important because it provides insight into how complex societies, based on linkages which extended across hundreds of miles, developed," said Yellen, noting the distance travelled for raw materials needed for many of the Tell Zeidan artifacts.

For example, copper ore was carried by workers from sources near modern-day Diyarbakir, Turkey, about 185 to 250 miles away, then smelted at Tell Zeidan to produce metal tools and other implements.

One of the most remarkable finds was a stone stamp seal depicting a deer, Stein said. The seal was about two inches by two-and-a-half inches and was carved from a red stone not native to the area. A similar seal design was found 185 miles to the east near Mosul in northern Iraq.

"The existence of very elaborate seals with near-identical motifs at such widely distant sites suggests that in this period, high-ranking elites were assuming leadership positions across a very broad region, and those dispersed elites shared a common set of symbols and perhaps even a common ideology of superior social status," said Stein.

Stein said Tell Zeidan may have been one of the largest Ubaid temple towns in northern Mesopotamia, and that it was as large or larger than any previously known contemporary Ubaid towns in the southern alluvial lowlands of the Tigris and Euphrates rivers in what is today southern Iraq. However, because the site was not occupied after about 4,000 B.C., the prehistoric strata of Tell Zeidan are immediately accessible beneath the modern-day ground surface instead of being buried beneath layers of deposits from later periods.

"This means that, for the first time, archaeologists can excavate broad areas of an Ubaid temple town to understand how a proto-urban community actually functioned in the sixth-fifth millennia B.C.," Stein said.

The new excavations Tell Zeidan reveal the emergence of an elite that possessed the political power necessary for communities to move from self-sufficient village life to societies dependent on trade and capable of acquiring luxury goods, Stein said.

"The two-millennium-long occupation spans four key periods: two phases of the late Copper Age on top, the Ubaid period in the middle and the Halaf period at the bottom," Stein said.

The excavations so far show that the transitions between these periods were peaceful, including the period in which the influence of the Ubaid culture spread from its south Mesopotamian homeland up the Euphrates River into north Syria.

The team found obsidian blades and chips wasted during the production of the blades. The high-quality volcanic glass had to be brought to the community from sources 250 miles away in what is now Turkey. The greenish-black color and chemical composition show that it came from mines in the eastern part of the country.

The people in Tell Zeidan also had access to copper ore from sources near modern-day Diyarbakir, Turkey, about 185 to 250 miles away. Those materials were smelted at Tell Zeidan to produce metal tools that represent the most advanced technology of the fifth millennium B.C. People must have transported the material on their backs, however, as Tell Zeidan flourished at a time before donkeys were domesticated.

The wealth of the community came from irrigation-based agriculture, trade and manufacturing. "We found flint sickle blades everywhere, easily recognizable from the glossy sheen where they had been polished by the silica in the stems of the wheat that they were used to harvest," Stein said. The people used bitumen, a tar substance obtained from pits 43 miles away, to secure the blades onto handles.

Along with the advanced technology, a wealthy ruling class and individual identification by stamp seals, the people at Tell Zeidan also built large public structures of mud bricks.
Stein said the location's potential for further discoveries is so great the project is likely to last for decades.