People always seem to be digging up stuff from below the ground - artifacts, buildings and entire cities. Often they are below a current city.
My question is - where do the layers covering the stuff keep coming from? Once upon a time the city was at the ground level and people were walling the streets, and now it is buried underground. Did the ground sink slowly? How did the old stuff get covered by new stuff? Where did the new stuff come from, considering it would take a lot of material to cover an entire city!
How come these ruins are never seem to be at the top? Has anyone done a study of this?
29,000 Years of Aboriginal History: Uncovering New Layers of River Murray Occupation
The known timeline of the Aboriginal occupation of South Australia’s Riverland region has been vastly extended by new research led by Flinders University in collaboration with the River Murray and Mallee Aboriginal Corporation (RMMAC).
Radiocarbon dating of shell middens — remnants of meals eaten long ago — capture a record of Aboriginal occupation that extends to around 29,000 years, confirming the location as one of the oldest sites along the 2500km river to become the oldest River Murray Indigenous site in South Australia.
Location map shows the areas studied by archaeologists and the River Murray and Mallee Aboriginal community in South Australia. Credit: Flinders University
In the first comprehensive survey of the region, one of the oldest Indigenous sites along Australia’s longest river system has been discovered. The results, published in Australian Archaeology, used radiocarbon dating methods to analyze river mussel shells from a midden site overlooking the Pike River floodplain downstream of Renmark.
“These results include the first pre-Last Glacial Maximum ages returned on the River Murray in South Australia and extend the known Aboriginal occupation of the Riverland by approximately 22,000 years,” says Flinders University archaeologist and PhD candidate Craig Westell.
More than 30 additional radiocarbon dates were collected in the region, spanning the period from 15,000 years ago to the recent present. Together, the results relate Aboriginal people to an ever-changing river landscape, and provide deeper insights into how they responded to these challenges.
The period represented by the radiocarbon results brackets the Last Glacial Maximum (commonly known as the last Ice Age) when climatic conditions were colder and drier and when the arid zone extended over much of the Murray-Darling Basin. The river and lake systems of the basin were under stress during this time.
In the Riverland, dunes were advancing into the Murray floodplains, river flows were unpredictable, and salt was accumulating in the valley.
Timothy Johnson (River Murray and Mallee Aboriginal Corporation), left, and Craig Westall recording a hearth feature at Calperum Station. Credit: Flinders University
The ecological impacts witnessed during one of the worst droughts on record, the so-called Millennium Drought (from late 1996 extending to mid-2010), provides an idea of the challenges Aboriginal people may have faced along the river during the Last Glacial Maximum, and other periods of climate stress, researchers conclude.
“These studies show how our ancestors have lived over many thousands of years in the Riverland region and how they managed to survive during times of hardship and plenty,” says RMMAC spokesperson Fiona Giles.
“This new research, published in Australian Archaeology, fills in a significant geographic gap in our understanding of the Aboriginal occupation chronologies for the Murray-Darling Basin,” adds co-author Associate Professor Amy Roberts.
The dating, which was undertaken at the Australian Nuclear Science and Technology Organisation (ANSTO) and Waikato University, forms part of a much larger and ongoing research program led by Associate Professor Amy Roberts which is undertaking a broad-ranging investigation of past and contemporary Aboriginal connections to the Riverland region.
Reference: “Initial results and observations on a radiocarbon dating program in the Riverland region of South Australia” by C Westell, A Roberts, M Morrison, G Jacobsen and the River Murray and Mallee Aboriginal Corporation, 14 July 2020, Australian Archaeology.
The Last Glacial Maximum is the most significant climatic event to face modern humans since their arrival in Australia some 40,000-50,000 years ago. Recent studies have demonstrated that the LGM in Australia was a period of significant cooling and increased aridity beginning ?30 ka and peaking between ?23 and 18 ka.
Historical Research Techniques
Archival research is often the first step in archaeology. This research uncovers the written records associated with the study area. If people lived in the area when there were written records, the archaeologist will look for associated primary historical documents. This archival research may take the archaeologist to public or university libraries, the local historical society or courthouse—or even into people’s homes! Primary documents could include: maps and/or photographs of the area, newspapers, land and tax records, and diaries or letters.
In addition to primary historical documents, archaeologists will look for site reports that other archaeologists have written about this area. These reports will describe what the archaeologist found in this area during any previous investigations. These older site reports can help guide the new research. The State Historic Preservation Office maintains documentation files for all the recorded archaeological sites in each state. This will include previous archaeological research reports about sites in the state.
Oral history is another research method that archaeologists and historians may use to gather information. It includes information passed down by word of mouth. Stories passed down about your family history and traditions that your family observes are oral history.
Archaeologists today collaborate with descendants to better understand the cultural traditions of their pasts. Archaeologists working on the 19th-century Levi Jordan Plantation in Texas interviewed descendants. They included both descendants of the plantation owners and of the enslaved plantation workers as part of their research. These archaeologists wanted to include the voices and perspectives of all the past peoples who lived and worked there. At Castle Rock Pueblo in southwestern Colorado, archaeologists used oral history. Through the oral traditions of modern Puebloan people, they learned about the past culture of their Anasazi ancestors.
Why This Archaeology Activity is Relevant
This activity gives us a visual of how stratigraphy works. Each layer of salt is a different colour, just as the different layers of sub-soil and top-soil are different colours depending on location and what created them. At the very bottom of our site, we have our oldest item – the shell or fossil. Next, we have some broken pottery representing a past human layer. Finally, at the top, we have the metal pop tab, a ‘new artifact’ of the present time.
This cookie excavation will help children understand the care that must be taken while excavating in order to not damage the fragile artifacts (in this case the chocolate chips). They will also appreciate how they have destroyed the cookie (archaeological site) in the process. However, by recording all their artifacts the information of their cookie will survive.
- Give each child a cookie, activity sheet, and two toothpicks.
- Before starting the excavation, children should place their cookie on Grid A. Then draw the cookie, with all the visible artifacts (chocolate chips) included. This will be their record of the archaeological site.
- Excavate cookies with the toothpicks, by carefully chipping away at the dirt (cookie) to slowly reveal any hidden artifacts. For an added challenge, remind them that they should not pick up their cookies because archaeologists cannot pick up sites!
- For each “artifact” found add it to the drawing on grid B.
- At the end each child should have a pile of back dirt (cookie crumbs) and artifacts (chocolate chips), and their drawing of what they looked like before.
- Count artifacts who has excavated the most?
- Eat the destroyed cookie!
Why is this Relevant?
Archaeological excavations are a destructive process. When archaeologists have finished with a site, they have largely taken it apart piece by piece to discover its secrets. Unfortunately, this means a site, once excavated, can’t be excavated again. To fix this problem, archaeologists take lots of notes, drawings, photographs, take samples of soils, and write detailed reports so archaeologists in the future can come back to their excavations and learn even more. Without all these notes and reports all the context we learned about in the stratigraphy activity above will be lost forever.
We hope you enjoy this archaeology activities with your adventurer.
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The city, said to have been planned by Ur-Nammu, was apparently divided into neighbourhoods, with merchants living in one quarter, artisans in another. There were streets both wide and narrow, and open spaces for gatherings. Many structures for water resource management and flood control are in evidence. 
Houses were constructed from mudbricks and mud plaster. In major buildings, the masonry was strengthened with bitumen and reeds. For the most part, foundations are all that remain today. People were often buried (separately and alone sometimes with jewellery, pots, and weapons) in chambers or shafts beneath the house floors. 
Ur was surrounded by sloping ramparts 8 metres high and about 25 metres wide, bordered in some places by a brick wall. Elsewhere, buildings were integrated into the ramparts. The Euphrates River complemented these fortifications on the city's western side. 
Archaeological discoveries have shown unequivocally that Ur was a major Sumero-Akkadian urban center on the Mesopotamian plain. Especially the discovery of the Royal Tombs has confirmed its splendour. These tombs, which date to the Early Dynastic IIIa period (approximately in the 25th or 24th century BC), contained an immense treasure of luxury items made of precious metals and semi-precious stones imported from long distances (Ancient Iran, Afghanistan, India, Asia Minor, the Levant and the Persian Gulf).  This wealth, unparalleled up to then, is a testimony of Ur's economic importance during the Early Bronze Age. 
Archaeological study of the region has contributed greatly to our understanding of the landscape and long-distance interactions during these ancient times. Ur was a major port on the Persian Gulf, which extended much further inland than today, and the city controlled much of the trade into Mesopotamia. Imports to Ur came from many parts of the world: precious metals such as gold and silver, and semi-precious stones, namely lapis lazuli and carnelian. 
It is thought that Ur had a stratified social system including slaves (captured foreigners), farmers, artisans, doctors, scribes, and priests. High-ranking priests apparently enjoyed great luxury and splendid mansions. 
Tens of thousands of cuneiform texts have been recovered from temples, the palace, and individual houses, recording contracts, inventories, and court documents, evidence of the city's complex economic and legal systems. 
Excavation in the old city of Ur in 1929 revealed lyres, instruments similar to the modern harp but in the shape of a bull and with eleven strings. 
When Ur was founded, the Persian Gulf's water level was two-and-a-half metres higher than today. Ur is therefore thought to have had marshy surroundings irrigation would have been unnecessary, and the city's evident canal system was likely used for transportation. Fish, birds, tubers, and reeds might have supported Ur economically without the need for an agricultural revolution sometimes hypothesized as a prerequisite to urbanization.  
Archaeologists have discovered the evidence of an early occupation at Ur during the Ubaid period (ca. 6500 to 3800 BC). These early levels were sealed off with a sterile deposit of soil that was interpreted by excavators of the 1920s as evidence for the Great Flood of the Book of Genesis and Epic of Gilgamesh. It is now understood that the South Mesopotamian plain was exposed to regular floods from the Euphrates and the Tigris rivers, with heavy erosion from water and wind, which may have given rise to the Mesopotamian and derivative Biblical Great Flood stories.  
Sumerian occupation of the 4th millennium Edit
The further occupation of Ur only becomes clear during its emergence in the third millennium BC (although it must already have been a growing urban center during the fourth millennium). As other Sumerians, the new settlers of Ur were a non-Semitic people who may have come from the east circa 3300 BCE, and spoke a language isolate.   But during the 3rd millennium BC, a close cultural symbiosis developed between the Sumerians and the East-Semitic Akkadians,  which gave rise to widespread bilingualism.  The reciprocal influence of the Sumerian language and the Akkadian language is evident in all areas, from pervasive lexical borrowing, to syntactic, morphological, and phonological convergence.  This has prompted scholars to refer to Sumerian and Akkadian in the 3rd millennium BC as a Sprachbund. 
The third millennium BC is generally described as the Early Bronze Age of Mesopotamia, which ends approximately after the demise of the Third Dynasty of Ur in the 21st century BC.
Third millennium BC (Early Bronze Age) Edit
There are various main sources informing scholars about the importance of Ur during the Early Bronze Age. The First Dynasty of Ur seems to have had great wealth and power, as shown by the lavish remains of the Royal Cemetery at Ur. The Sumerian King List provides a tentative political history of ancient Sumer and mentions, among others, several rulers of Ur. Mesannepada is the first king mentioned in the Sumerian King List, and appears to have lived in the 26th century BC. That Ur was an important urban centre already then seems to be indicated by a type of cylinder seal called the City Seals. These seals contain a set of proto-cuneiform signs which appear to be writings or symbols of the name of city-states in ancient Mesopotamia. Many of these seals have been found in Ur, and the name of Ur is prominent on them. 
A large body of cuneiform documents, mostly from the empire of the so-called Third Dynasty of Ur (also known as the Neo-Sumerian Empire), appears at the very end of the third millennium. This was the most centralized bureaucratic state the world had yet known.
Ur came under the control of the Semitic-speaking Akkadian Empire founded by Sargon the Great between the 24th and 22nd centuries BC. This was a period when the Semitic-speaking Akkadians, who had entered Mesopotamia in approximately 3000 BC, gained ascendancy over the Sumerians, and indeed much of the ancient Near East.
After the fall of the Akkadian Empire in the mid-22nd century BC, southern Mesopotamia came to be ruled for a few decades by the Gutians, a language isolate-speaking barbarian people originating in the Zagros Mountains to the northeast of Mesopotamia, while the Assyrian branch of the Akkadian speakers reasserted their independence in the north of Mesopotamia.
Ur III Edit
The third dynasty was established when the king Ur-Nammu came to power, ruling between ca. 2047 BC and 2030 BC. During his rule, temples, including the Ziggurat of Ur, were built, and agriculture was improved through irrigation. His code of laws, the Code of Ur-Nammu (a fragment was identified in Istanbul in 1952) is one of the oldest such documents known, preceding the Code of Hammurabi by 300 years. He and his successor Shulgi were both deified during their reigns, and after his death he continued as a hero-figure: one of the surviving works of Sumerian literature describes the death of Ur-Nammu and his journey to the underworld. 
Ur-Nammu was succeeded by Shulgi, the greatest king of the Third Dynasty of Ur, who solidified the hegemony of Ur and reformed the empire into a highly centralized bureaucratic state. Shulgi ruled for a long time (at least 42 years) and deified himself halfway through his rule. 
The Ur empire continued through the reigns of three more kings with Semitic Akkadian names,  Amar-Sin, Shu-Sin, and Ibbi-Sin. It fell around 1940 BC to the Elamites in the 24th regnal year of Ibbi-Sin, an event commemorated by the Lament for Ur.  
According to one estimate, Ur was the largest city in the world from c. 2030 to 1980 BC. Its population was approximately 65,000 (or 0.1 per cent share of global population then). 
Later Bronze Age Edit
The city of Ur lost its political power after the demise of the Third Dynasty of Ur. Nevertheless, its important position which kept on providing access to the Persian Gulf ensured the ongoing economic importance of the city during the second millennium BC. The splendour of the city, the might of the empire, the greatness of king Shulgi, and undoubtedly the efficient propaganda of the state endured throughout Mesopotamian history. Shulgi was a well known historical figure for at least another two thousand years, while historical narratives of the Mesopotamian societies of Assyria and Babylonia kept names, events, and mythologies in remembrance. The city came to be ruled by the first dynasty (Amorite) of Babylonia which rose to prominence in southern Mesopotamia in the 18th century BC. After the fall of Hammurabi's short lived Babylonian Empire, it later became a part of the native Akkadian ruled Sealand Dynasty for over 270 years, and was reconquered into Babylonia by the successors of the Amorites, the Kassites in the 16th century BC. During the Kassite Dynastic period Ur, along with the rest of Babylonia, came under sporadic control of the Elamites and the Middle Assyrian Empire, the latter of which straddled the Late Bronze Age and Early Iron Age periods between the early 14th century BC and mid 11th century BC.
Iron Age Edit
The city, along with the rest of southern Mesopotamia and much of the Near East, Asia Minor, North Africa and southern Caucasus, fell to the north Mesopotamian Neo-Assyrian Empire from the 10th to late 7th centuries BC.
From the end of the 7th century BC Ur was ruled by the so-called Chaldean Dynasty of Babylon. In the 6th century BC there was new construction in Ur under the rule of Nebuchadnezzar II of Babylon. The last Babylonian king, Nabonidus (who was Assyrian-born and not a Chaldean), improved the ziggurat. However, the city started to decline from around 530 BC after Babylonia fell to the Persian Achaemenid Empire, and was no longer inhabited by the early 5th century BC.  The demise of Ur was perhaps owing to drought, changing river patterns, and the silting of the outlet to the Persian Gulf.
Ur is possibly the city of Ur Kasdim mentioned in the Book of Genesis as the birthplace of the Jewish, Christian and Muslim patriarch Abraham (Ibrahim in Arabic), traditionally believed to have lived some time in the 2nd millennium BC.    There are however conflicting traditions and scholarly opinions identifying Ur Kasdim with the sites of Şanlıurfa, Urkesh, Urartu or Kutha.
The biblical Ur is mentioned four times in the Torah or Old Testament, with the distinction "of the Kasdim/Kasdin"—traditionally rendered in English as "Ur of the Chaldees". The Chaldeans had settled in the vicinity by around 850 BC, but were not extant anywhere in Mesopotamia during the 2nd millennium BC period when Abraham is traditionally held to have lived. The Chaldean dynasty did not rule Babylonia (and thus become the rulers of Ur) until the late 7th century BC, and held power only until the mid 6th century BC. The name is found in Genesis 11:28, Genesis 11:31, and Genesis 15:7. In Nehemiah 9:7, a single passage mentioning Ur is a paraphrase of Genesis.
In 1625, the site was visited by Pietro Della Valle, who recorded the presence of ancient bricks stamped with strange symbols, cemented together with bitumen, as well as inscribed pieces of black marble that appeared to be seals.
European archaeologists did not identify Tell el-Muqayyar as the site of Ur until Henry Rawlinson successfully deciphered some bricks from that location, brought to England by William Loftus in 1849. 
The site was first excavated in 1853 and 1854, on behalf of the British Museum and with instructions from the Foreign Office, by John George Taylor, British vice consul at Basra from 1851 to 1859.    Taylor uncovered the Ziggurat of Ur and a structure with an arch later identified as part of the "Gate of Judgment". 
In the four corners of the ziggurat's top stage, Taylor found clay cylinders bearing an inscription of Nabonidus (Nabuna`id), the last king of Babylon (539 BC), closing with a prayer for his son Belshar-uzur (Bel-ŝarra-Uzur), the Belshazzar of the Book of Daniel.  Evidence was found of prior restorations of the ziggurat by Ishme-Dagan of Isin and Shu-Sin of Ur, and by Kurigalzu, a Kassite king of Babylon in the 14th century BC. Nebuchadnezzar also claims to have rebuilt the temple. 
Taylor further excavated an interesting Babylonian building, not far from the temple, part of an ancient Babylonian necropolis.  All about the city he found abundant remains of burials of later periods.  Apparently, in later times, owing to its sanctity, Ur became a favorite place of sepulchres, so that even after it had ceased to be inhabited, it continued to be used as a necropolis. 
Typical of the era, his excavations destroyed information and exposed the tell. Natives used the now loosened, 4,000-year-old bricks and tile for construction for the next 75 years, while the site lay unexplored,  the British Museum having decided to prioritize archaeology in Assyria. 
After Taylor's time, the site was visited by numerous travelers, almost all of whom have found ancient Babylonian remains, inscribed stones and the like, lying upon the surface.  The site was considered rich in remains, and relatively easy to explore. After some soundings were made in 1918 by Reginald Campbell Thompson, H. R. Hall worked the site for one season for the British Museum in 1919, laying the groundwork for more extensive efforts to follow.  
Excavations from 1922 to 1934 were funded by the British Museum and the University of Pennsylvania and led by the archaeologist Sir Charles Leonard Woolley.    A total of about 1,850 burials were uncovered, including 16 that were described as "royal tombs" containing many valuable artifacts, including the Standard of Ur. Most of the royal tombs were dated to about 2600 BC. The finds included the unlooted tomb of a queen thought to be Queen Puabi  —the name is known from a cylinder seal found in the tomb, although there were two other different and unnamed seals found in the tomb. Many other people had been buried with her, in a form of human sacrifice. Near the ziggurat were uncovered the temple E-nun-mah and buildings E-dub-lal-mah (built for a king), E-gi-par (residence of the high priestess) and E-hur-sag (a temple building). Outside the temple area, many houses used in everyday life were found. Excavations were also made below the royal tombs layer: a 3.5-metre-thick (11 ft) layer of alluvial clay covered the remains of earlier habitation, including pottery from the Ubaid period, the first stage of settlement in southern Mesopotamia. Woolley later wrote many articles and books about the discoveries.  One of Woolley's assistants on the site was the archaeologist Max Mallowan. The discoveries at the site reached the headlines in mainstream media in the world with the discoveries of the Royal Tombs. As a result, the ruins of the ancient city attracted many visitors. One of these visitors was the already famous Agatha Christie, who as a result of this visit ended up marrying Max Mallowan.
During this time the site was accessible from the Baghdad–Basra railway, from a stop called "Ur Junction". 
When the Royal Tombs at Ur were first discovered, they had no idea how big they were. They started by digging two trenches in the middle of the desert to see if they could find anything that would allow them to keep digging. They originally split into two teams. Team A and team B. Both teams spent the first few months digging a trench and had found evidence of burial grounds by collecting small pieces of golden jewelry and pottery. This was called at the time the "gold trench"  At this time, the first season of digging had come to a close, and Woolley returned to England. In Autumn, Woolley returned and continued to dig into the second season. By the end of the second season, he had uncovered a courtyard  surrounded by many rooms.  In their third season of digging they had uncovered their biggest find yet, a building that was believed to have been built by the orders of the king, and the second building to be where the high priestess lived. As the fourth and fifth season came to a close, they had discovered so many items, that most of their time was now spent recording the objects they found instead of actually digging objects. They had found many items from gold jewelry to clay pots and stones. There were a few Lyres that were inside of the tombs as well. One of the most significant objects that was discovered was the Standard of Ur. At the end of their sixth season they had excavated 1850 burials and deemed 17 of them to be "Royal Tombs".  Woolley had finished his work excavating the Royal Tombs of UR in 1934. Woolley uncovered a series of burials. He referred to these findings as the "Royal tombs" and the "Death Pit." Many servants were killed and buried with the royals, he believed that these servants went to their deaths willingly. He and his wife and collogue Katherine theorized that these servants were given poisonous drinks and these deaths were a mass suicide as a tribute to their rulers. However computerized tomography scans on some of the surviving skulls have showed signs that they were killed by blows to the head that could be from the spiked end of a copper axe. This evidence proved Woolley's theory of mass suicide via poison incorrect.  Inside princess Puabi's tomb, there was a chest in the middle of the room. Underneath that chest was a hole in the ground that led to what was called the "King's grave" PG-789. It was believed to be the kings grave because it was buried next to the queen. In the "King's Grave" were 63 attendants who were all equipped with copper helmets and swords. It is thought to be his army buried with him. Another large room was uncovered, PG-1237, called the "Great death pit".  This large room had 74 bodies, 68 of which were women. There were only two artifacts in the tomb, both of which were Lyres.
Most of the treasures excavated at Ur are in the British Museum and the University of Pennsylvania Museum of Archaeology and Anthropology. At the Penn Museum the exhibition "Iraq's Ancient Past",  which includes many of the most famous pieces from the Royal Tombs, opened to visitors in late Spring 2011. Previously, the Penn Museum had sent many of its best pieces from Ur on tour in an exhibition called "Treasures From the Royal Tombs of Ur." It traveled to eight American museums, including those in Cleveland, Washington and Dallas, ending the tour at the Detroit Institute of Art in May 2011.
In 2009, an agreement was reached for a joint University of Pennsylvania and Iraqi team to resume archaeological work at the site of Ur. 
Archaeological remains Edit
Though some of the areas that were cleared during modern excavations have sanded over again, the Great Ziggurat is fully cleared and stands as the best-preserved and most visible landmark at the site.  The famous Royal tombs, also called the Neo-Sumerian Mausolea, located about 250 metres (820 ft) south-east of the Great Ziggurat in the corner of the wall that surrounds the city, are nearly totally cleared. Parts of the tomb area appear to be in need of structural consolidation or stabilization.
There are cuneiform (Sumerian writing) on many walls, some entirely covered in script stamped into the mud-bricks. The text is sometimes difficult to read, but it covers most surfaces. Modern graffiti has also found its way to the graves, usually in the form of names made with coloured pens (sometimes they are carved). The Great Ziggurat itself has far more graffiti, mostly lightly carved into the bricks. The graves are completely empty. A small number of the tombs are accessible. Most of them have been cordoned off. The whole site is covered with pottery debris, to the extent that it is virtually impossible to set foot anywhere without stepping on some. Some have colours and paintings on them. Some of the "mountains" of broken pottery are debris that has been removed from excavations. Pottery debris and human remains form many of the walls of the royal tombs area.
In May 2009, the United States Army returned the Ur site to the Iraqi authorities, who hope to develop it as a tourist destination. 
Since 2009, the non-profit organization Global Heritage Fund (GHF) has been working to protect and preserve Ur against the problems of erosion, neglect, inappropriate restoration, war and conflict. GHF's stated goal for the project is to create an informed and scientifically grounded Master Plan to guide the long-term conservation and management of the site, and to serve as a model for the stewardship of other sites. 
Since 2013, the institution for Development Cooperation of the Italian Ministry of Foreign Affairs DGCS  and the SBAH, the State Board of Antiquities and Heritage of the Iraqi Ministry of Tourism and Antiquities, have started a cooperation project for "The Conservation and Maintenance of Archaeological site of UR". In the framework of this cooperation agreement, the executive plan, with detailed drawings, is in progress for the maintenance of the Dublamah Temple (design concluded, works starting), the Royal Tombs—Mausolea 3rd Dynasty (in progress)—and the Ziqqurat (in progress). The first updated survey in 2013 has produced a new aerial map derived by the flight of a UAV (unmanned aerial vehicle) operated in March 2014. This is the first high-resolution map, derived from more than 100 aerial photograms, with an accuracy of 20 cm or less. A preview of the ORTHO-PHOTOMAP of Archaeological Site of UR is available online. 
Tal Abu Tbeirah Edit
Since 2012, a joint team of Italian and Iraqi archaeologists led by Franco D'Agostino have been excavating at Tal Abu Tbeirah, located 15 kilometers east of Ur and 7 kilometers south of Nasariyah.     The site, about 45 hectares in area, appears to have been a harbor and trading center associated with Ur in the later half of the 3rd Millennium BC. 
21 Ways Archaeologists Date Ancient Artifacts
In times past, things that appeared old were simply considered old, maybe as old as the story of Atlantis, the biblical flood or the earth itself, but nobody knew for certain how old anything was. It wasn’t until the late nineteenth century that archaeologists began using dating techniques, specifically those labeled as relative dating, which began to provide an acceptable degree of accuracy for dating old things.
Then in the early twentieth century scientists began using absolute dating techniques, perhaps the most prominent of which is carbon-14. It would be hard to imagine modern archaeology without this elegant and precise dating method. Now using carbon-14 and other modern dating techniques we have a very good idea how old things are.
The following is a list of dating techniques used in archaeology and other sciences. It is written mostly in the order each method was introduced.
Harris matrix used for excavations
Archaeological site of Hisarlik (Troy) in northwesternTurkey
Rock paintings at Chauvet Cave in France
Bedrock milling holes at Sutter Buttes north of Sacramento, California
Pictograph found at Sutter Buttes
Stratigraphy is the most basic and intuitive dating technique and is therefore also the oldest of the relative dating techniques. Based on the law of Superposition, stratigraphy states that lower layers should be older than layers closer to the surface, and in the world of archaeology this is generally the case, unless some natural or manmade event has literally mixed up the layers in some fashion. Most archaeological sites consist of a kind of layer cake of strata, so figuring out how old each layer is comprises the basis for the dating of the site itself and also helps date the artifacts found within these layers as well.
For instance, the site of Hisarlik in western Turkey comprises a manmade earthen mound, also known to archaeologists as a tell, which is covered by of nine layers of strata, the lowest of which appears to be the oldest. Interestingly, Hisarlik could be the site of Homeric Troy (circa 1300 B.C.E.), though this possibility has not been conclusively proven.
2. Seriation or Artifact Sequencing
Invented by preeminent archaeologist Sir William Flinders-Petrie in the late nineteenth century, seriation, another form of relative dating, is based on the idea that over time artifacts such as gravestones and ceramics undergo changes in style, characteristics and use. Seriation is particularly useful when layers of strata are not available, such as at ancient cemeteries.
3. Chronological Markers
The first and simplest method of absolute dating, chronological markers pertain to artifacts with dates inscribed upon them, such as coins, documents or inscriptions on buildings announcing historical events. Roman coins are excellent for this usage, as they often show dates, as well as the likeness of the emperor in power when the coins were minted. The only problem with this dating method is that when these markers are discovered out of context, their value is greatly diminished.
Dendrochronology or tree-ring dating was developed in the early 1900s by Tucson astronomer A. E. Douglass, who hypothesized that the growth rings in trees are influenced by solar flares and sunspot activity. This theory turned out to be true, of course, because solar activity affects virtually every living thing on the planet. These growth rings can be used to date slices of wood or logs, sometimes to the exact calendar year. Douglass’ research led to the dating of Native American puebloan ruins through the American Southwest.
The Greek botanist Theophrastus (c. 371 – c. 287 BC) first mentioned that the wood of trees has rings.   In his Trattato della Pittura (Treatise on Painting), Leonardo da Vinci (1452–1519) was the first person to mention that trees form rings annually and that their thickness is determined by the conditions under which they grew.  In 1737, French investigators Henri-Louis Duhamel du Monceau and Georges-Louis Leclerc de Buffon examined the effect of growing conditions on the shape of tree rings.  They found that in 1709, a severe winter produced a distinctly dark tree ring, which served as a reference for subsequent European naturalists.  In the U.S., Alexander Catlin Twining (1801–1884) suggested in 1833 that patterns among tree rings could be used to synchronize the dendrochronologies of various trees and thereby to reconstruct past climates across entire regions.  The English polymath Charles Babbage proposed using dendrochronology to date the remains of trees in peat bogs or even in geological strata (1835, 1838). 
During the latter half of the nineteenth century, the scientific study of tree rings and the application of dendrochronology began. In 1859, the German-American Jacob Kuechler (1823–1893) used crossdating to examine oaks (Quercus stellata) in order to study the record of climate in western Texas.  In 1866, the German botanist, entomologist, and forester Julius Ratzeburg (1801–1871) observed the effects on tree rings of defoliation caused by insect infestations.  By 1882, this observation was already appearing in forestry textbooks.  In the 1870s, the Dutch astronomer Jacobus C. Kapteyn (1851–1922) was using crossdating to reconstruct the climates of the Netherlands and Germany.  In 1881, the Swiss-Austrian forester Arthur von Seckendorff-Gudent (1845–1886) was using crossdating.  From 1869 to 1901, Robert Hartig (1839–1901), a German professor of forest pathology, wrote a series of papers on the anatomy and ecology of tree rings.  In 1892, the Russian physicist Fedor Nikiforovich Shvedov ( Фёдор Никифорович Шведов 1841–1905) wrote that he had used patterns found in tree rings to predict droughts in 1882 and 1891. 
During the first half of the twentieth century, the astronomer A. E. Douglass founded the Laboratory of Tree-Ring Research at the University of Arizona. Douglass sought to better understand cycles of sunspot activity and reasoned that changes in solar activity would affect climate patterns on earth, which would subsequently be recorded by tree-ring growth patterns (i.e., sunspots → climate → tree rings).
Horizontal cross sections cut through the trunk of a tree can reveal growth rings, also referred to as tree rings or annual rings. Growth rings result from new growth in the vascular cambium, a layer of cells near the bark that botanists classify as a lateral meristem this growth in diameter is known as secondary growth. Visible rings result from the change in growth speed through the seasons of the year thus, critical for the title method, one ring generally marks the passage of one year in the life of the tree. Removal of the bark of the tree in a particular area may cause deformation of the rings as the plant overgrows the scar.
The rings are more visible in trees which have grown in temperate zones, where the seasons differ more markedly. The inner portion of a growth ring forms early in the growing season, when growth is comparatively rapid (hence the wood is less dense) and is known as "early wood" (or "spring wood", or "late-spring wood"  ) the outer portion is the "late wood" (sometimes termed "summer wood", often being produced in the summer, though sometimes in the autumn) and is denser. 
Many trees in temperate zones produce one growth-ring each year, with the newest adjacent to the bark. Hence, for the entire period of a tree's life, a year-by-year record or ring pattern builds up that reflects the age of the tree and the climatic conditions in which the tree grew. Adequate moisture and a long growing season result in a wide ring, while a drought year may result in a very narrow one.
Direct reading of tree ring chronologies is a complex science, for several reasons. First, contrary to the single-ring-per-year paradigm, alternating poor and favorable conditions, such as mid-summer droughts, can result in several rings forming in a given year. In addition, particular tree-species may present "missing rings", and this influences the selection of trees for study of long time-spans. For instance, missing rings are rare in oak and elm trees. 
Critical to the science, trees from the same region tend to develop the same patterns of ring widths for a given period of chronological study. Researchers can compare and match these patterns ring-for-ring with patterns from trees which have grown at the same time in the same geographical zone (and therefore under similar climatic conditions). When one can match these tree-ring patterns across successive trees in the same locale, in overlapping fashion, chronologies can be built up—both for entire geographical regions and for sub-regions. Moreover, wood from ancient structures with known chronologies can be matched to the tree-ring data (a technique called cross-dating), and the age of the wood can thereby be determined precisely. Dendrochronologists originally carried out cross-dating by visual inspection more recently, they have harnessed computers to do the task, applying statistical techniques to assess the matching. To eliminate individual variations in tree-ring growth, dendrochronologists take the smoothed average of the tree-ring widths of multiple tree-samples to build up a ring history, a process termed replication. A tree-ring history whose beginning- and end-dates are not known is called a floating chronology. It can be anchored by cross-matching a section against another chronology (tree-ring history) whose dates are known.
A fully anchored and cross-matched chronology for oak and pine in central Europe extends back 12,460 years,  and an oak chronology goes back 7,429 years in Ireland and 6,939 years in England.  Comparison of radiocarbon and dendrochronological ages supports the consistency of these two independent dendrochronological sequences.  Another fully anchored chronology that extends back 8500 years exists for the bristlecone pine in the Southwest US (White Mountains of California). 
The dendrochronological equation defines the law of growth of tree rings. The equation was proposed by Russian biophysicist Alexandr N. Tetearing in his work "Theory of populations"  in the form:
where ΔL is width of annual ring, t is time (in years), ρ is density of wood, kv is some coefficient, M(t) is function of mass growth of the tree.
Ignoring the natural sinusoidal oscillations in tree mass, the formula for the changes in the annual ring width is:
where c1, c2, and c4 are some coefficients, a1 and a2 are positive constants.
The formula is useful for correct approximation of samples data before data normalization procedure.
The typical forms of the function ΔL(t) of annual growth of wood ring are shown in the figures.
Dendrochronology makes available specimens of once-living material accurately dated to a specific year.  Dates are often represented as estimated calendar years B.P., for before present, where "present" refers to 1 January 1950. 
Timber core samples are sampled and used to measure the width of annual growth rings by taking samples from different sites within a particular region, researchers can build a comprehensive historical sequence. The techniques of dendrochronology are more consistent in areas where trees grew in marginal conditions such as aridity or semi-aridity where the ring growth is more sensitive to the environment, rather than in humid areas where tree-ring growth is more uniform (complacent). In addition, some genera of trees are more suitable than others for this type of analysis. For instance, the bristlecone pine is exceptionally long-lived and slow growing, and has been used extensively for chronologies still-living and dead specimens of this species provide tree-ring patterns going back thousands of years, in some regions more than 10,000 years.  Currently, the maximum span for fully anchored chronology is a little over 11,000 years B.P.
In 2004 a new radiocarbon calibration curve, INTCAL04, was internationally ratified to provide calibrated dates back to 26,000 B.P. For the period back to 12,400 B.P., the radiocarbon dates are calibrated against dendrochronological dates.  
Dendrochronology practice faces many obstacles, including the existence of species of ants that inhabit trees and extend their galleries into the wood, thus destroying ring structure.
European chronologies derived from wooden structures initially found it difficult to bridge the gap in the fourteenth century when there was a building hiatus, which coincided with the Black Death,  however there do exist unbroken chronologies dating back to prehistoric times, for example the Danish chronology dating back to 352 BC. 
Given a sample of wood, the variation of the tree-ring growths not only provides a match by year, but can also match location because climate varies from place to place. This makes it possible to determine the source of ships as well as smaller artifacts made from wood, but which were transported long distances, such as panels for paintings and ship timbers.
Radiocarbon dating calibration Edit
Dates from dendrochronology can be used as a calibration and check of radiocarbon dating.  This can be done by checking radiocarbon dates against long master sequences, with Californian bristle-cone pines in Arizona being used to develop this method of calibration as the longevity of the trees (up to c.4900 years) in addition to the use of dead samples meant a long, unbroken tree ring sequence could be developed (dating back to c.6700 BC). Additional studies of European oak trees, such as the master sequence in Germany that dates back to c.8500 BC, can also be used to back up and further calibrate radiocarbon dates. 
Dendroclimatology is the science of determining past climates from trees primarily from the properties of the annual tree rings.  Other properties of the annual rings, such as maximum latewood density (MXD) have been shown to be better proxies than simple ring width. Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous.
Art history Edit
Dendrochronology has become important to art historians in the dating of panel paintings. However, unlike analysis of samples from buildings, which are typically sent to a laboratory, wooden supports for paintings usually have to be measured in a museum conservation department, which places limitations on the techniques that can be used. 
In addition to dating, dendrochronology can also provide information as to the source of the panel. Many Early Netherlandish paintings have turned out to be painted on panels of "Baltic oak" shipped from the Vistula region via ports of the Hanseatic League. Oak panels were used in a number of northern countries such as England, France and Germany. Wooden supports other than oak were rarely used by Netherlandish painters. 
Since panels of seasoned wood were used, an uncertain number of years has to be allowed for seasoning when estimating dates.  Panels were trimmed of the outer rings, and often each panel only uses a small part of the radius of the trunk. Consequently, dating studies usually result in a "terminus post quem" (earliest possible) date, and a tentative date for the arrival of a seasoned raw panel using assumptions as to these factors.  As a result of establishing numerous sequences, it was possible to date 85–90% of the 250 paintings from the fourteenth to seventeenth century analysed between 1971 and 1982  by now a much greater number have been analysed.
A portrait of Mary, Queen of Scots in the National Portrait Gallery, London was believed to be an eighteenth-century copy. However, dendrochronology revealed that the wood dated from the second half of the sixteenth century. It is now regarded as an original sixteenth-century painting by an unknown artist. 
On the other hand, dendrochronology was applied to four paintings depicting the same subject, that of Christ expelling the money-lenders from the Temple. The results showed that the age of the wood was too late for any of them to have been painted by Hieronymus Bosch. 
While dendrochronology has become an important tool for dating oak panels, it is not effective in dating the poplar panels often used by Italian painters because of the erratic growth rings in poplar. 
The sixteenth century saw a gradual replacement of wooden panels by canvas as the support for paintings, which means the technique is less often applicable to later paintings.  In addition, many panel paintings were transferred onto canvas or other supports during the nineteenth and twentieth centuries.
The dating of buildings with wooden structures and components is also done by dendrochronology dendroarchaeology is the term for the application of dendrochronology in archaeology. While archaeologists can date wood and when it was felled, it may be difficult to definitively determine the age of a building or structure in which the wood was used the wood could have been reused from an older structure, may have been felled and left for many years before use, or could have been used to replace a damaged piece of wood. The dating of building via dendrochronology thus requires knowledge of the history of building technology.  Many prehistoric forms of buildings used "posts" that were whole young tree trunks where the bottom of the post has survived in the ground these can be especially useful for dating.
- The Post Track and Sweet Track, boardwalks or timber trackways, in the Somerset levels, England, have been dated to 3838 BC and 3807 BC.  where in Prehistoric Ireland a large structure was built with more than two hundred posts. The central oak post was felled in 95 BC. 
- cliff dwellings of Native Americans in the arid U.S. Southwest. 
- The Fairbanks House in Dedham, Massachusetts. While the house had long been claimed to have been built circa 1640 (and being the oldest wood-framed house in North America), core samples of wood taken from a summer beam confirmed the wood was from an oak tree felled in 1637–8, as wood was not seasoned before use in building at that time in New England. An additional sample from another beam yielded a date of 1641, thus confirming the house had been constructed starting in 1638 and finished sometime after 1641 . 
- The burial chamber of Gorm the Old, who died c. 958,  was constructed from wood of timbers felled in 958.  , where, between the tenth and the fifteenth century, numerous consecutive layers of wooden log pavement have been placed over the accumulating dirt. 
There are many different file formats used to store tree ring width data. Effort for standardisation was made with the development of TRiDaS.   Further development led to the database software Tellervo,  which is based on the new standard format whilst being able to import lots of different data formats. The desktop application can be attached to measurement devices and works with the database server that is installed separately. 
Herbchronology is the analysis of annual growth rings (or simply annual rings) in the secondary root xylem of perennial herbaceous plants. Similar seasonal patterns also occur in ice cores and in varves (layers of sediment deposition in a lake, river, or sea bed). The deposition pattern in the core will vary for a frozen-over lake versus an ice-free lake, and with the fineness of the sediment. Sclerochronology is the study of algae deposits.
Some columnar cacti also exhibit similar seasonal patterns in the isotopes of carbon and oxygen in their spines (acanthochronology). These are used for dating in a manner similar to dendrochronology, and such techniques are used in combination with dendrochronology, to plug gaps and to extend the range of the seasonal data available to archaeologists and paleoclimatologists.
A similar technique is used to estimate the age of fish stocks through the analysis of growth rings in the otolith bones.
Speakers Corner for archaeology? Major new line-up will hold the space for challenging conversations
The role of history, heritage, and archaeology in our lives and society is increasingly in the headlines and at the centre of conversations. DVIP Speakers Corner is a major new series of online talks that will explore how different the knowledge we gain from the past can be, when examined with new methods and ethical frameworks, or from new perspectives.
From climate change to gender, upcoming talks will rip straight into the headlines to explore the big ideas we hold about the past, and hold the space for challenging conversations with change-making archaeologists. Because when it comes to archaeology, context is everything.
Hosted by DigVentures, and supported by National Lottery Heritage Fund, all talks will be free to attend. Starting with Martin Carver, lead archaeologist at Sutton Hoo from 1983-2005, the first talk will head straight into the hot topic of how our understanding of the iconic ship burial has changed in the 80+ years since the famous excavation portrayed in Netflix’s recent blockbuster film, ‘The Dig’.
Sutton Hoo is a perfect example of how social context often drives the stories we tell about the past. The conclusions drawn from Basil Brown’s work and the 1930s have evolved, thanks to new excavations and new evidence, but also new and more ambitious research questions. What archaeologists now think and understand about this period of time, and its people, has changed dramatically as a result.
As well as revealing things the Netflix movie never showed, ‘Deeper Than The Dig, with Martin Carver’ will examine how social context changes the questions we ask, the results we get, and whether we’re willing to let it challenge what we think we know about the past, and what that means about who we are today.
It will talk explore how our understanding of the site, the people who created it, and the stories we tell about them, has changed over the last eight decades. What has driven the development of our ideas? Which ones have stuck? And what would archaeologists still like to know?
When understanding of the past underpins so many aspects of culture and daily life, DVIP Speakers Corner is a major new line-up of talks that will help to put the big questions in perspective.
DVIP Speakers Corner begins on Friday 14 May 2021 with more events to be announced throughout the year, whenever the lightning strikes! Make sure you stay tuned…
How a Midden Forms
Middens had multiple purposes in the past and still do. At their most basic, middens are places where rubbish is placed, out of the way of normal traffic, out of the way of normal sight and smell. But they are also storage facilities for recyclable objects they can be used for human burials they can be used for building material they can be used to feed animals, and they can be the focus of ritual behaviors. Some organic middens act as compost heaps, that improve the soil of an area. A study of Chesapeake Bay shell middens on the Atlantic coast of the United States by Susan Cook-Patton and colleagues found the presence of middens significantly enhanced local soil nutrients, especially nitrogen, calcium, potassium, and manganese, and to have increased soil alkalinity. These positive improvements have lasted for at least 3,000 years.
Middens can be created at the household level, shared within a neighborhood or community, or even associated with a specific event, such as a feast. Middens have different shapes and sizes. The size reflects how long a particular midden was used, and what percentage of material stored in it is organic and decays, as opposed to non-organic material which does not. In historic farmsteads midden deposits are found in thin layers called "sheet middens", the result of the farmer throwing out scraps for the chickens or other farm animals to pick over.
But they can also be enormous. Modern middens are known as "landfills," and in many places today, there are groups of scavengers who mine the landfills for recyclable goods (see Martinez 2010).
15 of the Best Journals by Our Reporters Around the World
Journals, a fixture of the international section, allow correspondents to step back from the news and write about places that intrigue them. We hope you enjoy our choices.
“I made sure to tell him not to tell his mama,” he said.
His wife, Anna Maria Sanò, soon became suspicious. “We had all these dirty clothes, every day,” she said. “I didn’t understand what was going on.”
After watching the Faggiano men haul away debris in the back seat of the family car, neighbors also became suspicious and notified the authorities. Investigators arrived and shut down the excavations, warning Mr. Faggiano against operating an unapproved archaeological work site. Mr. Faggiano responded that he was just looking for a sewage pipe.
A year passed. Finally, Mr. Faggiano was allowed to resume his pursuit of the sewage pipe on condition that heritage officials observed the work. An underground treasure house emerged, as the family uncovered ancient vases, Roman devotional bottles, an ancient ring with Christian symbols, medieval artifacts, hidden frescoes and more.
“The Faggiano house has layers that are representative of almost all of the city’s history, from the Messapians to the Romans, from the medieval to the Byzantine time,” said Giovanni Giangreco, a cultural heritage official, now retired, involved in overseeing the excavation.
City officials, sensing a major find, brought in an archaeologist, even as the Faggianos were left to do the excavation work and bear the costs. Mr. Faggiano also engaged in extensive research into the eras tiered below him. The two older sons, Marco and Andrea, found their lives interrupted by their father’s quest.
“We were kind of forced to do it,” said Andrea, now 34, laughing. “I was going to university, but then I would go home to excavate. Marco as well.”
Mr. Faggiano still dreamed of a trattoria, even if the project had become his white whale. He supported his family with rent from an upstairs floor in the building and income on other properties.
“I was still digging to find my pipe,” he said. “Every day we would find new artifacts.”
Years passed. His sons managed to escape, with Andrea moving to London. City archaeologists pushed Mr. Faggiano to keep going. His own architect advised that digging deeper would help clear out sludge below the planned bathroom, should he still hope to open his trattoria. He admits he also became obsessed.
“At one point, I couldn’t take it anymore,” he recalled. “I bought cinder blocks and was going to cover it up and pretend it had never happened.
Today, the building is Museum Faggiano, an independent archaeological museum authorized by the Lecce government. Spiral metal stairwells allow visitors to descend through the underground chambers, while sections of glass flooring underscore the building’s historical layers.
His docent, Rosa Anna Romano, is the widow of an amateur speleologist who helped discover the Grotto of Cervi, a cave on the coastline near Lecce that is decorated in Neolithic pictographs. While taking an outdoor bathroom break, the husband had noticed holes in the ground that led to the underground grotto.
“We were brought together by sewage systems,” Mr. Faggiano joked.
Mr. Faggiano is now satisfied with his museum, but he has not forgotten about the trattoria. A few years into his excavation, he finally found his sewage pipe. It was, indeed, broken. He has since bought another building and is again planning for a trattoria, assuming it does not need any renovations. He has no plans to lift a shovel.
Dating techniques fall into two categories, relative and absolute. Relative dating techniques (1) ordinally rank strata relative to one another through time (see Figure 1.6) or (2) use what is known about deposits in one area, such as volcanic ash or lava, to relatively date deposits in another area. Jefferson is credited with the Law of Superposition, which posits that as you go deeper into the earth, layers get older, as long as strata have not been disturbed due to human, animal, or geological activity. Thus artifacts or fossils found in one layer are either older or younger than those in a deeper or shallower layer, respectively. Absolute dating techniques use similarities in (1) floral and faunal assemblages or (2) sedimentary and/or chemical composition of deposits in order to match those of unknown age with those of known age and/or order the progression of environments, organisms, and climatic and geological activity within or between regions.
Diagram illustrating cross-cutting relations in geology. These relations can be used to give structures a relative age. Explanations: A – folded rock strata cut by a thrust fault B – large intrusion (cutting through A) C – erosional angular unconformity (cutting off A & B) on which rock strata were deposited D – volcanic dyke (cutting through A, B & C) E – even younger rock strata (overlying C & D) F – normal fault (cutting through A, B, C & E). Cross-cutting relations by Woudloper is licensed CC-BY-SA.
Absolute or chronometric dating techniques yield approximate dates in years BP (before the present) or BCE (before the Common Era). BCE and CE (Common Era) retain the BC/AD system of dating without the religious connotation. An abbreviated way to refer to a certain number of years ago, especially when considering the fossil record, is kya or mya (thousands or millions of years ago, respectively), thus eliminating all of those ungainly zeroes! While BP makes more sense in that you do not need to add 2,000+ years to the date, most people are accustomed to the BC/AD system, thus explaining the common use of BCE. The best-known absolute dating techniques are radiometric dating methods, for example, Carbon-14 ( 14 C). They are used to measure the half-life or replacement of radioactive elements in organic or fossil material or the layers in which they are found. Since those methods are time-limited and/or context-specific, the most appropriate technique(s) must be chosen based on a variety of parameters. The following techniques use radioactive decay for dating purposes:
[NOTE: For more information on the following methods, consult Henke and Tattersall (2006), Handbook of Paleoanthropology and/or Davis (2009), “Other Dating Methods”: http://www.geo.arizona.edu/palynology/geos462/11datingmeth.html.]
Carbon-14 dating (≤60 kya) measures the remaining 14 C in organic materials (i.e., carbon-containing). Since plants use carbon dioxide for photosynthesis, they contain all three isotopes of carbon ( 12 C, 13 C, and 14 C) in the approximate ratios present in the atmosphere. Animals eat plants and thus, at any particular time, they will all have approximately the same amount of 14 C. Once they die, they no longer accumulate carbon. The level of the more stable 12 C can then be compared to the remaining 14 C in organic remains to determine when they died. The half-life of 14 C is
5,700 years, that is, half of the 14 C will have been lost in a specimen in that amount of time.
Uranium series dating (≤500 kya) examines the relative levels of two elements, Uranium-234 and Thorium-230, resulting from the former’s decay into the latter. It is used to date calcium carbonate in coral and shells.
Potassium-Argon (K/Ar) and Argon-Argon (Ar/Ar) dating both measure the ratio of one isotope to another via the process of radioactive decay, Potassium-40 → Argon-40 and Argon-40 → Argon-39, respectively. They are often used to date volcanic layers but can also be used on other soil components, such as clay. While the age range for both methods may be reported to be unlimited, K/Ar dating is not useful for “young” materials because the half-life of potassium is so long—1.26 billion years.
Other methods that also rely on radioactivity are:
Electron spin resonance (ESR) (up to “a few” mya) examines the pattern of electrons that have “spun” out of their original location in mineral compounds (e.g., calcium compounds), leaving empty spaces behind, due to exposure to environmental radiation. Tooth enamel is the most useful application of ESR in paleoanthropology, but ESR can also be used to date quartz particles in sediments (Wagner 2006).
Fission track dating (20 mya—>10 kya) measures the number of “tracks” (pitting) in mineral compounds that result from the energy released when Uranium-238 spontaneously fissions over time. This method can be used to date a variety of minerals, such as mica, as well as products of volcanic (e.g., obsidian) and meteoric activities (Davis 2009 Wagner 2006).
Apatite crystals can be used in fission-track dating. “Apatite crystals” by OG59 is in the public domain.
Thermoluminescence (300–1 kya) measures radioactive decay particles in mineral compounds. It is useful for compounds that were exposed to intense heat (e.g., volcanic eruption) at some known point in time, when the “radioactive clock” was reset to zero and decay began anew. Thermoluminescence can be used to date artifacts (e.g., ceramics) and features (e.g., hearths), as well as products of sedimentation (e.g., speleothems, which are mineral deposits that form in caves) and volcanic activities (e.g., tephra, which are fragments from volcanic eruptions) (Davis 2009).
The following methods do not rely on radioactive activity but rather organic processes:
Dendrochronology uses tree rings in fossil or charred wood to date artifacts or fossils found in association with the wood. Each year, trees produce a new layer of peripheral tissue. When climatic conditions are favorable, more tissue is deposited and a thicker ring results, and vice versa. A cross-section of the tree tells the history of its growth (see Figure 1.8). However, in order to use dendrochronology as a dating method, a chronology (temporal record) needs to be constructed for a given region, in this case a map of the annual growth rate back through time. Living trees and dead wood can be used as long as there is overlap in ring patterns between them.
Dendrochronology: tree ring dating. “Dendrochronologie” by Stefan Kühn is licensed under CC BY-SA 3.0.
Amino acid racemization (2 mya–2 kya ± 15%) measures the ratio of two forms of an amino acid, one produced while an organism is alive and the accumulation of a second form after death. If the ambient temperature at the time of death can be approximated, the specimen can be dated and vice versa (Davis 2009).
Paleomagnetism (hundreds of thousands–millions of years, Fagan 2000) measures past changes in the earth’s paleomagnetic fields that are preserved in some common minerals found in rocks and sediments. Since scientists have established a chronology of those changes, the materials can then be given approximate dates as to when they formed. When paleomagnetism is used to date archaeological materials, it is termed archaeomagnetic dating.
Obsidian hydration (100–1 mya) is used to date volcanic glass, that is, obsidian, by examining the amount of hydration that has occurred due to exposure to the elements. It is useful in dating obsidian artifacts as well as glacial and volcanic activities (Davis 2009).