Modern Archaeological Techniques
Sites are located with ariel surveys and satellite imagery. Satellite images sometimes reveals the outlines of temples, towns and trade routes obscured by sands or vegetation cover or sites that are otherwise missed on the ground. Multi-spectral light-imaging technology, designed for NASA for the study on planet surfaces, has made it possible to read papyrus scrolls badly burned in the eruption of Pompeii. Using extremely sensitive filters, scientists are able to see black ink written on the burnt black papyrus.
Sometimes small camera are inserted into tombs. First a hole is drilled and a tube is inserted and the camera is inserted through the tube. An effort is made to make sure the interface is airtight so that no air or contaminants enter the burial chamber.
Magnometers and metal detectors are used to search for metal objects under the surface. Archaeologists can also send electric currents through the ground at depths of a few foots. By observing differences in the resistance to current they can record differences in subsurface densities and determines what is below: foundations, pavement or just dirt. This helps locate buildings and determines the lay out of settlements.
Ultrasound and seismic generating machines are now being used by Egyptologists to locate temples and ruins covered by sand. Scientists are also using theodolites, electric distance measurers and the technique of photogrammetry. They shoot seismic waves through the sand and the through the monuments. Magnetometers are used to detect tombs. The underground radar does not work well when water is present.
CT scan for the IcemanMummies are being scanned with CT (computerized tomography) technology to determine their age, sex and cause of death and whatever else can be gleaned from them. With this technique the mummy is X-rayed at different angles to produce a 3-D composite image of the entire body. One advantages of such scans is the mummy does not have to be unwrapped. The details are better than those of X-rays. Using this technique archaeologists and specialists check for evidence of trauma, vitamin deficiencies, degenerative diseases.
Foods and drinks from ancient times can be determined by analyzing samples in a spectrometer and looking for organic compounds, especially long-chain lipids, triglycerides and fatty acids that characterize many foods. The presence of beer can be determined by the presence of calcium oxalate (“beerstone”). Wine can be determined by tartaric acid and its salts. Samples can be extracted from pottery and jars with solvents. Specific fatty acids can be markers for meat such goat, mutton and pork. Anisic acid is an indicator of anise, or fennel.
Pollen grains of specific species have vary distinctive shapes and surface patterns. They can be easily identified under a microscope and scientists can use them to date objects and describe the habitats of objects that contain them. By identifying ancient seeds and pollen archaeologists can figure what people ate and drink and get some insight into weather patterns in ancient times. Archaeologists can also figure out trade patterns by analyzing the chemicals in paint and vegetable dyes found in scraps of clothes.
Underwater archaeologists use sonar and multibeam bathymetric technology to scan the sea floor and send down remote control camera. Doing excavations of shipwrecks and ruins below about 50 meters is very difficult and expensive because those depths are beyond the reach of divers who can work any great length of time. See Bronze Age Ship, Romans, Greeks
Dating Methods
Historical records only go back to around 2000 B.C. Dating of ancient Egypt, and Sumer was done by examining written records of the durations of reins of kings. By working backwards archaeologists came up with the date of 3000 B.C. when those civilizations first evolved."^
Ancient icons are indispensable archaeological tools. Minted to record a major historical event or the deification of an emperor of major figure, they can help scholar date objects and layers with some precision and provide important information on trade and political ties. Coins are used in a similar fashion. The oldest coins with dates to around 700 B.C.
Sometimes geologists can help date objects by measuring the amount of rain wear in cracks, alluvial deposits by streams and glaciers and layers of silt in lakes. Lichenometry is useful in measuring lichens from 100 and 9,000 years old.
Alexander Marshak identified the Ishango Bone. Afterwards he investigated scratched pebbles and other materials from the last Ice Age in EUROPE and discovered inconclusive evidence of time-keeping [time factoring] as far back as about 45000 years.
See Pottery, Above
Thermolumiscence and Optically Simulated Luminescence
australopithecus sediba endocast Thermolumiscence counts the number of electrons trapped in the microscopic crystal structure of a burned flint tool or other objects that to have been exposed to early-man-produced heat. By measuring the trapped electrons, the time when an object was last heated can be estimated. The method is useful in measuring minerals and natural glass between 0 and 500,000 years old.
The science behind thermolumiscence is the following: When minerals and natural glass are heated to a certain point radioactive atoms surrounding and buried inside crystals can release particles than can knock electrons out of their orbits. The released electrons sometime get stuck in defects in the crystal structure and over time the crystal fills with electrons at a regular, measurable rate. The trapped electrons are measured by reheating the material. As the trapped electrons escape they release light. By measuring that light scientists can count the trapped electrons and determine the age of the material.
Optically simulated luminescence is used to determine when minerals such as quartz are buried under sand or sediments by determining when they were last exposed to sunlight. This method operates under the same principals as thermolumiscence: by measuring the trapped electrons, the time when an object was last exposed to sunlight can be estimated. The trapped electrons are measured by firing beams of photons at the object. As the trapped electrons escape and return to their atoms they release heat. My measuring the heat scientists can count the trapped electrons and determine the age of the material.
Optically simulated luminescence is useful in measuring minerals and natural glass between 0 and 500,000 years old. The trick is to find objects that have not been exposed to sunlight and prevent them from being exposed to sunlight. Just of few seconds of exposure to sunlight can cause the trapped electrons to break from the crystals and return to their original state. Scientists who rely on this methods can not look for fossils and objects in the normal way in the sunlight. They hammer hollow, stainless steel cylinders into the sand and capped them and later examine their finds in a darkroom and fire beams of photons their samples to release the trapped electrons.
Carbon 14 Dating
taking a sample of a mummy's tooth
Carbon is useful in measuring minerals, shell, bone, wood, teeth and charcoal between 0 and 40,000 years old. After a living things dies that ratio of carbon 14 isotopes to carbon 12 isotopes decays at a known rate. By measuring the change in ratio of unstable carbon 14 to stable carbon 12 an organic material can be dated. Fossils over 40,000 years have so little carbon 14 left the method is no longer accurate.
Radiocarbon 14 dating was pioneered in the 1940s by University of Chicago chemist Willard Frank Libby, who won the Nobel Prize for his work. Carbon 14 is an unstable radioactive isotope produced when cosmic particles from space slam into nitrogen atoms in the upper atmosphere. Living plants and animals absorb Carbon 14 and other kinds of carbon from carbon dioxide in atmosphere.
When a plant or an animal dies it can no longer absorb carbon. The carbon 14 then begins to revert back to regular carbon (Carbon 12) at a known rate. The amount of Carbon 14 in a sample can thus be used to determine the date the sample died, or in other words when it stopped absorbing carbon.
Carbon 14 has a half life of 5,730 years. This means that after 5,730 years the amount of carbon 14 in an object is reduced by half as the carbon 14 changes to nitrogen 12. After another 5,730 years half of the remaining amount of carbon 14 decays by half again so that only one quarter of the original amount is left---and so on until about 40,000 years when only negligible amounts of carbon 14 is left.
With Carbon 14 dating, a sample of the material to be dated---for example, charcoal from a hearth, a piece of wood from a ship beam, a seed in a strata of soil---is burned and reduced to pure carbon. The ratio of Carbon 14 to Carbon 12 can be measured with a high energy mass spectrometer, revealing the date. Carbon dating can be used to date even minute samples of something such as residue on pots or pigments.
Problems with Carbon Dating
David Silverman of Reed College wrote: “Carbon 14 dating tends not to be very helpful to archaeologists (more so to geologists and the like). Carbon-14 dating only works on items which contain carbon, such as wood or coal. And in some cases C-14 dating can tell you only when an object's raw material first came into existence, as opposed to what you really want to know, which is when the material was shaped into its current form. [Source: David Silverman, Reed College, Classics 373 ~ History 393 Class ]
Over the millennia the amounts of Carbon 14 in the atmosphere have not been constant. This means that in certain period a given organism can absorb more or less Carbon 14 depending on how much is in the atmosphere. Fortunately some trees, such as bristlecone pines in California live a long time, and their ages can be accurately measured using tree rings and Carbon 14 levels can be measured in each tree ring and thus a table has been produced that compensates for fluctuations in Carbon 14 levels during each year.
Short-lived plants such as grain are the best for dating. With wood there is always the problem that the tree was cut down long before it was incorporated into a site. In addition, Carbon 14 levels often vary greatly depending on which part of the tree the sample came from: deep inside the tree or on the outside.
Samples can also be contaminated with younger or older carbon brought it by groundwater, earthquakes or carbonate rocks such as limestone. Contamination can usually be eliminated with careful cleaning before the dating process begins. Even when all goes well, the dating does not produce a date but rather a probability that the sample falls within a certain range of dates.
Nondestructive Radiocarbon Dating
Nikhil Swaminathan wrote in Archaeology magazine, “Precisely dating archaeological artifacts is not as easy or harmless as it might seem. The most common method, radiocarbon dating, requires that a piece of an organic object be destroyed---washed with a strong acid and base at high temperature to remove impurities, and then set aflame. The resulting release of carbon dioxide is fed to an accelerator mass spectrometer, which measures the decay of radioactive carbon 14---the more the carbon 14 has decayed, the older the object is. [Source: Nikhil Swaminathan, Archaeology magazine, January/February 2011]
accelerator mass spectrometer, machine used to measure the carbon 14 decay in a sample
Over the past 20 years, chemist Marvin Rowe of Texas A&M University has developed a nondestructive method for carbon dioxide extraction. In his process, an object is placed in a vacuum chamber and a supercritical fluid---a hybrid gas/liquid---is applied as a solvent (as in dry cleaning). Next, Rowe passes plasma---an “electrically excited ionized gas”---over the artifact, which selectively strips carbon from the sample. “It's essentially like slowly burning the sample, so we can just oxidize a little off the surface and collect that carbon dioxide," explains Rowe. This year he further refined the method so it will work on objects coated in sticky hydrocarbons, such as the resins that cover Egyptian mummy gauze.
Thus far, he's dated samples of wood, charcoal, animal skin, bone from a mummy, and ostrich eggshell. “Everything so far that we've tried to do with the nondestructive technique has agreed statistically with regular radiocarbon dating," Rowe says, “and you basically don't see any change in the sample." R. E. Taylor, a radiocarbon expert at the University of California, Riverside, says Rowe's technique may have limitations, as items older than 10,000 years will have impurities that the technique may not be able to purge. Archaeologists, meanwhile, are hailing the discovery as one of the most important in decades, particularly for issues surrounding the repatriation of human remains from Native American burials, which modern tribes don't want to see harmed.
Rowe's refinement of carbon dioxide extraction dovetails with an update to the radiocarbon calibration curve, which increases the accuracy of radiocarbon dating by accounting for past fluctuations in carbon 14. According to researchers at Queen's University of Belfast, the new curve doubles the accuracy of dating as well as the age of artifacts on which it can be used, from 25,000 to 50,000 years.
Normally carbon samples are converted to acetylene gas by combustion in a vacuum line. The acetylene gas is then analyzed in a mass spectrometer to determine its carbon isotopic composition.
Tree Rings
bristlecone tree rings
Dendrochronology is useful in measuring tree rings from zero to 12,000 years old. Tree rings from bristlecone pines provide scale for correcting radio-carbon dating.
Every year trees lay down two layers---one broad and light colored during the growing season, the other dark in the winter when little growth occurs. The rings are not only useful in measuring age but also offer clues to what happens in given years. Each cross section of tree trunk has a distinct pattern of tree rings. Sometimes the rings have unusual growth patterns that occur during a particularly hot winter or cold summer or an event like a volcanic eruption.
With pieces of wood from trees that have been dead for centuries or millennia archaeologists often look for unusual patterns that indicate an event---like a volcanic eruption---that occurred on a known date and then count the tree rings from that event to determine the date of the artifact.
Artifacts dated using tree rings include logs used in the tomb of King Midas of the Phrygians, cut in 718 B.C." timbers from an Egyptian shipwreck that revealed a gold scarab with Queen Nefertari's name, cut in 1316 B.C." and logs of bronze age houses in Acemboyuk and Kultepe Turkey, cut in 1752 B.C. and 1810 B.C."
Many objects from the Mediterranean and Middle East have been dating by looking at structural timbers from trees that grew during the catastrophic eruption on the volcanic island of Thera in the Aegean Sea that occurred around 1500 B.C. and hurled vast amounts of material in the atmosphere and caused a cooler and wetter summer worldwide. Bristlecone pines from California and oak tress from Irish bogs have tree rings that are more tightly packed after the volcano erupted.
Wood doesn't preserve, stone does.
Determining the Age of Wine by Examining Traces on Potsherds
The earliest evidence of grape wine was found in clay pottery from Khramis Didi Gora, Georgia dated to to 6,000 B.C. Ashifa Kassam and Nicola Davis wrote in The Guardian: “A series of excavations in Georgia has uncovered evidence of the world's earliest winemaking, in the form of telltale traces within clay pottery dating back to 6,000 B.C. [Source: Ashifa Kassam and Nicola Davis, The Guardian, November 13, 2017 \+/]
“To explore whether winemaking was indeed a part of life in the region, the team focused on collecting and analysing fragments of pottery from two neolithic villages, as well as soil samples. Radiocarbon dating of grains and charcoal nearby suggested the pots date to about 6,000–5,800 BC. In total, 30 pottery fragments and 26 soil samples were examined, with the inside surface of the pottery ground down a little to produce a powder for analysis. While many of the pieces were collected in recent excavations, two were collected in the 1960s; researchers have long suspected they might bear traces of wine.The team then used a variety of analytical techniques to explore whether the soil or the inner surface of the vessels held signs of molecules of the correct mass, or with the right chemical signatures, to be evidence of wine. \+/
“The results, published in the Proceeding of the National Academy of Sciences, reveal that for eight of the fragments, including the two previously unearthed, the team found traces of tartaric acid – a substance found in grapes in large quantities. Tests on the associated soils largely showed far lower levels of the acid. The team also identified the presence of three other acids linked to grapes and wine. Other evidence indicating the presence of wine included ancient grape pollen found at the excavated sites – but not in the topsoil – as well as grape starch particles, the remains of a fruit fly, and cells believed to be from the surface of grapevines on the inside of one of the fragments. \+/
“While the team note that it is possible that the vessels were used to store something other than wine, such as the grapes themselves, they note that the shape of the vessels is suited to holding a liquid and that grapes or raisins would have degraded without trace. Moreover, there are none of the telltale signs that the pots were used for syrup-making, while grape juice would have fermented within a matter of days. \+/
accelerator mass spectrometer schematic for radiocarbon dating