In fact, several dozen classical authors in the first millennium BC ordered time as a succession of ages based on technological progress. A three-age system encompassing the Stone, Bronze, and Iron Ages was the most common time-sorting methodology, but there were variations with copper and gold. Lucretius BC summarized these Western views of dating the past. The principle of a systematic organization of ex situ archaeological materials started with the understanding of the three-age system in the 16th century by Michael Mercati , who was the superintendent of the Vatican gardens and adviser to Pope Clement VIII.
Principles of Prehistoric Archaeology. Chronology: Relative and Absolute Dating methods
The combination of his Renaissance education, his substantial mineral and fossil collections, and his access to the newly acquired American ethnographic artifact collections permitted Mercati to formulate the foundations of modern archaeology. His observations, which were not easily accessible until the 18th century, are all the more remarkable when one considers the intellectual milieu of that era.
In Europe during this era, inquiry into the prehistoric past was discouraged, because the Bible was regarded as the supreme authority on human history and the early history of the earth. For example, creationism dominated scholarly writings on the origin of the universe and humanity, and during this period, fossils of marine organisms that were sometimes found in mountains were described as being washed up by the Great Flood.
Ancient arrow points and other prehistoric stone tools were thought to have been produced by thunderbolts and other natural phenomena.
Prehistoric stone arrow points and axes were believed to have fallen from the sky at the moment when thunder stuck. These implements were called thunder-stones, ceraunia, or pierre de foudre. It generally was believed that all living plant and animal species were survivors of the Great Flood and that with careful biblical research, especially on the book of Genesis, it was possible to calculate the age of the earth.
For example, in , Dr. John Lightfoot, the vice-chancellor of Cambridge University, calculated that the universe was created in BC, on October 23, at 9: Later in , Archbishop James Ussher refined this estimate and suggested that the earth was actually created on the evening preceding October 23, BC. This is the kind of pedantic to us debate that took place, so that although historical sites were being studied, prehistoric archaeology was being interpreted in light of the Bible.
But, in situ materials also required theory for relative sorting, and this was provided by the Danish atomist and geologist Bishop Nicholas Steno In a sedimentary sequence, the older beds are on the bottom, and the younger beds are on the top; the Principle of Original Horizontality: Sediments tend to be deposited in flat, horizontal layers; and the Principle of Original Lateral Continuity: Through human ingenuity, the last years have been witness to great number of techniques for sorting time applicable to the scientific study of the past.
These various dating techniques fall into one or more of three categories: Absolute techniques of varve analyses and dendrochronology are only such when they can be clearly calibrated to a known year; in all other cases, they are relative dating techniques. Some techniques for example, obsidian hydration, archaeomagnetism require a radiometric technique for calibration; all benefit from their use.
- Dating Methods.
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- Dating methods.
Radiocarbon is the best known of the radio-metric techniques and is in fact an established method that relies only on the decay of an isotope 14C formed from the outer-atmosphere comic-ray-generated neutron bombardment of Nitrogen 14N without reference to daughter production. In this respect, it is the most straightforward of the radiometric dating techniques.
Dating Techniques | symazoxahago.tk
Living organisms incorporate 14CO2 and maintain an equilibrium until death, at which time the radiocarbon clock begins to tick as the 14C decays exponentially with a rate known as the Libby half-life 5, years. A simple ratio measurement of the amount of 14C remaining versus the amount present when the organism left the living biomass yields a radiocarbon age, which can be converted to calendrical years with a dendrochronological curve that corrects for the cosmic ray fluctuations that have taken place in the past.
This ratio of original-to-remaining 14C is obtained in one of two ways: The atom-counting method affords an advantage in some dating situations for example, shorter counting times, smaller sample sizes, no cosmic ray backgrounds, and the extension of the age range from less than 40, years to 70, years. These techniques tend to have an age range orders of magnitude greater than radiocarbon for example, age of the Earth , because they use half-lives that are very long in comparison to radiocarbon tU forK: Thermoluminescence TL , electron spin resonance ESR , and fission track are dating techniques that rely on the accumulation of radiation damage in materials from the decay of radioactive isotopes.
TL and ESR depend on the , , and , decay of 40K, U, U, and Th in the natural environment and the consequent buildup of age information in the form of trapped electrons removed from their valence bands by the ionizing radiation. TL recovers this information by heating the sample or by optically measuring the trapped energy, or optically stimulated luminescence OSL.
ESR identifies radicals that have been formed by ionizing radiation in liquids and solids and electron traps in minerals. ESR measurement is accomplished by applying a microwave frequency to the sample that permits the amount of radiation damage to be quantified. The radiation environment within which a sample was exposed must be known well for both TL and ESR to be effective techniques.