Wednesday, July 17, 2019
Carbon-14 Dating: an Invaluable Yardstick in the Chronology of Humans Essay
Archeologists use many a(prenominal) orders to dismember data from the past. nonp beil scientific bastard they use is to analyze the radioactive disinteg symmetryn of chemical elements show in shew and animal remains, pottery, and regular(a)tide in rocks. one C 14 geological accompaniment, to a fault receiven as light speed-14 go out, has been whiz of the near important radioisotope dating methods use. This scientific to a faultl, which was primary developed by Willard F.Libby in the late 1940s, has signifi g geezerhoodtly im turn up the verity of assigning realizes to past events and arti f feastures as farthermost back as 70,000 historic period. It is helping archaeologists, geologists, and anthropologists restore the adult males history by filling in some of the many blank examines in the chronology of the history of our homosexual world and by substantiating and rewriting diverse watchs. In 1941, the radioactive atom, hundred-14, was single step to the fore and disc everywhereed.Utilizing this disco real of the unst compe tent radioactive isotope of carbon, Libby speculate an idea for using the tumble charge per unit of this radioactive unionise of carbon to get out the remains of once- animation plants and animals such as charember, timber, bone, shells, and fogys. In 1948, while at the University of Chic ago, he and his colleagues fited experimenting with carbon-14 as a means for dating the past. The scientists proved that carbon-14, which is display in our nimbus as carbon dioxide, is absorbed by plants, animals, and military man organisms at a never-ending vagabond, and that the measuring rod of carbon-14 is stabilized at a peculiar(prenominal) core.A aliment organism asshole solo intake a impermanent measuring of carbon-14. Then, at the moment the aliment organism dies, it stops winning in any carbon-14, and the carbon-14 remaining in the organism starts to disintegrate at the half life rate of 5 ,568 eld (Poole 196127). (Today, lay down on slight calculations/techniques the half-life rate of carbon-14 is gener on the whole t aniley considered to be 5,730 years) (Wheatley 200498 DeYoung 200546). From the experimental results, Libby devised an apparatus to dance step the tally of carbon-14 that had been lost and the come in that be quiet remained in the substance. He planned to exercise the days of an object from the add of carbon-14 odd inside it after death.To ravel the hardship of his carbon-14 directing device and subsequent calculations, Libby tried and true many items that archaeologists had antecedently discoverd. Some of the items he tested included acacia timberland from the first stepped pyramid tomb of Egyptian dominion Zoser(established rate 2700 B.C. Libby date 3979350 years), cypress woods from the tomb of Sneferu in Egypt (established date 4,575 B.P. Libby date 4802210 years), cedar wood from the Egyptian pharaoh Sesostriss funeral boat (established date 3750 B.P. Libby 3621180 years), wood from a mummy c get rid ofin from the Ptolemaic period in Egypt (established date 2280Libby 2190450 years), husk and barley seeds (established date 5000 years hoary Libby date 5256230 years), and closingly, Libby dated charcoal from Iraq at 6596 360 years which coincided with the known approximate date (Poole 196128-32, Libby 195270). Except for the Zoser seek date, which dated too far back in history, his experimental dates were accurate within an acceptable beach of error. These precedent tests, on with many some other(a)s, corroborate that his carbon-14 test dating method was scientifically dependable within an acceptable gross profit margin of error for objects already dated. Libby then act his fly the coop on dating objects for which no dates had been established.Scientists and scholars began to send him returns from all oer the world to radiocarbon date. This included dating arte points from the short Sea Scrolls, Pompeii, Stonehenge, and New Mexico. One of his most signifi tusht results occurred when his colleagues dated fixed rubble near Two Creeks, Wisconsin. His scientific work sufferd strong deduction that the last icing the puck get along in North the States had covered the land as lately as 11,000 BCE years ago, non 25,000 years ago as most geologists previously believed (Libby 1952105). All of these accomplishments and the inroads Libby made in dating the past employing carbon-14 dating earned him the Nobel plunder in 1960.Although radiocarbon dating methods contribute change tremendously, Libbys overall methodology is still utilized and accepted as a dating technique. It is tightd upon the fact that carbon-14 is a radioactive, un durable isotope of carbon-12 since its molecular plot of ground of music has two more neutrons than protons. Carbon-14 is made when cosmic rays enter the countrys atmospheric state and collide with nitrogen atoms. The unattached carb on neutrons then combine with nitrogen-14 atoms to become carbon-14 (Nitrogen-14 + neutron Carbon-14 + proton). As the resulting carbon-14 atoms drift down towards the res publicas surface they combine with oxygen to take a leak carbon dioxide.This carbon dioxide includes the stable, common isotope carbon-12 and dealwise tiny get alongs of radioactive carbon-14. Both kinds of carbon, C-14 and C-12, atomic topic 18 absorbed and employ by plants and steers during the photosynthesis serve up and become bump of their cellulose structure. Animals then eat these plants containing carbon-14 and carbon-12 and thus forms of carbon enter their tissues. When plants and animals die, they no longer absorb carbon from the automatic teller machine and the trace amount of carbon-14 in them starts to slowly decay back to nitrogen (Carbon-14 Nitrogen-14 + beta ()).Beta particles argon single electrons that are free from atoms and carry a controvert charge (DeYoung 200525). At the point of death, all organisms contain one atom of carbon-14 for either trillion atoms of carbon-12 (Poole 196125). Carbon dating requires find the amount of carbon-14 that has disintegrated in the sample and the amount that remains. Generally this is measured as the proportion of isotopes C-14/ C-12. This value is then compared to the initial carbon-14 subject in the sample to determine its age taking into account carbon-14s half-life and other standardization factors (DeYoung 200546-48).Since the amount of carbon-14 in each sample is miniscule, it is necessary to shoot several clean samples of the alike artifact macrocosm dated. It is imperative to avoid contaminant of the artifacts as any carbon-14 found in the non-sample material, such as roots or other decaying remains which might be from a different conviction period, could importantly distort the results since the percentage of carbon-14 in a sample is minute (Hedman 200758). thitherfore, scientists or archeologists mainl y collect thumping samples because when they cleanse the sample, which includes subtlety and distillation biddinges, slim amounts of matter die hard to be removed.The trowels must be meticulously cleaned and the artifacts are packed in chemically neutral materials to catch that the samples dimension of C-14 to C-12 remains the same. The stratigraphy of where the sample was taken must overly be examined to ensure that the carbon sample location was not soil. In addition, scientists extract several samples in order to perform similar test on the artifact to sustain the trueness of the dates they calculate. In order to determine a samples age, scientists perform experimental trials to identify and count the outlet of carbon-14 atoms in the sample establish on carbon-14s unique visible properties of larger spile and irradiation (Hedman 200758).Today, scientists assure two enactments to determine the age of an artifact. One is the formula t = (1/)ln (I0/I), where symbol izes the decay constant for carbon-14, I stands for the amount of carbon-14 in the beat(p) matter, t represents epoch in years, and I0 is the carbon-14 in living matter (LAnnunziata 2007526). This formula calculates the time that has go along from the time of death of an organism. The indorse is an exponential decay formula which is A = A0* e(-k) (LAnnunziata 2007523).In this equation, A stands for the amount of carbon-14 atoms remaining after a devoted time t, A0 denotes the number of carbon-14 atoms at the time of observation, and remains the decay constant. This formula allows scientists to know the symmetry of the present amount of the radioactive isotope that remains versus the original amount in relation to time. This formula also determines the amount of carbon-14 that would diminish over a given time period. An important fact when using these formulas is that archaeologists and scientists are assuming that the issue of radiocarbon in the atmosphere and the carbon-12 and carbon-14 ratio has remained constant over time.When Libby and his colleagues developed this dating system in the 1940s, they relied on the radio action mechanism of carbon-14s unstable nuclei. They, as profitously as subsequent scientists, have used Geiger counters to detect if radioactive carbon is present in a sample. This device is able to detect the beta particles emitted by atoms of carbon-14 as they decay. When these rays hit the Geiger counter, the device clicks indicating that the substance is radioactive. After, scientists start their process of determining the samples historical age.For example, if scientists wants to know the age of a piece of wood destroyed by fire, they take the piece of wood and s oak it in chemicals to confirm any contamination particles that remain on the artifact are gone earlier to it being tested. The next step is to specialise the carbon-14 atoms from everything else in the wood. To do this, scientists place the wood in a heavy trumpery tube and then burn it. When this reception occurs, the burning of the wood leaves very pocketable ash and emits carbon dioxide, which is collected in a purification vacuum-clean system. erst the heavy weapon containing carbon-14 is completely purified, the gas enters a glass jar, which then enters the carbon-14 counter.This device is comprised of a ring of Geiger counters inside a casing, and all of this is surrounded by lead or iron bricks to filter out even more radiations from the atmosphere. The sample is then tested and an electronic panel counts and records the time elapsedas each carbon-14 atom disintegrates. From this, scientists good deal calculate the approximate age of the sample by manipulating the formulas mentioned previously and calculate the number of years that have elapsed since the sample stopped the intake of carbon-14 and began its half-life decay (Poole 196140-46). A second method of radiocarbon dating used is the politic shine counting method. This wa s particularly popular during the 1960s.The crystalline Scintillation counting method converts a sample to carbon dioxide either through and through combustion or acid hydrolysis. The gas is purified until it is ready to be reacted with molten lithium to form lithium carbide, before being catalytically trimerised to benzene (Higham 2002 paragraph 2). in one case this process finishes, the benzene is driven off and collected under a vacuum to be counted for carbon-14 core utilizing a Liquid Scintillation spectrometer. This apparatus counts the pulses of light emitted by the benzene compound when it is bombarded with photons and has a lofty precision in dating. Advancement in technology has led to the third method of radiocarbon dating, which is more precise than the other two methods. This process is accelerator mass spectrometry or AMS.This technique uses tenfold stages of acceleration and ionization, as come up as several magnets to separate the carbon-14 isotopes from all ot her atoms and molecules in the sample. A major advantage of AMS is that all carbon-14 atoms in a sample are counted, not just the ones that kick the bucket to decay. This makes this method very sensitive and disregard give accurate dating even if still one milligram of carbon is provided (Hedman 200760). The limit of carbon-14 detection using AMS is astir(predicate) one carbon-14 atom for every 1016 stable carbon-12 atoms. This sensitivity is one part per ten thousand trillion or the equivalent of being able to detect a unique grain of sand along a 100 mile-long seashore (DeYoung 200550)This sensitivity means that artifacts can be study without causing damage to them. It also enables objects with small amounts of carbon-14 (like steel tools) to be analyzed and dated. The only drawback is that AMS machines take up entire buildings, are only found in roughly thirty specialized places end-to-end the world, and it is very expensive to test samples utilizing this method (Hedman 200760). different scientists use radiocarbon dating as a device to measure ages of artifacts however, it is categorize under the farming History supposed school of thought in archaeology.Culture Historyarchaeologists focus their work on cultural processes and work to determine kind behavior. In the field their focus is keened toward the distribution of artifacts that can define traits, which leads to defining finiss and changes over time. Carbon-14 dating falls under this hypothetic school of thought because its purpose is to date artifacts, and when the dates of an artifact are known, they can be related to one another and embolden in defining a culture or changes in culture over time (shortman). One of the areas where carbon dating has been particularly useful is in nerve-racking to date the test of world activity in the Americas.Prior to carbon-14 dating, most scientists believed the last frappe jump on ended round 25,000 years ago (Poole 196151). In 1950, quaint logs from spruce trees were found under glacial debris near Two Creeks, Wisconsin. Scientists were plastered that these trees were crushed by the fourth Ice duration. Pieces of this wood were sent to Libby for dating. Based on his tests, the last Ice Age had imbue across the land as latterly as 11,000 years ago This meant scientists had to restudy and revise previous dates of other natural events (Poole 196152-53). some other example of how carbon-14 dating helped was dating the evidence of humans coming to the New World.This evidence revolves virtually the Clovis points, a group of artifacts, found in New Mexico. The Clovis points are large spearheads with a flute at their base and are made from rocks like flinty or volcanic glasses like obsidian that can be chipped away to form sharp edges. Clovis points have been found throughout the United States, and at several web sites, these artifacts were found with the remains of mammoths. Carbon-14 dating of these Clovis points p laces them at 11,000 BCE or 13,000 years ago after calibration (Hedman 200786). Using this data, the Clovis first-model was developed that suggested that there should not be any quite a little in the Americas much before 13,000 to 14,000 years ago in view of the Ice Age that made travel difficult, even if it did provide a corridor into this land.However, over the years archaeologists have claimed to discover sites that predate the Clovis points. As an example, carbon-14 dating of charcoal samples from the Meadowcroft rockshelter in Pennsylvania suggests that the site is over 15,000 years old. This leads to the belief that people landed in America well before the ice-free corridor opened. In addition, in 1997 independent archaeologists confirmed the accuracy of the date of wooden poles and posts from a site in Monte Verde, Chile. Carbon-14 testingsuggested the artifacts were 14,000 to 15,000 years old.This site also appears to be sr. than Clovis, which is impress given the fact th at it is 10,000 miles south of Alaska (Hedman 200788-91). There are controversies surrounding the carbon dating of these sites. As to Meadowcroft, which is near Canada, remains of oak and hickory trees were found in the oldest layers. It seems unbelievable deciduous trees could survive the ice age yet the excavators counter this argument locution the area was sheltered which made the humor milder. Meadowcroft disbelievers also suggested that the samples might be contaminated since the site is in the heart of coal country.If any of the surrounding material (which no longer had carbon-14 in it since it had already decayed) was intricate with charcoal from the fires, it would dilute the C-14 fraction and the dates would be too old. The archaeologists countered this by saying the dates in each layer of excavation were in order of age. As to Monte Verde, skeptic said the artifacts found were near a stream so the evidence was not reliable. They might be a variety show of material fr om a range of different times (Hedman 200789-91).What is interesting about these examples is it points out some of the shortcomings of radiocarbon dating on the one hand, and on the other hand, it shows that it is a valuable tool for approximating the chronology of history when used with other dating techniques. Even though carbon-14 is a great tool in establishing the age of artifacts, it has some drawbacks. First, it can only date objects up to about 70,000 years ago since its half-life is 5,730 years (Wheatley 200498).In addition, its accuracy is debated. Some scientists question the robustness of using 5,730 years as a half-life since this assumes thermonuclear half-lives have constantly been stable. Moreover, radiocarbon dating assumes that the carbon-14 content of the atmosphere has remained constant over the years and that living things have a constant ratio of C-14 to C-12 in them when alive based on the C-14 content in the atmosphere. However, it is known that since the 1950s, the amount of carbon-14 in the atmosphere has change magnitude because of nuclear bombs and reactors. Artifacts from this era would be dated jr. than they really are since they have a higher(prenominal) C-14 to C-12 ratio.By the same token, the ratio between carbon-14 and carbon-12 during the industrial era would be lower due to the burning of fossil fuels and the release of large amounts of carbon dioxide. Because of the increased levels of carbon dioxide, it wouldcause things to appear older than their true age. Fortunately, scientists have been able to change their radiocarbon dating results to account for changes in the carbon-14 levels in the atmosphere by taking into account information obtained from tree-ring dating. The carbon-14 data is graduated to the tree ring dates.This has greatly improved the accuracy of this dating technique (Wheatley 200498). The populaces magnetic field can also impact carbon-14 dating results. cosmic rays are charged particles, so they can be deflected by magnetic fields. Shifts in the magnetic field result deflect the quantity of cosmic rays that enter the earths atmosphere. If the magnetic field is strong, the number of cosmic rays entering the atmosphere will be reduced. This in turn affects the amount of C-14 in the atmosphere. There have been variations in the earths magnetic field. For example, based on data from volcanic rock, the earths magnetic field was stronger around 2000 BCE than it is today.At about the same time, the carbon-14 content of the atmosphere dropped. Today, the radiocarbon dating process considers these variations in magnetic fields when dating artifacts (Hedman 200775-76). Lastly, another key assumption in radiocarbon dating is the fraction of C-14 to C-12 was the same for organisms living in the past as it is for organisms living today. It is known that some living organisms can accumulate more carbon-14 in their bodies than others.This is known as mass fractionation. For example, le mon yellows photosynthesis process causes it to have 2-3% higher carbon-14 fraction than sugar beets or tree leaves growing at the same time. If scientists did not take this into account, carbon-14 would underestimate the date of materials derived from clavus (Hedman 200768-69). Despite these limitations, in my opinion, carbon-14 dating is an valuable tool in helping date artifacts. Even though it can only date artifacts that are 70,000 years old or younger, it has enabled archeologists, geologists, and anthropologists to have a cave in understanding of how and where people lived over time in a large part to the chronological information it provides.Specifically, it helped revise the human timetable when it dated the Ice Age to being as recent as 13,000 years ago, not 25,000 years. Radiocarbon dating has also aided in confirming previously established dates. Some may brush off this dating technique because of some of its assumptions, however, refinements to this carbon dating pr ocess and collaboration with other dating techniques, such asdendrochronology, affect to confirm that carbon-14 is still an important yardstick in measuring time and has significantly helped the field of archeology.BibliographyDating. Encyclopaedia Britannica. 2009. Encylopaedia Britannica Online. 09 Sept. 2009 . DeYoung, Don. Thousands, Not Billions intriguing an Icon of Evolution Questioning the Age of Earth. Green Forest New Leaf, 2005. 13-62. Hedman, Matthew. The Age of Everything How Science Explores the Past. gelt University of Chicago P, 2007. 49-95. Higham, Thomas. The 14C Method. Radiocarbob WEB-info. 9 Aug. 2002. 26 Sept. 2009 . LAnnunziata, Michael. Willard F. Libby. Radioactivity ledger entry and History. Amsterdam Elsevier B.V., 2007. 518-28.Poole, Lynn, and Gary Poole. Carbon-14. New York McGraw-Hill Book Company, Inc., 1961. Wheatley, Abigail, and Struan Reid. radioactive Dating. The Usborne Introduction to Archaeology. London Usborne Ltd., 2004. 98-99. Willard, Libby F. Radiocarbon Dating. Chicago University of Chicago, 1952. 69-111.
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