Friday, May 24, 2019
Carbon-14 Dating: an Invaluable Yardstick in the Chronology of Humans Essay
Archeologists use many manners to fail data from the past. One scientific pecker they use is to analyze the radioactive decay of chemical elements nominate in plant and animal remain, pottery, and even in rocks. Radio vitamin C date, also known as degree centigrade-14 dating, has been one of the near important radioisotope dating methods used. This scientific musical instrument, which was first developed by Willard F.Libby in the late 1940s, has signifi crumbtly improved the accuracy of assigning dates to past events and artifacts as remote back as 70,000 days. It is helping archaeologists, geologists, and anthropologists reconstruct the worlds history by filling in whatever of the many blank dates in the chronology of the history of our human world and by substantiating and revising other dates. In 1941, the radioactive atom, blow-14, was isolated and discovered.Utilizing this disco very(prenominal) of the unstable radioactive isotope of carbon, Libby recipeted an ide a for apply the decay rate of this radioactive form of carbon to date the remain of once-living plants and animals such as charcoal, timber, bone, shells, and fossils. In 1948, while at the University of Chicago, he and his colleagues started experimenting with carbon-14 as a means for dating the past. The scientists proved that carbon-14, which is pre direct in our atmosphere as carbon dioxide, is absorbed by plants, animals, and human beings at a unalterable rate, and that the standard of carbon-14 is stabilized at a specific keep down.A living organism back whole intake a finite totality of carbon-14. Then, at the min the living organism dies, it stops taking in any carbon-14, and the carbon-14 remaining in the organism starts to disintegrate at the half-life rate of 5,568 years (Poole 196127). (Today, found on refined calculations/techniques the half-life rate of carbon-14 is generally considered to be 5,730 years) (Wheatley 200498 DeYoung 200546). From the experiment al results, Libby devised an apparatus to measure the numerate of carbon-14 that had been lost and the amount that still remained in the substance. He planned to calculate the historic period of an object from the amount of carbon-14 left inside it after death.To test the validity of his carbon-14 counting crook and subsequent calculations, Libby well-tried many items that archaeologists had antecedently dated. approximately of the items he tested included acacia wood from the first stepped pyramid tomb of Egyptian ruler Zoser(established rate 2700 B.C. Libby date 3979350 years), cypress wood 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 mom coffin from the Ptolemaic period in Egypt (established date 2280Libby 2190450 years), wheat and barley seeds (established date 5000 years old Libby date 5256230 years), and lastly, 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 prototype date, which dated too far back in history, his experimental dates were accurate within an acceptable molding of error. These sample tests, along with many others, endureed that his carbon-14 test dating method was scientifically dependable within an acceptable margin of error for objects already dated. Libby and whence continued his drill on dating objects for which no dates had been established.Scientists and scholars began to send him samples from all over the world to radiocarbon date. This included dating artifacts from the Dead Sea Scrolls, Pompeii, Stonehenge, and unsanded Mexico. One of his most significant results occurred when his colleagues dated glacial debris near Two Creeks, Wisconsin. His scientific work provided strong evidence that the last Ice historic period in North the States had covered t he land as recently as 11,000 BCE years ago, not 25,000 years ago as most geologists forwardly believed (Libby 1952105). All of these accomplishments and the inroads Libby made in dating the past employing carbon-14 dating earned him the Nobel Prize in 1960.Although radiocarbon dating methods harbor improved tremendously, Libbys boilersuit methodology is still utilized and accepted as a dating technique. It is based upon the fact that carbon-14 is a radioactive, unstable isotope of carbon-12 since its molecular composition has two more than(prenominal) neutrons than protons. Carbon-14 is made when cosmic rays enter the earths atmosphere and collide with nitrogen atoms. The unattached carbon neutrons then combine with nitrogen-14 atoms to become carbon-14 (Nitrogen-14 + neutron Carbon-14 + proton). As the resulting carbon-14 atoms sick down towards the earths surface they combine with oxygen to make carbon dioxide.This carbon dioxide includes the stable, common isotope carbon-1 2 and also tinyamounts of radioactive carbon-14. Both kinds of carbon, C-14 and C-12, be absorbed and used by plants and trees during the photosynthesis process and become part 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 atmosphere and the trace amount of carbon-14 in them starts to slowly decay back to nitrogen (Carbon-14 Nitrogen-14 + Beta ()).Beta particles be single electrons that are free from atoms and canalize a negative charge (DeYoung 200525). At the point of death, all organisms contain one atom of carbon-14 for every trillion atoms of carbon-12 (Poole 196125). Carbon dating requires determining 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 cont ent in the sample to determine its age taking into neb carbon-14s half-life and other calibration factors (DeYoung 200546-48).Since the amount of carbon-14 in each sample is miniscule, it is necessary to bring several clean samples of the uniform artifact being dated. It is imperative to avoid contamination of the artifacts as any carbon-14 found in the non-sample genuine, such as roots or other decaying remains which index be from a different time period, could significantly distort the results since the percentage of carbon-14 in a sample is minute (Hedman 200758). Therefore, scientists or archeologists generally stash away large samples be generate when they cleanse the sample, which includes purification and distillation processes, small amounts of matter tend to be removed.The trowels must be meticulously cleaned and the artifacts are packed in chemically neutral materials to ensure that the samples ratio of C-14 to C-12 remains the alike. The stratigraphy of where the s ample was taken must also be examined to ensure that the carbon sample office was not contaminated. In addition, scientists extract several samples in put in to perform similar test on the artifact to confirm the accuracy of the dates they calculate. In order to determine a samples age, scientists perform experimental trials to identify and count the number of carbon-14 atoms in the sample based on carbon-14s unique physical properties of big mass and radioactivity (Hedman 200758).Today, scientists manipulate two formulas to determine the age of an artifact. One is the formula t = (1/)ln (I0/I), where symbolizes the decay constant for carbon-14, I stands for the amount of carbon-14 in the at rest(predicate) matter, t represents time in years, and I0 is the carbon-14 in living matter (LAnnunziata 2007526). This formula calculates the time that has elapsed from the time of death of an organism. The second 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 given 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 ratio 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 production 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 radioactivity of carbon-14s unstable nuclei. They, as well 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 soak it in chemicals to confirm any contamination particles that remain on the artifact are gone prior to it being tested. The next step is to abstract the carbon-14 atoms from everything else in the wood. To do this, scientists place the wood in a heavy glass tube and then burn it. When this reaction occurs, the burning of the wood leaves very little ash and emits carbon dioxide, which is collected in a purification vacuum system. Once the gas 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 b y 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 can 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 silver Scintillation counting method. This was particularly popular during the 1960s.The Liquid Scintillation counting method converts a sample to carbon dioxide either 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). Once this process finishes, the benzene is driven off and collected under a vacuum to be count ed for carbon-14 content 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 high precision in dating. Advancement in technology has led to the deuce-ace method of radiocarbon dating, which is more precise than the other two methods. This process is accelerator mass spectrometry or AMS.This technique uses multiple stages of acceleration and ionization, as well as several magnets to separate the carbon-14 isotopes from all other 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 happen to decay. This makes this method very sensitive and can give accurate dating even if only one milligram of carbon is provided (Hedman 200760). The limit of carbon-14 detection using AMS is about 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 analyzed 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 about thirty specialized places throughout the world, and it is very expensive to test samples utilizing this method (Hedman 200760). Various scientists use radiocarbon dating as a device to measure ages of artifacts however, it is categorized under the Culture History theoretical school of thought in archaeology.Culture Historyarchaeologists focus their work on cultural processes and work to determine human behavior. In the field their focus is keened toward the distribution of artifacts that can define traits, which leads to defining cultures and changes over time. Carbon-14 dating falls under this theore tical 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 aid in defining a culture or changes in culture over time (shortman). One of the areas where carbon dating has been particularly useful is in stressful to date the evidence of human activity in the Americas.Prior to carbon-14 dating, most scientists believed the last Ice geezerhood ended about 25,000 years ago (Poole 196151). In 1950, ancient logs from spruce trees were found under glacial debris near Two Creeks, Wisconsin. Scientists were certain that these trees were crushed by the fourth Ice sequence. Pieces of this wood were sent to Libby for dating. Based on his tests, the last Ice Age had spread across the land as recently as 11,000 years ago This meant scientists had to restudy and revise previous dates of other natural events (Poole 196152-53). Another example of how carbon-14 dating helped was dating the evidence of humans c oming to the New World.This evidence revolves around 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 flint or volcanic render like obsidian that can be chipped away to form sharp edges. Clovis points have been found throughout the United States, and at several sites, these artifacts were found with the remains of mammoths. Carbon-14 dating of these Clovis points places 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 people in the Americas a great deal 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 Meadowcro ft 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 interrogatorysuggested the artifacts were 14,000 to 15,000 years old.This site also appears to be older than Clovis, which is surprising given the fact that 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 beds. It seems unlikely deciduous trees could survive the ice age yet the excavators counter this argument verbalise the area was sheltered which made the climate milder. Meadowcroft skeptics also suggested that the samples might be contaminated since the site is in the heart of coa l country.If any of the surrounding material (which no longer had carbon-14 in it since it had already decayed) was mixed 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 mixture of material from 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 ad dition, its accuracy is debated. virtually scientists question the validity of using 5,730 years as a half-life since this assumes nuclear half-lives have always 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 increased because of nuclear bombs and reactors. Artifacts from this era would be dated younger than they really are since they have a higher 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 adjust 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 calibrated to the tree ring dates.This has greatly improved the accuracy of this dating technique (Wheatley 200498). The earths 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 impart influence 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, t he 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, corns photosynthesis process causes it to have 2-3% higher carbon-14 fraction than shekels 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 corn (Hedman 200768-69). Despite these limitations, in my opinion, carbon-14 dating is an invaluable 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 dampen 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 discredit this dating technique because of some of its assumptions, however, refinements to this carbon dating process and collaboration with other dating techniques, such asdendrochronology, continue 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 Challenging 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. Chicago University of Chicago P, 2007. 49-95. H igham, Thomas. The 14C Method. Radiocarbob WEB-info. 9 Aug. 2002. 26 Sept. 2009 . LAnnunziata, Michael. Willard F. Libby. Radioactivity Introduction and History. 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