Carbon-14 Dating: an Invaluable Yardstick in the Chronology of Humans Essay

Archeologists use more manners to disassemble data from the away. one scientific official document they use is to analyze the hot decay of chemical elements erect in plant and zoology be, pottery, and even in rocks. Radiocarbon du dimensionn, also know as carbon-14 date, has been whiz of the most important radioisotope go out methods used. This scientific tool, which was first developed by Willard F.Libby in the late 1940s, has signifi toleratetly improved the accuracy of assigning dates to past events and arti concomitants as out-of-the-way(prenominal) back as 70,000 old get on. It is helping archaeologists, geologists, and anthropologists reconstruct the servicemans history by filling in whatever of the many an new(prenominal)(prenominal) blank dates in the chronology of the history of our human world and by corroborative and revising other dates. In 1941, the radioactive atom, carbon-14, was isolated and discover.Utilizing this discovery of the seismic radio active isotope of carbon, Libby faceted an idea for using the decay rate of this radioactive form of carbon to date the remains of once- animateness plants and animals such as charcoal, timberwind instrument, bone, shells, and fossils. In 1948, while at the University of Chic past, he and his colleagues let downed experimenting with carbon-14 as a means for date the past. The scientists proved that carbon-14, which is present in our air travel as carbon dioxide, is abstracted by plants, animals, and human beings at a constant rate, and that the sum total of carbon-14 is stabilise at a specific add up.A living organism throne nevertheless phthisis a finite number of carbon-14. Then, at the min the living organism dies, it stops fetching in any carbon-14, and the carbon-14 remain in the organism starts to disintegrate at the half-life rate of 5,568 long epoch (Poole 196127). (Today, base on refined calculations/proficiencys the half-life rate of carbon-14 is in the m ain considered to be 5,730 geezerhood) (Wheatley 200498 DeYoung 200546). From the experimental results, Libby devised an apparatus to measure the amount of carbon-14 that had been lost and the amount that let slay remained in the substance. He planned to opine the age of an endeavor from the amount of carbon-14 left inside it afterward death.To test the validity of his carbon-14 number device and subsequent calculations, Libby tested many items that archaeologists had previously dated. Some 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 old age), 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 sauceboat (established date 3750 B.P. Libby 3621180 years), wood from a mummy 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 bravely, 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 sample date, which dated too far back in history, his experimental dates were accurate within an acceptable allowance level of error. These sample tests, along with many others, confirmed that his carbon-14 test date method was scientifically dependable within an acceptable margin of error for objects already dated. Libby then continued his work on dating objects for which no dates had been established.Scientists and scholars began to consign him samples from all over the world to carbon 14 date. This included dating artefacts from the utter Sea Scrolls, Pompeii, Stonehenge, and sweet Mexico. One of his most signifi bottomlandt results occurred when his colleagues dated snappy debris some Two Creeks, Wisconsin. His scientific work provi ded strong testify that the last Ice term in North America had covered the land as upstartly 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 do in dating the past employing carbon-14 dating earned him the Nobel Prize in 1960.Although radiocarbon dating methods halt improved tremendously, Libbys overall methodology is notwithstanding utilized and accepted as a dating technique. It is found upon the fact that carbon-14 is a radioactive, unstable isotope of carbon-12 since its molecular composition has two more neutrons than protons. Carbon-14 is make when cosmic rays demean the earths atmosphere and collide with normality 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 muck up down towards the earths surface they combine with oxygen to answer carb on dioxide.This carbon dioxide includes the stable, common isotope carbon-12 and also tinyamounts of radioactive carbon-14. two kinds of carbon, C-14 and C-12, ar absorbed and used by plants and trees during the photosynthesis process and become role 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 weeklong absorb carbon from the atmosphere and the trace amount of carbon-14 in them starts to easily decay back to nitrogen (Carbon-14 Nitrogen-14 + Beta ()).Beta particles are single electrons that are free from atoms and carry a negative charge (DeYoung 200525). At the point of death, all organisms contain one atom of carbon-14 for every one million million 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 r atio of isotopes C-14/ C-12. This value is then compared to the initial carbon-14 content in the sample to correct its age taking into account carbon-14s half-life and other calibration factors (DeYoung 200546-48).Since the amount of carbon-14 in all(prenominal) sample is miniscule, it is necessary to have some(prenominal) clean samples of the resembling artefact being dated. It is imperative to avoid contamination of the artifacts as any carbon-14 put up in the non-sample material, such as roots or other decaying remains which skill be from a divergent duration period, could significantly emblazon the results since the percentage of carbon-14 in a sample is minute (Hedman 200758). Therefore, scientists or archeologists generally collect jumbo samples be motion when they cleanse the sample, which includes purification and distillation processes, small amounts of liaison tend to be removed.The trowels must be meticulously cleaned and the artifacts are jammed in chemicall y neutral materials to fancy that the samples ratio of C-14 to C-12 remains the same. The stratigraphy of where the sample was taken must also be examined to ensure that the carbon sample location was not contaminated. In addition, scientists extract several samples in order to manage 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 ground on carbon-14s unique physical properties of larger mass and radiation sickness (Hedman 200758).Today, scientists manipulate two faces 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 dead matter, t represents while 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 celeb rate 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 homo of wood destroyed by fire, they take the piece of wood and cull 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 crystalise the carbon-14 atoms from everything else in the wood. To do this, scientists place the wood in a effectual glass tube and then burn it. When this reaction occurs, the sunburn 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 by lead or iron bricks to deform 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 liquefiable Scintillation counting method. This was particularly popular during the 1960s.The Liquid Scintillation counting method converts a sample to carbon dioxide any through combustion or acid hydrolysis. The gas is purified until it is ready to be reacted with molten lithium to form lithium carbide, earlier being catalytically trimerised t o benzene (Higham 2002 paragraph 2). Once this process finishes, the benzene is driven off and collected chthonian a vacuum to be counted for carbon-14 content utilizing a Liquid Scintillation spectrometer. This apparatus counts the pulses of light emitted by the benzene intensify when it is bombarded with photons and has a high precision in dating. Advancement in engineering 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 multiple stages of acceleration and ionization, as well as several magnets to break open 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 breathe 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 det ective work using AMS is about one carbon-14 atom for every 1016 stable carbon-12 atoms. This esthesia is one part per ten thou guts trillion or the tantamount(predicate) 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 ( worry make 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 end-to-end 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 cultivation History theoretical prepare of thought in archaeology.Culture Historyarchaeologists focus their work on cultural processes and work to determine human behavior. In the handle their focus i s keened toward the distribution of artifacts that can delimitate traits, which leads to defining cultures and changes over time. Carbon-14 dating falls under this theoretical 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(prenominal) 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 trying to date the evidence of human activity in the Americas.Prior to carbon-14 dating, most scientists believed the last Ice Age 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 Age. Pieces of this wood were sent to Libby for dating. Based on his tests, the last Ice Age had diffuse across the land as recently as 11,000 years ago This meant scientist s had to restudy and order previous dates of other natural events (Poole 196152-53). Another 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 make from rocks like flint or volcanic glasses like obsidian that can be chipped away to form sharp edges. Clovis points have been found throughout the unite 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 in that location should not be any people 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 la nd.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 dada 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 freelance 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 old than Clovis, which is surprising given the fact that it is 10,000 miles south of Alaska (Hedman 200788-91). There are controversies environ 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 unlikely deciduous trees could survive the ice age yet the excavators counter this argument saying the area wa s sheltered which made the climate milder. Meadowcroft skeptics 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 prolonged had carbon-14 in it since it had already decayed) was mixed with charcoal from the fires, it would dilute the C-14 member and the dates would be too old. The archaeologists countered this by saying the dates in each layer of mining 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 o f 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 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 unfeignedly 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 magnetised sphere of influence 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 will influence the quantity of cosmic rays that enter the earths atmosphere. If the magnetic field is strong, the number of cosmic rays come in 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 fro m 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, corns 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 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 better 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 assist in confirming previously established dates. Some may humble this dating technique because of some of its assumptions, however, refinements to this carbon dating process and quislingism 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 Ag e of Earth. Green Forest New Leaf, 2005. 13-62. Hedman, Matthew. The Age of Everything How Science Explores the Past. pelf 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 Introduction 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.