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Carbon dating has been the focus of controversy since it’s discovery, but is indeed valid for determining the age of ancient carbon containing substances. There are complications, however, with carbon dating which must be addressed to assure accuracy (Schell, 1967; Stuiver, 1967; Suess, 1967; Morris, 1978; Coleman, 1991; Lepper, 1992; Whitelaw, 1993; Morris, 1998). First of all, it is essential to understand that Carbon-14 (C-14) can only be used with geologically "young" specimens because of it’s relatively short half-life of 5,730 years (Coleman, 1991; Hamblin, 1992; Lepper, 1992; Whitelaw, 1993). There are other problems with cabon dating, such as a discrepancy in the atmospheric ratio of carbon-14 vs. carbon-12 (Whitelaw, 1993). The specific production rate (SPR) of carbon-14 in the Earth’s atmosphere is greater than the specific decay rate (SDR) (Stuiver, 1967; Brown, 1993; Whitelaw, 1993; Morris, 1998). This shows, barring a ‘young Earth’ scenario, that the C-14 production in the atmosphere has not been constant throughout Earth's existence and has therefore lead to variations of C-14 in organic deposits, depending upon carbon conditions at the time (Schell, 1967; Stuiver, 1967; Suess, 1967; Whitelaw, 1993). Another potential problem with carbon dating is contamination of target samples from modern carbon sources (Coleman, 1991; Lepper, 1992; Brown, 1993; Whitelaw, 1993). These complications are the primary focus of debate aimed to discredit C-14 dating, and if not taken into account during the calibration of the dating process, the validity of carbon dating is indeed unreliable (Suess, 1967; Brown, 1993; Whitelaw, 1993).|
First of all, to avoid confusion, it is necessary to understand that carbon dating can only be use to date geologically young, 35k - 50k years, carbon containing substances (Lepper, 1992; Whitelaw, 1993). Having said this the next critical point to understand is the inconsistency of atmospheric C-14 levels throughout Earth’s history. Carbon-14 is produced primarily by solar radiation in Earth’s upper atmosphere (Morris, 1978). This radiation activity converts nitrogen-14, the most plentiful atmospheric gas, to carbon-14 (Morris, 1978). The C-14 then begins a slow decay process back to N-14 with a half-life of 5,730 years (Hamblin, 1992). If this radiation system were left unaltered the ratio of production to decay would eventually reach a state of equilibrium (Morris, 1978). The current atmospheric levels of radioactive carbon, however, are not in equalibrium (Schell, 1967; Stuiver, 1967; Suess, 1967; Morris, 1978; Whitelaw, 1993; Morris, 1998), but are in fact out of balance. The SPR is approximately 18% greater than the SDR (Whitelaw, 1993). In addition to the modern imbalance there has also been a slow but steady decrease in the amount of atmospheric C-14 since about 10,000 BP (before present) (Schell, 1967). This decrease was discovered by correlating C-14 proportions in objects of known historical age, tree rings and artifacts tied to specific historical events (Suess, 1967). There are many theories and speculations as to why the atmospheric C-14 imbalance exists. Creationists, for example, see it as evidence that the Earth is actually younger than geologists believe. This claim is based on the idea that C-14 production has not had sufficient time to reach an equilibrium since the world came to be (Morris, 1978; Lepper, 1992; Whitelaw, 1993; Morris, 1998). Most scientists, however, believe that the C-14 production system experiences fluctuations and this leads to the imbalance (Schell, 1967; Brown, 1993). Another explanation of the imbalance is the amount of cosmic radiation, the primary producer of C-14, fluctuates because of temporary conditions such as solar flares or solar wind (Schell, 1967; Brown, 1993). A decrease in the Earth’s geomagnetic field is also thought to be a possible contributor to C-14 production rates because the magnetic field influences the amount of cosmic radiation penetrating the atmosphere (Schell, 1967; Brown, 1993). There is also a theory that points to the recent ice age as a suspect in the C-14 imbalance mystery. This theory suggests that the ocean, because of the increase in temperature and volume at the melting of the last great glaciers, "sucked up" a lot of the atmospheric carbon (Suiver, 1967). If this is the case then the C-14 producing system simply has not since established equilibrium (Stuiver, 1967). A final theory, based on the attempts to bring science and religion into harmony, is that of an ancient "vapor canopy" (Whitelaw, 1993). This controversial theory states that before "Noah’s flood" there was more water vapor suspended in the atmosphere (Whitelaw, 1993). This "vapor canopy" would have shielded the Earth from cosmic radiation and thereby hindered the production of C-14 (Whitelaw, 1993). If this is the case then C-14, as in the ice age theory, is still building up since then and has not yet reached equilibrium (Whitelaw, 1993).
The other major factor which can invalidate carbon dating is contamination of subject samples. The ratio of C-14 to C-12 is only 0.03% (Libby, 1969), and because the level of radioactive carbon in any given sample is so small, especially when allotting time for exponential half-life decay, the smallest quantity of modern carbon contamination can severely skew dating results (Brown, 1993). Therefore it is of utmost importance to avoid using contaminated samples for carbon dating.
Samples may be contaminated in several ways. First, the collection site may contaminate samples even before they are considered for dating purposes (Coleman, 1991; Lepper, 1992; Brown, 1993; Whitelaw, 1993). For example, if the collection site is "wet," whether, swampy, near stream or alluvial systems, below the water table (including seasonal fluctuation of water tables), etc... it is possible for carbon dissolved in the water to transfer into the samples (Coleman, 1991). Tree roots also contaminate samples as any roots mixed in with a sample to be dated would contain modern carbon and alter the results of a C-14 test (Coleman, 1991). There is also a danger of contamination of samples exchanging carbon dioxide directly with the atmosphere (Coleman, 1991). Bones and shells, because of their naturally low carbon content, buried under anaerobic conditions (ex. bog) will often absorb carbon dioxide when exposed to the air (Coleman, 1991). There also exists danger with dating lake and fluvial sediments. If a lake, for example, contains carbon from an ancient source such as a old peat bog, limestone, or other deposit it’s sediments will not accurately reflect historical atmospheric C-14 levels (Coleman, 1991). Finally, there is the problem with "apparent age." Deep sea ocean currents travel along the ocean bottom unexposed to air for centuries at a time and can be depleted of C-14 by deep oceanic systems such as biological processes or chemical precipitation (Hamblin, 1992). Sediments and organisms which derive their carbon from such ocean water will reflect an "apparent age" not an actual age (Coleman, 1991).
Carbon-14 dating has considerable problems which can alter it’s efficiency. There are methods, however, for avoiding its downfalls. The first obstacle to overcome in C-14 dating is the determination of atmospheric C-14 levels at the time of a given sample’s formation (Whitelaw, 1993). Carbon dating techniques can be calibrated using items of known historical age such as tree rings and historical artifacts (Suess, 1967). This is done by measuring current C-14 levels in a given sample and then calculating the initial carbon ratio based on the samples known age (Suess, 1967). This calibration process determines environmental conditions of a specific past time period (Suess, 1967; Brown, 1993; Morris, 1998). Without this historical environmental knowledge any attempt at carbon dating would be based on assumption (Stuiver, 1967; Morris, 1978; Morris, 1998). Therefore the accuracy of C-14 dating decreases with ages greater than 4000 BP. This decrease occurs because calibration ability is lost due to a lack of historical records (Brown, 1993).
Aside from ancient environmental conditions the other danger in C-14 dating is contamination with non-contemporary carbon sources (Lepper, 1992) Therefore, proper decontamination of samples is essential for accurate carbon dating and the best way to limit contamination is to avoid it. Samples should be collected from uncontaminated sites where there has been no exchange of carbon from non-contemporary sources (Brown, 1993). It is also a good idea to use samples that do not readily exchange carbon dioxide with the air such as wood, charcoal, and peat (Coleman, 1991). If contamination prevention is unavoidable, however, decontamination of samples is possible by both mechanical and chemical means (Coleman, 1991). Mechanical decontamination involves procedures such as removal of roots and other foreign material from the sample (Coleman, 1991). Chemical decontamination removes carbonates through treatment with phosphoric or hydrochloric acids (Coleman, 1991).
Carbon dating is a valid and useful tool for determining a carbon containing item’s age. However, the use of radiocarbon can only be applied to objects less than 50,000 years old and preferably not much older than 4000 BP, due to a loss in calibration ability (Brown, 1993). Radiocarbon techniques can also suffer inaccuracies if proper decontamination procedures are not followed (Lepper, 1992; Brown, 1993). With proper care, carbon dating can be a powerful tool to the scientific community.