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== Limits of Carbon Dating ==
First, it hsd had not been proven scientifically whether the rate of decay of C-14 has remained constant over hundreds or thousands of years. Some scientists have suggested, based on experimental observations, that the laws of physics do change over time.<ref>"The idea that nature's laws change over time was proposed in the 1930s by one of the titans in the history of physics, Paul Dirac of England. According to Dirac's large numbers hypothesis, the force of gravity changed over time." See Keay Davidson, "Recent study forces scientists to rethink basic law of physics," San Francisco Chronicle[http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2005/05/09/MNG5LCLEU41.DTL]</ref>
Second, estimating the age of material using carbon dating assumes that the ratio of C-14 to C-12 was the same in the past as today, which is also impossible to prove scientifically. "[T]he proportions of C-14 in the atmosphere in historic times is unknown. The C-14:C-12 atmospheric ratio is known to vary over time and it is not at all certain that the curve is 'well behaved.'"<ref>Nondestructive Testing (NDT) Resource Center, "Uncertainty in Carbon Dating"[http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/carbondating.htm]</ref>
