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G. Contamination poses a further challenge. Any addition of carbon of a different age distorts the measured date. Modern carbon contamination - from handling, conservation chemicals, or groundwater infiltration - makes a sample appear younger than it truly is; the effect is particularly severe for very old samples, where even a 1% contamination with modern carbon can shift a 34,000-year-old sample's apparent age by 4,000 years. Conversely, contamination with "dead" carbon (carbon containing no carbon-14, such as limestone carbonate) makes samples appear older. Rigorous chemical pretreatment protocols, including ultrafiltration of bone collagen and acid-base-acid washing of charcoal, are employed to remove contaminants, but complete elimination is not always achievable. H. The shape of the calibration curve itself introduces a subtler limitation. Where the curve is steep and monotonic, a given radiocarbon age maps to a narrow, well-defined calendar range. Where the curve flattens - forming what are called "plateaus" - a wide range of calendar dates may correspond to nearly identical radiocarbon ages, making precise dating impossible. In such cases, even the most accurate AMS measurement cannot resolve the calendar age beyond a range of several centuries. One technique that mitigates this problem is "wiggle matching," in which a series of radiocarbon dates from a known stratigraphic sequence (such as successive tree rings or archaeological layers) is matched against the wiggles of the calibration curve, yielding a more precise chronological placement than any single date could provide. I. In recent years, radiocarbon dating has found applications far beyond archaeology and palaeontology. In forensic science, the bomb-pulse carbon-14 signal has been used to determine the year of birth or death of unidentified human remains by analysing eye-lens crystallines and tooth enamel - tissues that, once formed, do not undergo carbon turnover. In environmental science, carbon-14 measurements help distinguish fossil-fuel-derived carbon from biogenic carbon in atmospheric particulate matter, contributing to our understanding of anthropogenic climate change. The continued refinement of AMS technology, including the development of compact accelerator systems and improved graphitisation techniques, promises to extend the method's reach further still - both backward in time and into ever smaller and more precious samples.
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