但是，有一个问题。大气中的碳随着地球磁场强度和太阳活动而波动。你必须知道在有机体死亡时大气中的碳含量（放射性碳“储层”）是什么样的，以便能够计算自有机体死亡以来已经过了多少时间。你需要的是一个标尺，一个可靠的水库地图：换句话说，你可以安全地确定日期的有机物体集，测量其C14含量，从而建立给定年份的基线水库。幸运的是，我们确实有一个有机物体，每年跟踪大气中的碳：树木年轮。树木在它们的生长环中保持碳14平衡 – 树木每年都会生存一个环。虽然我们没有任何有5万年历史的树木，但我们确实有重叠的树木戒指，可以追溯到12，594年。换句话说，我们有一个非常可靠的方法来校准我们这个星球过去最近12，594年的原始放射性碳日期。但在此之前，只有零碎的数据可供使用，因此很难明确确定13，000年以前的任何数据。可靠的估计是可能的，但具有大的+/-因子。正如你可能想象的那样，科学家们一直试图发现其他有机物，这些有机物可以在利比发现之后稳定地安排。其他检查的有机数据集包括varves（沉积岩中的层，每年铺设，包含有机物质，深海珊瑚，洞穴（洞穴沉积物）和火山喷发岩;但这些方法都存在问题。 varves有可能包括旧的土壤碳，并且海洋珊瑚中C14的波动量仍有尚未解决的问题。
However, there is a problem. The carbon in the atmosphere fluctuates with the strength of the Earth’s magnetic field and solar activity. You must know what the carbon content of the atmosphere (radiocarbon “reservoir”) is when the organism dies, so that you can calculate how much time has passed since the death of the organism. What you need is a ruler, a reliable reservoir map: in other words, you can safely determine the date set of organic objects and measure their C14 content to establish a baseline reservoir for a given year. Fortunately, we do have an organic object that tracks the carbon in the atmosphere every year: the tree rings. Trees maintain a balance of carbon 14 in their growth rings – trees live a ring every year. Although we don’t have any trees with 50,000 years of history, we do have overlapping tree rings that date back to 12,594. In other words, we have a very reliable way to calibrate the date of our planet’s original radioactive carbon in the last 12,594 years. But before that, only piecemeal data was available, so it was difficult to clearly identify any data before 13,000 years. A reliable estimate is possible, but with a large +/- factor. As you might imagine, scientists have been trying to discover other organics that can be steadily arranged after Libby is discovered. Other organic data sets for inspection include varves (layers in sedimentary rocks, laid annually, containing organic matter, deep-sea corals, caves (cave sediments) and volcanic eruptions; but these methods are problematic. Varves may include old soil carbon And there are still unresolved problems with the fluctuations of C14 in marine corals.