While radiocarbon dates are flung around when reporting very recent geological events, often very little thought is given to what they represent. Unlike other radiometric dating methods, the amount of carbon 14 (~(14) C) present at the start of the process is not constant over time. In living tissue carbon dioxide is exchanged with the atmosphere where varying amounts of fresh ~(14) C are generated and via the carbon cycle remain in global equilibrium. Modern carbon only contains roughly one part in a million, million (1.2 X 10 ~(-12)) of radioactive isotope ~ (14) C compared with ~ (13) C (approx 1 per cent) and ~ (12) C (approx 99 per cent). Cosmic rays generate neutrons in the upper atmosphere that collide with nitrogen atoms (~(14) N) to produce (14) C which then forms carbon dioxide. This interacts with the biosphere so that, when a plant or animal dies, the clock starts and the ~(14) C it contains starts to decay back into ~(14) N at a constant rate. On top of this, atmospheric nuclear explosions between 1945 and the 1970s generated an additional ~(14) C spike, while the burning of fossil fuels have diluted ~(14) C levels by adding ancient carbon to the atmosphere.
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机译：虽然在报告非常近期的地质事件时会放出放射性碳的日期，但通常很少考虑它们的含义。与其他辐射测年方法不同，该过程开始时存在的碳14（〜（14）C）的量随时间变化不是恒定的。在活组织中，二氧化碳与大气交换，在大气中产生不同数量的新鲜〜（14）C，并通过碳循环保持整体平衡。与（13）C（约1％）和〜（12）C（〜（13）C（约1％））相比，现代碳仅包含一百万，百万（1.2 X 10〜（-12））放射性同位素〜（14）C中的大约一部分。约99％）。宇宙射线在高层大气中产生中子，该中子与氮原子（〜（14）N）发生碰撞，从而产生（14）C，然后形成二氧化碳。它与生物圈相互作用，因此，当植物或动物死亡时，时钟开始，并且其中包含的〜（14）C开始以恒定速率衰减回到〜（14）N。最重要的是，1945年至1970年代之间的大气核爆炸产生了额外的〜（14）C峰值，而化石燃料的燃烧通过向大气中添加古老的碳而稀释了〜（14）C的水平。
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