Science. 1988 Mar 18;239(4846):1406-9. doi: 10.1126/science.239.4846.1406.
Gases trapped in Miocene to Upper Cretaceous amber were released by gently crushing the amber under vacuum and were analyzed by quadrupole mass spectrometry. After discounting the possibility that the major gases N(2), O(2), and CO(2) underwent appreciable diffusion and diagenetic exchange with their surroundings or reaction with the amber, it has been concluded that in primary bubbles (gas released during initial breakage) these gases represent mainly original ancient air modified by the aerobic respiration of microorganisms. Values of N(2)/(CO(2) + O(2)) for each time period give consistent results despite varying O(2)/CO(2) ratios that presumably were due to varying degrees of respiration. This allows calculation of original oxygen concentrations, which, on the basis of these preliminary results, appear to have changed from greater than 30 percent O(2) during one part of the Late Cretaceous (between 75 and 95 million years ago) to 21 percent during the Eocene-Oligocene and for present-day samples, with possibly lower values during the Oligocene-Early Miocene. Variable O(2) levels over time in general confirm theoretical isotope-mass balance calculations and suggest that the atmosphere has evolved over Phanerozoic time.
被困在中新世到上白垩纪琥珀中的气体在真空中轻轻粉碎琥珀后被释放出来，并通过四极杆质谱仪进行分析。在排除主要气体 N(2)、O(2)和 CO(2)与周围环境发生明显扩散和成岩交换或与琥珀发生反应的可能性之后，可以得出结论，在原始气泡（在初始破裂期间释放的气体）中，这些气体主要代表原始古代空气，受微生物需氧呼吸的影响。尽管 O(2)/CO(2)比值不同，这可能是由于呼吸程度不同，但每个时间段的 N(2)/(CO(2)+O(2))值给出的结果一致。这允许计算原始氧浓度，根据这些初步结果，在白垩纪晚期（约 7500 万至 9500 万年前）的一部分时期，原始氧浓度似乎大于 30%，在始新世-渐新世和现在的样本中，可能在渐新世-早中新世时期更低，随着时间的推移，氧气水平的变化总体上证实了理论同位素质量平衡计算，并表明大气在显生宙期间发生了演变。
