School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland.
Proc Natl Acad Sci U S A. 2010 Dec 28;107(52):22448-53. doi: 10.1073/pnas.1011974107. Epub 2010 Dec 13.
Atmospheric oxygen (O(2)) is estimated to have varied greatly throughout Earth's history and has been capable of influencing wildfire activity wherever fuel and ignition sources were present. Fires consume huge quantities of biomass in all ecosystems and play an important role in biogeochemical cycles. This means that understanding the influence of O(2) on past fire activity has far-reaching consequences for the evolution of life and Earth's biodiversity over geological timescales. We have used a strong electrical ignition source to ignite smoldering fires, and we measured their self-sustaining propagation in atmospheres of different oxygen concentrations. These data have been used to build a model that we use to estimate the baseline intrinsic flammability of Earth's ecosystems according to variations in O(2) over the past 350 million years (Ma). Our aim is to highlight times in Earth's history when fire has been capable of influencing the Earth system. We reveal that fire activity would be greatly suppressed below 18.5% O(2), entirely switched off below 16% O(2), and rapidly enhanced between 19-22% O(2). We show that fire activity and, therefore, its influence on the Earth system would have been high during the Carboniferous (350-300 Ma) and Cretaceous (145-65 Ma) periods; intermediate in the Permian (299-251 Ma), Late Triassic (285-201 Ma), and Jurassic (201-145 Ma) periods; and surprisingly low to lacking in the Early-Middle Triassic period between 250-240 Ma. These baseline variations in Earth's flammability must be factored into our understanding of past vegetation, biodiversity, evolution, and biogeochemical cycles.
大气中的氧气（O(2)）据估计在地球历史上发生了巨大的变化，并且在有燃料和点火源的地方都能够影响野火活动。火灾在所有生态系统中消耗大量的生物质，并在生物地球化学循环中发挥重要作用。这意味着，了解氧气对过去火灾活动的影响对于生命在地质时间尺度上的演化以及地球生物多样性具有深远的意义。我们使用强大的电点火源点燃闷烧火灾，并测量它们在不同氧气浓度的大气中的自我维持传播。这些数据被用来构建一个模型，我们用它来根据过去 3.5 亿年来氧气的变化来估计地球生态系统的基线固有可燃性。我们的目的是强调地球历史上火灾能够影响地球系统的时期。我们揭示，在氧气浓度低于 18.5%的情况下，火灾活动将大大受到抑制，在氧气浓度低于 16%的情况下完全熄灭，而在氧气浓度为 19-22%之间则迅速增强。我们表明，火灾活动以及因此其对地球系统的影响在石炭纪（3.5 亿至 3 亿年前）和白垩纪（1.45 亿至 6500 万年前）期间将很高；在二叠纪（2.99 亿至 2.51 亿年前）、晚三叠纪（2.85 亿至 2.01 亿年前）和侏罗纪（2.01 亿至 1.45 亿年前）期间处于中等水平；而在早-中三叠纪（2.5 亿至 2.4 亿年前）期间则出人意料地低或缺乏。这些地球可燃性的基线变化必须被纳入我们对过去植被、生物多样性、进化和生物地球化学循环的理解中。
