英國科學(xué)家日前否定了一種解釋地球上最大規(guī)模的物種滅絕事件的重要假說,。在那次滅絕事件中,，９５％的海洋物種以及７０％的陸地物種被毀滅,。
那次災(zāi)難被稱為“大滅絕”,，發(fā)生于約２．５億年前的二疊紀(jì)末期,。在歷史長河中,，該事件也許已經(jīng)逐步為人們所了解,，有越來越多的線索證明了其嚴(yán)重程度,，包括在全球范圍發(fā)現(xiàn)的難以解釋的、已石化的,、產(chǎn)生了突變的植物種子,。盡管如此，是什么原因?qū)е铝嗽撌录胁磺宄?/p>
據(jù)法新社報(bào)道,，被英國研究人員否定的理論認(rèn)為,，海洋變得缺氧，富含硫化物,，致使海洋生物滅絕,。
硫化物煙霧從海面升騰而起，在頻繁的火山活動釋放的副產(chǎn)品甲烷的協(xié)助下,，破壞了臭氧層,。臭氧層相當(dāng)于大氣平流層中的盾牌，可以過濾掉陽光中紫外線Ｂ的輻射,。
這種理論認(rèn)為,，在地面上生物遭到了徹底毀滅。生物因硫化物累積到有毒程度而中毒,，其ＤＮＡ則因陽光輻射而被完全破壞,。
由英格蘭北部設(shè)菲爾德大學(xué)的戴維·比爾林帶領(lǐng)的研究小組創(chuàng)建了一種大氣化學(xué)研究二維計(jì)算機(jī)模型，來檢驗(yàn)這種觀點(diǎn),。
據(jù)他們的計(jì)算結(jié)果,，赤道地區(qū)的低氣壓會起到氧化緩沖作用，阻止硫化物嚴(yán)重破壞臭氧層,。他們在《自然地球科學(xué)》雜志上報(bào)告說：“這些毒氣似乎不太可能是偶然發(fā)生的地球物種滅絕的原因,。”
關(guān)于“大滅絕”還有其他多種理論，包括小行星造成的一次或是一系列影響,。這與人們認(rèn)為的６２００萬年前造成恐龍滅絕的事件相似,。
生物谷推薦原始出處：
（Nature Geoscience），doi:10.1038/ngeo154,，Michael B. Harfoot, John A. Pyle & David J. Beerling）
End-Permian ozone shield unaffected by oceanic hydrogen sulphide and methane releases
Michael B. Harfoot1, John A. Pyle1,2 & David J. Beerling3
Earth experienced repeated episodes of widespread surface and deep-ocean anoxia with a significant accumulation of sulphide-rich waters over the past two billion years1, 2. The resulting massive releases of hydrogen sulphide from the oceans, together with methane from the geosphere, have been suggested as a cause for mass extinctions through destruction of the ozone shield and a lethal accumulation of hydrogen sulphide at the surface1, 2, 3, 4. Here, we use a two-dimensional atmospheric chemistry-transport model5, 6, 7 with representative climate8 and atmospheric composition9 to simulate the effect of large hydrogen sulphide and methane releases at the time of the end-Permian mass extinction 251 million years ago. In our simulations, the integrity of the stratospheric ozone shield is maintained for oceanic hydrogen sulphide releases up to 15,000 Tg S yr-1, a limit far exceeding the threshold for ozone collapse identified previously1 (2,000–4,000 Tg S yr-1). Scenarios of simultaneous hydrogen sulphide and methane injections also failed to significantly deplete the Earth's ozone shield, and generated non-lethal hydrogen sulphide concentrations (1–2 p.p.m.) at the surface. In our two-dimensional model simulations, the high photolysis environment in the tropics maintains the oxidizing capacity of the tropical troposphere, with high local hydroxyl radical concentrations, and greatly diminishes hydrogen sulphide entry into the stratosphere. We suggest that given current constraints on possible hydrogen sulphide and methane releases from anoxic oceans, and the geosphere, over the past 0.5 billion years, these gases seem unlikely to be the cause of coincident terrestrial biotic mass extinctions.
