古代岩石顯示地球如何從大滅絕事件中復原

Ancient rocks reveal how Earth recovered from mass extinction

古代岩石顯示地球如何從大滅絕事件中復原

Scientists have shed light on why life on Earth took millions of years to recover from the greatest mass extinction of all time.

科學家揭露地球上的生命為何花了數百萬年才從史上最慘重的大滅絕中復原。

The study provides fresh insight into how Earth's oceans became starved of oxygen in the wake of the event 252 million years ago, delaying the recovery of life by five million years.

這項研究提出的最新觀點認為在2億5200萬年前的滅絕事件之後，海洋變得十分缺乏氧氣而將生物的復甦時間延長至5百萬年之久。

Findings from the study are helping scientists to better understand how environmental change can have disastrous consequences for life on Earth.

這項研究的發現有助於科學家更加了解環境變遷如何對地球上的生物造成災難性的影響。

The Permian-Triassic Boundary extinction wiped out more than 90 per cent of marine life and around two thirds of animals living on land. During the recovery period, Earth's oceans became starved of oxygen -- conditions known as anoxia.

發生在二疊紀與三疊紀之際的大滅絕事件殲滅了超過90%的海洋生物，陸上生物也有將近2/3就此消失。在接下來的復原階段，地球海洋的氧氣變得十分不足，這種情況稱作缺氧(anoxia)。

Previous research suggested the mass extinction and delayed recovery were linked to the presence of anoxic waters that also contained high levels of harmful compounds known as sulphides.

過往研究認為大滅絕事件以及耗時許久的復原期跟海水處於缺氧狀態，且同時含有高濃度的有毒化學物質—硫化物之間有密切關聯。

However, researchers say anoxic conditions at the time were more complex, and that this toxic, sulphide-rich state was not present throughout all the world's oceans.

然而，研究人員聲稱當時的缺氧狀況實際上還要更加複雜，而全世界的海洋也不盡然都處於具備毒性且富含硫化物的狀態。

The team, led by researchers at the University of Edinburgh, used precise chemical techniques to analyse rocks unearthed in Oman that were formed in an ancient ocean around the time of the extinction.

由愛丁堡大學的研究人員率領的團隊，利用精確的化學技術來分析從阿曼挖掘出來的岩石。它們形成於大滅絕發生時的古代海洋當中。

Data from six sampling sites, spanning shallow regions to the deeper ocean, reveal that while the water was lacking in oxygen, toxic sulphide was not present. Instead, the waters were rich in iron.

從淺海地區分佈至深海的六個採樣地點得到的數據顯示，雖然當時海洋缺乏氧氣，但卻沒有毒性硫化物。反之，這些水體富含鐵質。

The finding suggests that iron-rich, low oxygen waters were a major cause of the delayed recovery of marine life following the mass extinction.

這項發現認為大滅絕之後海洋生命經過許久才恢復，主因便是海洋處於富含鐵質且缺乏氧氣的狀態。

The study also shows how oxygen levels varied at different depths in the ocean. While low oxygen levels were present at some depths and restricted the recovery of marine life, shallower waters contained oxygen for short periods, briefly supporting diverse forms of life.

研究也顯示出海洋中的氧氣濃度會隨著深度而變化。雖然在某些深度低氧濃度限制了海洋生命復甦，但淺海卻有一小段擁有氧氣的時期，而能夠暫時養活不同種類的海洋生物。

The precise cause of the long recovery period remains unclear, but increased run-off from erosion of rocks on land -- caused by high global temperatures -- likely triggered anoxic conditions in the oceans, researchers say.

如此長的恢復期確切成因仍然不明，但研究人員認為全球溫度提高造成有更多的陸上岩石侵蝕產物進入海洋，是海洋變成缺氧狀態的可能成因。

The study, published in the journal Nature Communications, was funded by the Natural Environment Research Council and the International Centre for Carbonate Reservoirs. The work is a contribution to the UNESCO International Geoscience Programme. It was carried out in collaboration with the Universities of Leeds, Gratz, Bremen and Vienna University.

刊登於期刊《自然通訊》(Nature Communications)上的這篇研究由自然環境委員會及國際碳酸鹽儲層中心資助，且為聯合國文教組織國際地質學計畫的一部分。共同合作機構包括了里茲大學、格拉茨大學、不萊梅大學和維也納大學

Dr Matthew Clarkson, of the University of Edinburgh's School of GeoSciences, who led the study, said: "We knew that lack of oxygen in the oceans played a key role in the extinction and recovery processes, but we are still discovering how exactly it was involved. Our findings about the chemistry of the ocean at the time provide us with a clearer picture of how this complex process delayed the recovery of life for so long."

愛丁堡大學地質科學系的 Matthew Clarkson博士主持了此篇研究。他說：「我們雖已知道在滅絕事件及後續的回復過程中，海洋缺氧扮演了關鍵腳色，但我們仍在尋找它在其中的確切作用。這項關於當時海洋化學性質的發現，呈現出一幅清晰的圖像讓我們得以了解這些複雜的作用如何大幅延遲海洋生命從災難中復甦回來。」

Professor Simon Poulton, of the University of Leeds, who co-authored the study, said: "The neat point about this study is that it shows just how critical an absence of oxygen, rather than the presence of toxic sulphide, was to the survival of animal life. We found that marine organisms were able to rapidly recolonise areas where oxygen became available."

共同作者，里茲大學的Simon Poulton教授說：「這項研究的亮點在於顯示出對於動物能否生存來說，環境缺氧的致命程度遠較含有毒性硫化物高上許多。另外我們也發現當某些地區開始含有氧氣時，海洋生物便會迅速重新遷居回該區域。」

University of Edinburgh. "Ancient rocks reveal how Earth recovered from mass extinction." ScienceDaily. ScienceDaily, 19 July 2016. <www.sciencedaily.com/releases/2016/07/160719123023.htm>.