科學家證實了地球歷史上規模最大的滅絕事件的元凶
最新研究完整重建了二疊紀和三疊紀之際的事件
2.52億年前，在二疊紀進入到三疊紀之際，當時地球上生存的大多數生命形式就此滅亡。最近德國基爾亥姆霍茲海洋研究中心(GEOMAR)、德國地質科學研究中心(GFZ)和不同國家的科學家互相合作，利用最新的分析技術並用電腦模型詳細的計算結果，首次明確地重建出是什麼樣的地球化學過程，造成了這次前所未見的生物危機。研究今日發表在期刊《自然―地球科學》(Nature Geoscience)。
這幅示意圖根據Jurikova等人在2020年的發現，描繪了二疊紀―三疊紀大滅絕開始時的狀況。畫家為羅馬大學PaleoFactory的Dawid Adam Iurino 。
生命在地球上的歷史雖然源遠流長，卻也歷經波折。不止一次，在某個時刻當下生活在地球上的物種絕大多數都走向滅亡，蓬勃發展的生物多樣性也再次陷入低谷。每次這類事件發生都會改變演化的方向。其中最嚴重的大滅絕事件發生在2億5200萬年前左右，短短幾千年之內，大約四分之三的陸地生物與百分之95的海洋生物就此消失，也標示了二疊紀的結束與三疊紀的開始。
在今日的西伯利亞發生的超大型火山活動，以及從海床釋放的大量甲烷可能引起了二疊紀―三疊紀大滅絕，是科學家長久以來的討論對象。然而造成大滅絕的確切原因以及事件的發生順序卻還是眾說紛紜。由歐盟提供經費，德國基爾亥姆霍茲海洋研究中心的教授Anton
Eisenhauer博士與德國地質科學研究中心領導了「地球基準」(BASE-LiNE
Earth)計畫，最近他們和德國、義大利和加拿大的科學家在該計畫的框架之下，利用尖端的分析技術和新穎的地球化學模擬方法，首度成功地把當時整串事件的發生過程給確切重建出來。研究結果發表在國際期刊《自然―地球科學》。
地球基準團隊的研究運用了一種過去經常受到忽視的環境紀錄：腕足類的殼體化石。研究第一作者Hana
Jurikova表示：「這些像是蚌殼的生物在地球上生活了超過五億年。我們進行分析時利用了採自南阿爾卑斯山，保存狀況良好的腕足類化石。它們在2億5200萬年前沉積在特提斯洋的淺海陸棚底部，記錄了滅絕事件不久之前以及剛開始的環境狀況。」這篇研究是地球基準計畫的一部份，同時也是Jurikova在GEOMAR的博士論文內容。
透過測量殼體化石中不同的硼同位素含量，團隊可以追蹤2億5200萬年前海水pH值的變化過程。由於海水pH值和大氣中的二氧化碳含量關係密切，因此他們也能把後者重建出來。團隊分析時使用了GEOMAR的高精度同位素分析儀，並且利用GFZ最先進的大尺寸二次離子質譜儀進行高解析度的微量分析。
GEOMAR的Marcus
Gutjahr是研究共同作者，他說：「利用這項技術我們不只可以重建大氣二氧化碳濃度的演變過程，還能確切地推論原因是火山活動。至於另外一項被認為可能讓情況加劇的原因――天然氣水合物分解――在我們的數據看來則相當不可能。」
接下來，團隊把他們的硼同位素數據和其他根據碳同位素的研究結果，輸入到電腦裡的地球化學模型，藉此模擬地球當時發生的作用。結果顯示在滅絕事件一開始，火山排放到大氣的大量二氧化碳造成的暖化和海洋酸化程度，就已經相當致命並造成海裡的鈣化生物滅亡。不只如此，釋放到大氣的二氧化碳還更進一步造成溫室效應，使整個地球的溫度上升，陸地上的化學風化作用也跟著變強。
從河流和海岸運輸到海裡的營養鹽因而增加，數千年下來讓海洋的營養鹽過剩。結果便是海洋出現大規模的缺氧現象以及元素循環的過程整個遭到改變。Jurikova博士總結：「這些環環相扣、生命賴以為生的循環和作用就像骨牌一樣接連倒塌，最後造成我們在二疊紀和三疊紀交界觀察到的，程度堪稱浩劫的大滅絕事件。」
這項研究根據的框架為歐盟資助的ITN計畫「地球基準」，該計畫首度有系統地把腕足類當作一種環境紀錄來研究，同時運用改良過或最新發展出來的方法來進行相關分析。「要和我們目前的成果一樣，把2億5000萬年以前發生的過程重建到如此詳細的程度，如果沒有這些最新技術是很難辦到的。」GEOMAR的教授Anton
Eisenhauer博士強調。他是這項新研究的共同作者，之前負責統籌地球基準計畫。「不只如此，這些新方法也能應用到其他科學領域。」
Driver of the largest mass extinction
in the history of the Earth identified
New study provides a comprehensive reconstruction
of the Permian-Triassic boundary event
252 million years ago, at the transition
from the Permian to the Triassic epoch, most of the life forms existing on
Earth became extinct. Using latest analytical methods and detailed model
calculations, scientists from the GEOMAR Helmholtz Centre for Ocean Research
Kiel, in cooperation with the Helmholtz Centre Potsdam GFZ German Research
Centre for Geosciences and international partners, have now succeeded for the
first time to provide a conclusive reconstruction of the geochemical processes
that led to this unprecedented biotic crisis. The study has been published
today in the journal Nature Geoscience.
Life on Earth has a long, but also an extremely
turbulent history. On more than one occasion, the majority of all species
became extinct and an already highly developed biodiversity shrank to a minimum
again, changing the course of evolution each time. The most extensive mass
extinction took place about 252 million years ago. It marked the end of the
Permian Epoch and the beginning of the Triassic Epoch. About three quarters of
all land life and about 95 percent of life in the ocean disappeared within a few
thousands of years only.
Gigantic volcanic activities in today's Siberia and
the release of large amounts of methane from the sea floor have been long
debated as potential triggers of the Permian-Triassic extinction. But the exact
cause and the sequence of events that led to the mass extinction remained
highly controversial. Now, scientists from Germany, Italy and Canada, in the
framework of the EU-funded project BASE-LiNE Earth led by Prof. Dr. Anton
Eisenhauer from GEOMAR Helmholtz Centre for Ocean Research Kiel in cooperation
with the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences,
have for the first time been able to conclusively reconstruct the entire
cascade of events at that time using cutting-edge analytical techniques and
innovative geochemical modelling. The study has been published today in the
international journal Nature Geoscience.
For their study, the BASE-LiNE Earth team used a
previously often neglected environmental archive: the shells of fossil
brachiopods. “These are clam-like organisms that have existed on Earth for more
than 500 million years. We were able to use well-preserved brachiopod fossils
from the Southern Alps for our analyses. These shells were deposited at the
bottom of the shallow shelf seas of the Tethys Ocean 252 million years ago and
recorded the environmental conditions shortly before and at the beginning of
extinction”, explains Dr. Hana Jurikova. She is first author of the study,
which she conducted as part of the BASE-LiNE Earth project and her doctoral
thesis at GEOMAR.
By measuring different isotopes of the element boron
in the fossil shells, the team was able to trace the development of the pH
values in the ocean 252 million years ago. Since seawater pH is tightly coupled
to the CO2 concentration in the atmosphere, the reconstruction of
the latter was also possible. For the analyses, the team used high-precision
isotope analyses at GEOMAR as well as high-resolution microanalyses on the
state-of-the-art large-geometry secondary ion mass spectrometer (SIMS) at GFZ.
“With this technique, we can not only reconstruct the
evolution of the atmospheric CO2 concentrations, but also clearly
trace it back to volcanic activity. The dissolution of methane hydrates, which
had been suggested as a potential further cause, is highly unlikely based on
our data”, explains Dr. Marcus Gutjahr from GEOMAR, co-author of the study.
As a next step, the team fed their data from the
boron and additional carbon isotope-based investigations into a computer-based
geochemical model that simulated the Earth’s processes at that time. Results
showed that warming and ocean acidification associated with the immense
volcanic CO2 injection to the atmosphere was already fatal and led
to the extinction of marine calcifying organisms right at the onset of the
extinction. However, the CO2 release also brought further
consequences; with increased global temperatures caused by the greenhouse
effect, chemical weathering on land also increased.
Over thousands of years, increasing amounts of
nutrients reached the oceans via rivers and coasts, which then became
over-fertilized. The result was a large-scale oxygen depletion and the
alteration of entire elemental cycles. “This domino-like collapse of the
inter-connected life-sustaining cycles and processes ultimately led to the
observed catastrophic extent of mass extinction at the Permian-Triassic
boundary,” summarizes Dr. Jurikova.
The study was conducted within the framework of the
EU-funded ITN project BASE-LiNE Earth, in which the use of brachiopods as an
environmental archive was systematically studied for the first time, and
relevant analytical methods were improved and newly developed. “Without these
new techniques it would be difficult to reconstruct environmental processes
more than 250 million years ago in the same level of detail as we have done
now”, emphasizes Prof. Dr. Anton Eisenhauer from GEOMAR, the former BASE-LiNE
Earth project coordinator and co-author of the new study, “in addition, the new
methods can be applied for other scientific applications”.
原始論文：Hana Jurikova,
Marcus Gutjahr, Klaus Wallmann, Sascha Flögel, Volker Liebetrau, Renato
Posenato, Lucia Angiolini, Claudio Garbelli, Uwe Brand, Michael Wiedenbeck,
Anton Eisenhauer. Permian–Triassic mass extinction pulses driven by
major marine carbon cycle perturbations. Nature Geoscience, 2020;
DOI: 10.1038/s41561-020-00646-4
引用自：Helmholtz Centre for Ocean Research Kiel
(GEOMAR). "Driver of the largest mass extinction in the history of the
Earth identified."
沒有留言:
張貼留言