不起眼的苔蘚卻幫助地球形成了富含氧氣的大氣層

原始網址：www.sciencedaily.com/releases/2016/08/160815185610.htm

Humble moss helped create our oxygen-rich atmosphere

不起眼的苔蘚卻幫助地球形成了富含氧氣的大氣層

The evolution of the first land plants including mosses may explain a long-standing mystery of how Earth's atmosphere became enriched with oxygen, according to an international study led by the University of Exeter.

根據一則由英國艾希特大學進行的國際研究，包含蘚苔在內的植物成功演化出在陸地上生活的能力，或許能解釋一項長久以來的疑問：地球大氣如何變得富含氧氣？

Oxygen in its current form first appeared in Earth's atmosphere some 2.4 billion years ago, in an incident known as the Great Oxidation Event. However, it was not until roughly 400 million years ago that this vital compound first approached modern levels in the atmosphere. This shift steered the trajectory of life on Earth and researchers have long debated how oxygen rose to modern concentrations.

大約在24億年前發生了稱作「大氧化事件(Great Oxidation Event)」的劇變後，地球大氣層的組成當中第一次出現了氧氣。然而，還要再等到4億年前左右，這個重要成分在大氣中的濃度才會首度攀升至跟現今十分接近。這個轉變引領了地球生物的演化方向，而研究人員對氧氣如何提升至現今的濃度也已經爭論許久。

In a study published in the journal Proceedings of the National Academy of Sciences, Professor Tim Lenton, of the University of Exeter, and his colleagues theorised that the earliest land plants, which colonised the land from 470 million years ago onwards, are responsible for the levels of oxygen that sustains our lives today. Their emergence and evolution permanently increased the flux of organic carbon into sedimentary rocks, the primary source for atmospheric oxygen, thus driving up oxygen levels in a second oxygenation event and establishing a new, stable oxygen cycle.

艾希特大學的Tim Lenton和他的同僚在刊登於《美國國家科學院院刊》(Proceedings of the National Academy of Sciences)的研究中，提出了一項理論認為自4億7000萬年前開始最早往陸地拓殖的植物，讓氧氣濃度上升至今日人類得以維生的程度。它們的出現和演化永久增加了有機碳進入沉積岩的速率，由於這個過程是大氣中氧氣的主要來源，因此這促使第二次氧化事件發生並提升了大氣氧濃度，使得氧循環進入了一種全新的穩定狀態。

Earth's early plant biosphere consisted of simple bryophytes, such as moss, which are non-vascular -- meaning they do not have vein-like systems to conduct water and minerals around the plant. Using computer simulations, the researchers first estimated that these plants could have generated roughly 30% of today's global terrestrial net primary productivity by about 445 million years ago.

地球最早的植物生物圈成員之一為簡單的苔蘚植物門(bryophyte)，包含蘚苔在內的這些植物缺乏維管束(vascular)構造，意味著它們不具有連通整株植物可以用來傳輸礦物質和水分的脈絡狀系統。研究人員利用電腦模擬的結果，最初預估約莫在4億4500萬年前，這些植物的生產力已經可以達到當今全球陸地淨初級生產量(net primary productivity)的30%左右。

When the properties of modern bryophytes were taken into account, including their elemental composition and effects on rock weathering, they found that modern levels of atmospheric oxygen were achieved by 420 to 400 million years ago, consistent with independent evidence.

當研究人員將現存苔蘚植物的性質，像是元素組成以及對岩石風化作用的影響納入模型當中，他們發現大氣氧濃度在4億2000萬年至4億年前到達與現在相同的程度，這跟從另一種獨立證據推估出來的時間點相符。

These findings therefore suggest that the first land plants, such as the humble moss, created the stable oxygen-rich atmosphere that allowed large, mobile, intelligent animal life, including humans, to evolve.

因此，這些發現指出最初登陸的植物，像是不起眼的苔蘚卻是形成富含氧氣的穩定大氣層的幕後推手，並進一步讓大型、活動力強、有心智能力的動物，包含人類在內的生命得以演化出來。

Professor Tim Lenton, of the University of Exeter, said: "It's exciting to think that without the evolution of the humble moss, none of us would be here today. Our research suggests that the earliest land plants were surprisingly productive and caused a major rise in the oxygen content of Earth's atmosphere."

艾希特大學的 Tim Lenton教授說：「若這些不起眼的苔蘚從未演化出來，則今日我們之中的任何一位都不會站在這裡，這個想法相當具有啟發性。我們的研究主張最初的陸生植物生產力其實相當驚人，而促使地球大氣層的氧含量大幅提升。」

引用自：University of Exeter. "Humble moss helped create our oxygen-rich atmosphere." ScienceDaily. ScienceDaily, 15 August 2016. 

論文來源：Timothy M. Lenton, Tais W. Dahl, Stuart J. Daines, Benjamin J. W. Mills, Kazumi Ozaki, Matthew R. Saltzman, Philipp Porada. Earliest land plants created modern levels of atmospheric oxygen. Proceedings of the National Academy of Sciences, 2016

以闡明2004年印度洋大地震及海嘯成因為目標的國際海洋鑽探計畫

原文網址：www.sciencedaily.com/releases/2016/08/160808091256.htm

International ocean drilling expedition to understand causes of the Indian Ocean 2004 earthquake and tsunami

以闡明2004年印度洋大地震及海嘯成因為目標的國際海洋鑽探計畫

The devastating earthquake that struck North Sumatra and the Andaman and Nicobar Islands on Boxing Day (26 December) in 2004 caused a tsunami that inundated coastal communities around the Indian Ocean, killing over 250,000 people in 14 countries. That earthquake was caused by a slip on a subduction zone plate boundary fault beneath the eastern Indian Ocean.

在2004年節禮日(12月26日)當天，一場毀天滅地的大地震襲擊了蘇門答臘北部和安達曼—尼科巴群島(Andaman and Nicobar Islands)，同時引發的海嘯淹沒了印度洋周遭的沿海地帶，造成14個國家超過25萬人因此罹難。這場地震的成因是位於東印度洋板塊邊界，隱沒帶內部的斷層發生滑移所造成。

Now, over the coming weeks, a team of international researchers are returning to offshore Sumatra to collect marine sediments, rocks and fluids from this particular zone for the first time to gain a better understanding of the materials and to collect data for predicting how they behave in fault zones to generate large earthquakes.

時至今日，一組國際研究團隊在接下來的數周將會返回蘇門答臘外海，首次針對此區域的海洋沉積物、岩石和流體進行採樣，以更加瞭解這些物質的性質，並且蒐集數據來預測它們在斷層帶的行為如何導致大地震發生。

Throughout August and September the researchers, including experts from Ocean and Earth Science at the University of Southampton will spend two months on board the drilling vessel JOIDES Resolution as part of the International Ocean Discovery Programme (IODP). The Expedition, number 362 of the IODP, involves 33 scientists and two educators from 13 countries including Professors Lisa McNeill and Tim Henstock from the University of Southampton. Professor McNeill is one of the Expedition leaders along with Associate Professor Brandon Dugan of the Colorado School of Mines and Dr Katerina Petronotis of the IODP.

作為國際海洋發現計畫(IODP)中的一部分，包含南安普敦大學海洋與地球科學專家在內的研究人員，將會利用八月及九月兩個月的時間在鑽探船「聯合果敢號」上進行研究。來自13個國家的33名科學家和2名教育學者參與了這班IODP中編號為362的研究航次，其中包括了南安普敦大學的教授 Lisa McNeill和Tim Henstock。 McNeill教授是這次科學考察的主持人之一，另外兩名主持人則是科羅拉多礦業學院的副教授Brandon Dugan和 IODP的 Katerina Petronotis博士。

"We are very excited that the project is about to start as it has taken many years of preparation and the dedication of a large team of scientists from around the world," said Professor McNeill. "We have an excellent team onboard and we hope the results will help us understand what controls the size of the very largest earthquakes on Earth, particularly following the enormous numbers of casualties due to subduction earthquakes and tsunamis in the last 10-15 years.

「由世界各地科學家組成的團隊投注大量心力籌備多年的計畫終於要開始實行，對此我們感到十分興奮。」 McNeill教授表示。「我們在這艘船上擁有一組相當優秀的團隊，希望成果可以讓我們瞭解是什麼機制決定了地球上超大規模地震的大小，尤其是在過去10到15年來有許多人於隱沒帶產生的地震及伴隨的海嘯事件中罹難之後。」

"The Boxing Day earthquake of 2004 and the Japan Tohoku-oki earthquake in 2011 both ruptured to much shallower depths than expected, producing very large earthquakes and tsunami, and prompting a re-evaluation of earthquake slip potential and of the properties of shallow subduction faults," Professor McNeill continued. "Subsequent large magnitude earthquakes have struck this margin since 2004, including unusually large earthquakes in the Indian plate offshore North Sumatra in 2012. Therefore developing a better understanding of earthquake and tsunami behavior and potential is a priority for local communities, for the wider Indian Ocean, and for related subduction zones."

「2004年節禮日地震和2011年日本東北衝地震產生的破裂都延伸至比預期中淺了許多的地方，因而造成晃動相當劇烈的地震及巨型海嘯。這促使我們去重新評估淺層隱沒帶斷層發生滑移而產生地震的可能性及斷層本身的性質。」 McNeill教授繼續說。「自2004年開始這道板塊邊界後來也發生了數起大規模地震，包括2012年發生在蘇門答臘北部，印度板塊外海地區一場非常大型的地震。因此對當地居民，甚至是生活在印度洋周遭及其他類似隱沒帶附近的人民而言，當務之急是要更深入了解地震與海嘯的模式和發生的可能性。」

Professor McNeill explained that the North Sumatran subduction margin has an unusual structure and morphology that is likely influenced by the properties of the sediments and rocks forming the margin.

據McNeill教授解釋，蘇門答臘北部的隱沒性板塊邊界可能受到岩石及沉積物組成的性質影響，造成其構造與形貌相當特殊。

"Although our understanding of this margin's structure and development has increased enormously since 2004 due to marine geophysical data collection, as yet very little is known of the properties of the materials that make up this subduction zone," she continued. "This project will investigate how materials coming into the system drive shallow earthquake rupture and influence the shape of the continental margin. Our ultimate goal is to understand the hazard potential for this margin, and eventually others with similar material properties and margin morphology.

「雖然自2004年以來從當地海域蒐集了大量地球物理觀測數據，讓我們對此板塊邊界的構造及發育增加了許多瞭解，但是關於隱沒帶組成物質的性質我們仍所知甚少。」她繼續解釋。「這項計畫將會研究這些物質如何參與誘發淺層地震發生的系統，以及對板塊邊界形貌的影響。我們的終極目標是瞭解這段板塊邊緣可能發生的潛在災害，最後可以推及其他組成性質和型態類似的板塊邊緣。」

"This ocean drilling expedition will for the first time drill scientific boreholes within the sediments entering this subduction zone, including the layer of sediment that eventually develops into the earthquake-generating fault," Professor Henstock explained. "We know the sediments are of deep sea and terrestrial origin, including those eroded from the high Himalayas and transported thousands of kilometres into the Bay of Bengal and eastern Indian Ocean. But we do not know how the sediments change as they become physically and chemically altered as the sediment section builds up to 4-5 km thickness before reaching the subduction zone.

「這次的海洋鑽探計畫是史上首度對進入這條隱沒帶的沉積物進行鑽井的科學計畫。包括沉積物在內，鑽探深度最終會到達產生地震的斷層所在位置。」 Henstock教授如此解說。「我們知道這些沉積物的來源為深海及陸源，甚至含有從高聳的喜馬拉雅山侵蝕下來，傳輸數千公里直到孟加拉灣和東印度洋的沉積物。但我們仍不瞭解在到達隱沒帶之前，這些沉積物在累積4-5公里厚的過程中發生的物理化學變化。」

"Burial and increased temperatures also affect fluids within the sediment pile, and these are very important for earthquake fault behavior," Professor Henstock concluded. "Sampling and measuring the properties of the materials in situ and then extrapolating their properties to greater burial depths using modeling techniques and lab experiments will be important goals of this project."

「埋藏作用跟逐漸升高的溫度會影響沉積物當中的流體，而流體會對地震斷層的行為產生深遠影響。」 Henstock教授總結。「從現地採集這些物質的樣本並且測量其性質之後，利用模擬技術和實驗室試驗來外推這些性質在埋藏深度極深時的數值，是這項計畫的重要目標之一。」

引用自：University of Southampton. "International ocean drilling expedition to understand causes of the Indian Ocean 2004 earthquake and tsunami." ScienceDaily. ScienceDaily, 8 August 2016. 

地函似乎具有驅動板塊構造運動的作用

原始網址：www.sciencedaily.com/releases/2016/07/160728143525.htm

Earth's mantle appears to have a driving role in plate tectonics

地函似乎具有驅動板塊構造運動的作用

Deep down below us is a tug of war moving at less than the speed of growing fingernails. Keeping your balance is not a concern, but how the movement happens has been debated among geologists.

在我們腳下正發生一場節奏比指甲生長速度還慢的拔河比賽。要在其上保持平衡並不是什麼問題，但這項運動如何發生卻是地質學家長久以來爭論不休的議題。

New findings from under the Pacific Northwest Coast by University of Oregon and University of Washington scientists now suggest a solution to a mystery that surfaced when the theory of plate tectonics arose: Do the plates move the mantle, or does the mantle move the plates.

奧勒岡大學和華盛頓大學的科學家對太平洋西北岸下方進行了新研究之後，提出了一項理論可以解答自板塊構造學說問世以來就有的一件謎題：到底是板塊使地函流動，或是地函讓板塊移動？

The separation of tectonic plates, the researchers proposed in a paper online ahead of print in the journal Nature Geoscience, is not simply dictating the flow of the gooey, lubricating molten material of the mantle. The mantle, they argue, is actually fighting back, flowing in a manner that drives a reorientation of the direction of the plates.

研究人員在期刊《自然—地質科學》(Nature Geoscience)出刊前的線上版論文中表示，地函的黏滑物質往哪裡流動並非受板塊的分離運動單方面支配。他們主張地函事實上也會有所反抗，它的流動在某種程度上也會重新調整板塊運動的方向。

The new idea is based on seismic imaging of the Endeavor segment of the Juan de Fuca Plate in the Pacific Ocean off Washington and on data from previous research on similar ridges in the mid-Pacific and mid-Atlantic oceans.

這項新理論主要奠基於來自華盛頓外海，太平洋的胡安‧德富卡板塊中(Juan de Fuca Plate)的Endeavor段得到的震測影像，以及過往對太平洋及大西洋中其他類似洋脊的研究成果。

"Comparing seismic measurements of the present mantle flow direction to the recent movements of tectonic plates, we find that the mantle is flowing in a direction that is ahead of recent changes in plate motion," said UO doctoral student Brandon P. VanderBeek, the paper's lead author. "This contradicts the traditional view that plates move the mantle."

「比較震測影像呈現出來的現今地函流動方向以及近期板塊的移動方向，我們發現地函的流動方向竟然早於板塊運動近期發生的改變之前。」此篇論文的第一作者，奧勒岡大學的博士生 Brandon P. VanderBeek表示。「這跟傳統中認為板塊拖曳地函移動的論點相悖。」

While the new conclusion is based on a fraction of such sites under the world's oceans, a consistent pattern was present, VanderBeek said. At the three sites, the mantle's flow is rotated clockwise or counterclockwise rather than in the directions of the separating plates. The mantle's flow, the researchers concluded, may be responsible for past and possibly current changes in plate motion.

VanderBeek 說雖然這項新結論僅根據全世界海洋中上述位置一部分的觀察結果而來，但它們之間確實有相當一致的模式存在著。在這三個地點，地函流動方向跟板塊分離方向之間並不一致，而是往順時針或逆時針偏差了一個角度。研究人員總結，地函流動可能造成過去，甚至是當下正在發生的板塊運動方向的改變。

The research -- funded through National Science Foundation grants to the two institutions -- also explored how the supply of magma varies under mid-ocean ridge volcanoes. The researchers conducted a seismic experiment to see how seismic waves moved through the shallow mantle below the Endeavor segment.

這項研究由美國國家科學基金會資助上述兩個機構來進行，同時也探討了中洋脊火山之下的岩漿供應隨空間變化的情形。研究人員進行震測實驗來觀察地震波在Endeavor段之下的淺層地函中會如何行進。

They found that the middle of the volcanic segment, where the seafloor is shallowest and the inferred volcanic activity greatest, the underlying mantle magma reservoir is relatively small. The ends, however, are much deeper with larger volumes of mantle magma pooling below them because there are no easy routes for it to travel through the material above it.

他們發現火山帶的中間地段，也就是海床最淺且推測火山活動最劇烈處，底下的地函岩漿庫相對而言是比較小的。然而，位於較深處的兩端其下方卻有大量的地函岩漿集中於此，這是因為此處並沒有捷徑可以讓這些岩漿穿越上方的物質。

Traditional thinking had said there would be less magma under the deep ends of such segments, known as discontinuities.

傳統觀點認為在這些段落最深兩端稱作「不連續帶」的地方，其下的岩漿會比較少。

"We found the opposite," VanderBeek said. "The biggest volumes of magma that we believe we have found are located beneath the deepest portions of the ridges, at the segment ends. Under the shallow centers, there is much less melt, about half as much, at this particular ridge that we investigated.

「我們發現的事實恰好相反。」 VanderBeek說。「我們認為我們發現的岩漿庫中體積最大者正好位於洋脊兩端最深的地方。在我們研究的這段洋脊深度較淺的中央地帶，下方岩漿庫的體積頂多只有最大者的一半。」

"Our idea is that the ultimate control on where you have magma beneath these mountain ranges is where you can and cannot take it out," he said. "At the ends, we think, the plate rips apart much more diffusely, so you are not creating pathways for magma to move, build mountains and allow for an eruption."

「我們的想法是，控制這些洋脊下方岩漿庫大小的根本因素是有沒有通路可以讓它們流出來。」他說。「我們認為在洋脊兩端，板塊撕裂造成的傷口較中央更加不平整，因此無法形成可以讓岩漿流動的通路，連帶使岩漿無法在此噴發而形成山脊。」

引用自：University of Oregon. "Earth's mantle appears to have a driving role in plate tectonics." ScienceDaily. ScienceDaily, 28 July 2016. 

新的化石證據支持了首次大滅絕是由早期動物一手鑄成的理論

原始網址：www.sciencedaily.com/releases/2016/07/160729132912.htm

New fossil evidence supports theory that first mass extinction engineered by early animals

新的化石證據支持了首次大滅絕是由早期動物一手鑄成的理論

Newly discovered fossil evidence from Namibia strengthens the proposition that the world's first mass extinction was caused by "ecosystem engineers" -- newly evolved biological organisms that altered the environment so radically it drove older species to extinction.

從納米比亞新發現的化石證據鞏固了世上首度大滅絕是由「生態工程師」造成的論點。也就是新演化出來的生物劇烈改變環境而驅使原有生物走向滅絕。

The event, known as the end-Ediacaran extinction, took place 540 million years ago. The earliest life on Earth consisted of microbes -- various types of single-celled organisms. These held sway for more than 3 billion years, when the first multicellular organisms evolved. The most successful of these were the Ediacarans, which spread around the globe about 600 million years ago. They were a largely immobile form of marine life shaped like discs and tubes, fronds and quilted mattresses.

這起稱作「埃迪卡拉紀末期滅絕事件」(end-Ediacaran extinction)的大滅絕發生於5.4億年前。地球最早的生命是由微生物組成，包含了各式各樣的單細胞生物。直到第一群多細胞生物演化出來以前，它們支配了地球超過30億年。這些多細胞生物中最成功的一群為埃迪卡拉生物(Ediacarans)，在6億年前牠們已經散佈至全球各地。埃迪卡拉生物大多是無法移動的海洋生物，外表呈現盤狀、管狀、葉狀或是像厚重的床墊一樣。

After 60 million years, evolution gave birth to another major innovation: metazoans, the first animals. Metazoans could move spontaneously and independently at least during some point in their life cycle and sustain themselves by eating other organisms or what other organisms produce. Animals burst onto the scene in a frenzy of diversification that paleontologists have labeled the Cambrian explosion, a 25 million-year period when most of the modern animal families -- vertebrates, mollusks, arthropods, annelids, sponges and jellyfish -- came into being.

在6千萬年之後，出現了另一個演化史上的重大變革：第一群後生動物(metazoan)，也就是一般所稱的動物出現了。後生動物在牠們的生命週期中至少有一個階段可以自發且獨立地移動，並以攝食其他生物或是其他生物的產物維生。很快地動物便進入古生物學家稱作寒武紀大爆發的時期，在這段2500萬年的時光中，動物的多樣性爆炸性地增長。大多數現今可見的動物種類，像是脊索動物、軟體動物、節肢動物、環節動物、海綿和水母，便是在這段期間開始現身。

"These new species were 'ecological engineers' who changed the environment in ways that made it more and more difficult for the Ediacarans to survive," said Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University, who directed the new study described in the paper titled "A mixed Ediacaran-metazoan assemblage from the Zaris Sub-basin, Namibia," published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

「這些新物種為『生態工程師』(ecological engineer)，牠們改變了環境而使得埃迪卡拉生物越來越難以生存。」 Simon Darroch說。這位范德比大學地球與環境科學的助理教授於發表在期刊《古地理學、古氣候學、古生態學》(Palaeogeography, Palaeoclimatology, Palaeoecology)，題名為「A mixed Ediacaran-metazoan assemblage from the Zaris Sub-basin, Namibia」的論文中描述了他所進行的新研究。

Darroch and his colleagues report that they have found one of the best-preserved examples of a mixed community of Ediacarans and animals, which provides the best evidence of a close ecological association between the two groups.

Darroch和他的同僚發表說他們於這處場址發現的埃迪卡拉生物和動物混居而成的群集為保存情況最良好的一例，這給他們相當有力的證據可以證實這兩群生物之間有相當緊密的生態關係。

"Until this, the evidence for an overlapping ecological association between metazoans and soft-bodied Ediacaran organisms was limited," Darroch said. "Here, we describe new fossil localities from southern Namibia that preserve soft-bodied Ediacara biota, enigmatic tubular organisms thought to represent metazoans and vertically oriented metazoan trace fossils. Although the precise identity of the tracemakers remains elusive, the structures bear several striking similarities with a cone-shaped organism called Conichnus that has been found in the Cambrian period."

「在這項發現之前，很少有證據顯示後生動物以及體態柔軟的埃迪卡拉生物混居而成的生態群落。」 Darroch說。「我們在這裡記述的化石地點位於納米比亞南部，這裡保存了構造柔軟的埃迪卡拉生物相、被認為是後生動物的謎樣管狀生物，以及垂直方向的後生動物生痕化石(trace fossil)。雖然留下這些生痕的動物確切身分仍不明朗，但其構造跟寒武紀發現的錐狀生物化石Conichnus之間有著驚人的相似性。」

In a previous paper that Darroch and his collaborators published last September, they reported on a fossil record that showed stressed-looking communities of Ediacara associated with a suite of animal burrows.

在 Darroch和他的同僚於去年九月發表的前一份研究中，他們發表的化石紀錄顯示跟動物挖出來的連串洞穴一起出現的埃迪卡拉生物群有受到壓迫的跡象。

"With this paper we're narrowing in on causation; we've discovered some new fossil sites that preserve both Ediacara biota and animal fossils (both animal burrows -- 'trace fossils' -- and the remains of animals themselves) sharing the same communities, which lets us speculate about how these two very different groups of organisms interacted," he said.

「連同跟這篇論文我們能做出更確實的推論。我們新發現的化石場址保存了處於同一群集的埃迪卡拉生物群和動物化石(包括動物挖出來的洞穴，即『生痕化石』，以及動物本體的遺骸)，這讓我們可以推測兩群截然不同的生物之間會有怎麼樣的互動。」他說。

"Some of the burrow fossils we've found are usually interpreted as being formed by sea anemones, which are passive predators that may have preyed upon Ediacaran larvae. We've also found stands of Ediacaran frondose organisms, with animal fossils preserved in place coiled around their bases. In general, these new fossil sites reveal a snapshot of a very unusual 'transitional' ecosystem existing right before the Cambrian explosion, with the last of the Ediacara biota clinging on for grim death, just as modern-looking animals are diversifying and starting to realize their potential."

「我們發現的一些洞穴化石通常會被解讀為由海葵形成，這種被動掠食者可能會攝食埃迪卡拉生物的幼苗。我們也發現某些聚集成叢的埃迪卡拉葉狀生物會有動物化石盤繞在牠們的基部。總歸來說，這些新化石場址顯現了寒武紀大爆發即將到來前，生態系正處於十分特殊的『過渡期』的那一瞬間。當跟現代動物相似的動物趨向多樣化並開始了解到牠們擁有的無窮潛能時，最後的埃迪卡拉生物群正在做最後一絲掙扎。」

Although Darroch is studying events that took place 540 million years ago, he believes there is a message relevant for today. "There is a powerful analogy between Earth's first mass extinction and what is happening today," he said. "The end-Ediacaran extinction shows that the evolution of new behaviors can fundamentally change the entire planet, and today we humans are the most powerful 'ecosystems engineers' ever known."

雖然Darroch探討的事件發生於5.4億年前，他認為這些研究傳遞出來的訊息跟現在的世界有密切關係。「地球的第一次大滅絕跟當下正在發生的生物滅絕可說是非常相似。」他說。「埃迪卡拉紀末期滅絕事件告訴我們生物新演化出來的行為模式可以從根本上改變整個星球，而現今我們這些人類即是有史以來出現過影響力最強的『生態工程師』。」

引用自：Vanderbilt University. "New fossil evidence supports theory that first mass extinction engineered by early animals." ScienceDaily. ScienceDaily, 29 July 2016. 

科學家在暖期氣候的重建上終於有了等待許久的突破性進展

原始網址：www.sciencedaily.com/releases/2016/07/160718133009.htm

Long-awaited breakthrough in the reconstruction of warm climate phases

科學家在暖期氣候的重建上終於有了等待許久的突破性進展

Scientists from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) have overcome a seeming weakness of global climate models. They had previously not been able to simulate the extreme warm period of the Eocene. One aspect of this era that particularly draws interests to climatologists: It was the only phase in recent history when greenhouse gas concentration was as high as researchers predict it to be for the future. The AWI scientists have now found that the apparent model weakness is due to a misinterpretation of the temperature indicator TEX86. These molecules, which are produced by archaea do not record the surface temperature of the ancient ocean as expected, but rather the temperature of water depths up to 500 metres. In the current issue of the journal Nature Geoscience, the scientists report on this new finding which has now made it possible to correctly simulate the temperature distribution of the Eocene in climate models.

阿爾弗雷德•韋格納研究所暨亥姆霍茲極地與海洋研究中心(AWI)的科學家克服了全球氣候模型中一個相當明顯的缺陷：先前科學家無法重新模擬出始新世(Eocene)時的極端暖期。這段時期特別吸引氣候學家的其中一個方面是，這是近代史上唯一溫室氣體濃度相當高，跟氣候模型預測的未來溫室氣體濃度相仿的時期。AWI的科學家發覺模型中的明顯缺陷是來自於錯誤解讀溫度指標TEX86的含意。這些由古菌(Archaea)製造的分子並不如預期記錄了古代海洋的表層溫度，而是深達500公尺的水溫。在當期《自然—地質科學》(Nature Geoscience)期刊中，科學家發表的這項新發現讓氣候模型有機會能正確模擬出始新世時的全球氣溫分布模式。

Climate scientists often hear the same complaint: How can climate models accurately predict the future of our planet if it is not even possible to correctly reproduce the climate of the past? One of the unsolved problems was that all previous attempts to simulate the extreme temperatures of the Eocene with climate models failed.

氣候學家經常聽到人們一再質疑說：如果氣候模型連正確地重現過去的氣候都無法做到，那怎麼可能用它來準確預測地球未來的命運？在種種尚未解決的難題中，其一便是過往嘗試以氣候模型模擬始新世的極端高溫時都以失敗收場。

At that time, 49 to 55 million years ago, the carbon dioxide content of the air was likely more than 1000 ppm (parts per million) -- i.e. at least two times the current greenhouse gas concentration. The earth warmed up so strongly that the icesheets on Greenland and Antarctica disappeared. Instead of ice crystals, palm trees grew there. "Until recently, we believed that the sea surface temperature near the North Pole at the time was 23 degrees Celsius; in Antarctica, it was believed to have been more than 30 degrees Celsius," says Dr Thomas Laepple, climate researcher at the AWI Potsdam.

在4900萬年至5500萬年前，當時大氣二氧化碳濃度可能超過1000 ppm(百萬分之一)，也就是現今溫室氣體濃度的至少兩倍以上。地球加溫的情形之嚴重，連覆蓋在格陵蘭和南極大陸的冰棚都融化殆盡。當時在那裏見到的可不是冰晶，而是繁茂生長的棕櫚樹。「直到最近我們仍然確信當時北極附近的海水表面溫度為23℃；在南極則可能超過30℃。」波茨坦大學的AWI氣候研究人員， Thomas Laepple表示。

These temperature estimates were based on data from the climate indicator TEX86. This abbreviation stands for a ratio of specific organic compounds produced by archaea, depending on the water temperature in which they lived. "Archaea are unicellular organisms that can in part withstand surprisingly high ambient temperatures. The molecules of the organisms that were living at that time are still preserved in the sedimentary layers of the seafloor. They are one of our most important archives for warm climate conditions, but as we have seen, we decoded them wrongly in the past," says Thomas Laepple.

科學家利用溫度指標 TEX86的數據來估算當時氣溫。這個縮寫代表由古菌產生的特定數種有機化合物之間的比例，其數值會跟它們生長時的水溫有關。「古菌是一種單細胞生物，其中某些種類可以忍受十分驚人的高溫。生存於當時的這些生物製造的分子至今仍保存在海床沉積物當中。它們是我們用來指出溫暖氣候的最重要紀錄之一，但現在我們了解到，之前我們都誤解了它們的含意。」 Thomas Laepple說。

He and his AWI colleague at the time, Sze Ling Ho, first had doubts about the interpretation of the TEX86 temperature indicator during a comparison of climate data from the most recent ice age. The scientists noticed that the TEX86 temperatures were far too cold compared to other geological evidence. "The discrepancy was so obvious that we started to review the TEX86 values of around 3,000 sediment samples from different ocean basins and from different epochs of the Earth. It soon became apparent that the average temperature change inferred from TEX86 was exaggerated, always and on all time scales, by one and a half to two times. The temperature it showed for cold periods was much too cold and the one for warm periods was much too warm," explains geochemist Sze Ling Ho.

他和當時的同事 Sze Ling Ho在比對最近一次冰河期的氣候資料時，首度對TEX86溫度指標的涵義開始感到懷疑。這兩位科學家注意到TEX86指示的溫度跟其他地質證據相比低了許多。「這個差異是如此顯而易見，使我們開始重新審視將近3000筆不同地球歷史時代以及不同海盆沉積物樣品中的TEX86值。很快地，我們就發現所有時期從TEX86推論而出的溫度變化平均值，都明顯比其他指標放大了1.5到2倍。它所顯示的溫度在寒冷時期過於嚴酷；而在溫暖時期則太過炎熱。」地球化學家Sze Ling Ho如此解釋。

The cause of this pattern had to be of a fundamental nature, a suspicion that was confirmed upon closer analysis. "TEX86 had previously been interpreted as an indicator of sea surface temperature, in spite the fact that the archaea that produce TEX86 rarely directly live at the sea surface. Through the comparison with other climate archives, we have been able to constrain the depth in which the TEX86 signal is produced. We now assume that TEX86 represents the water temperature at a depth of up to 500 metres," Sze Ling Ho explains.

必然有相當基礎的原理可以解釋這種情形，而此猜想也經由更加詳細的分析得到證實。「TEX86以往被當成是海洋表面溫度的指標，儘管生成TEX86的古菌很少直接生存在海洋表面。經由比對其他氣候研究方面的文獻，我們可以界定出製造TEX86訊號的深度。現在，我們推測TEX86代表的水溫深度最深可達500公尺。」 Sze Ling Ho解釋。

At this water depth, the temperature difference between the tropical oceans and the polar seas is smaller than at the surface. This has direct consequences for climate reconstruction, since the information generated from the indicator is differently translated into temperature values. "In practice, the TEX86 extreme values need to be roughly halved in the climate reconstructions. Comparing the corrected temperatures with the models shows that they now reflect the climate of the Eocene in a realistic and physically consistent way," explains Thomas Laepple.

熱帶跟極區海洋之間於此深度的溫度差異較海洋表面小了許多。這在重建氣候時會帶來直接影響，因為從TEX86指標得到的資訊會被轉化成不同數值的溫度。「實際上，重建氣候時必須要將TEX86呈現出的極端數值折半才行。溫度修正後的氣候模型跟之前相比，現在反映出的始新世氣候更加真實且較符合物理法則。」Thomas Laepple這麼解釋。

However, we also have to correct our temperature-conception of the Eocene. Thomas Laepple: "The era remains the warmest period of the past 65 million years. The water temperatures that we assumed for the Arctic and Antarctica, though, were overstated by at least ten degrees Celsius. Now, we know that the water in the Southern Ocean had a temperature of about 20 to 25 degrees Celsius at that time. The region was therefore still warm enough for there to be palm trees sprouting on the beach."

然而，我們對始新世時的氣溫概念也要有所修正。 Thomas Laepple說：「雖然我們之前對南北極的海水溫度至少高估了10℃以上，這仍然是過去6500萬年以來最溫暖的時期。現在我們得知當時南大洋的海水溫度約莫是20至25℃。因此這個區域仍然溫暖到足以使棕櫚樹在沙灘上繁茂生長。」

引用自：Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. "Long-awaited breakthrough in the reconstruction of warm climate phases." ScienceDaily. ScienceDaily, 18 July 2016.