挖洞：烏龜有甲殼的真正理由

Real reason turtles have shells: Burrowing tool

挖洞：烏龜有甲殼的真正理由

Dr. Tyler Lyson co-authors paper about turtle shells as a burrowing tool, not for protection as previously thought

Tyler Lyson博士參與在內的論文認為烏龜演化出甲殼是用來當作挖洞工具，而非先前認為的是為了保護自身

It is common knowledge that the modern turtle shell is largely used for protection. No other living vertebrate has so drastically altered its body to form such an impenetrable protective structure as the turtle. However, a new study by an international group of paleontologists suggests that the broad ribbed proto shell on the earliest partially shelled fossil turtles was initially an adaptation, for burrowing underground, not for protection. Paleontologist Tyler Lyson from the Denver Museum of Nature & Science is among the scientists that helped make this discovery.

眾所皆知現今烏龜的甲殼大多是用來保護自己。現存脊椎動物中沒有別的動物會像烏龜一樣劇烈改變自己的身體構造，來形成一道堅不可摧的防護性結構。然而，由一組國際古生物學家團隊進行的新研究表示，在僅有部分甲殼的最早龜類化石身上，由肋骨加寬形成的原始甲殼最初是為了挖地洞而出現的適應性構造，並非用來保護身體。丹佛自然科學博物館的古生物學家 Tyler Lyson是協助這項發現的其中一名科學家。

"Why the turtle shell evolved is a very Dr. Seuss-like question and the answer seems pretty obvious -- it was for protection," said Dr. Lyson, lead author of Fossorial Origin of the Turtle Shell, which was released today by Current Biology. But just like the bird feather did not initially evolve for flight, the earliest beginnings of the turtle shell was not for protection but rather for digging underground to escape the harsh South African environment where these early proto turtles lived."

「『烏龜為什麼會演化出甲殼？』是一則很有蘇斯博士(Dr. Seuss)風格的問題。而答案似乎顯而易見—為了保護自己。」論文《龜類甲殼的化石起源》的第一作者 Lyson博士說。此篇論文今日刊登於期刊《當代生物學》(Current Biology)之上。「但是，就像鳥類羽毛演化的最初目的並未是為了飛行，龜類甲殼最一開始也不是為了保護身體，而是生活於南非的原始龜類用來挖地洞以躲避牠們居住的嚴酷環境。」

The early evolution of the turtle shell had long puzzled scientists. "We knew from both the fossil record and observing how the turtle shell develops in modern turtles that one of the first major changes toward a shell was the broadening of the ribs," said Dr. Lyson. While distinctly broadened ribs may not seem like a significant modification, it has a serious impact on both breathing and speed in quadrupedal animals. Ribs are used to support the body during locomotion and play a crucial role in ventilating the lungs. Distinctly broadened ribs stiffen the torso, which shortens an animals stride length and slows it down, interfering with breathing.

烏龜甲殼的最初演化目的已經困擾科學家許久。「經由化石紀錄以及觀察現今龜類甲殼如何發育，我們了解到形成甲殼最重要的一步是拓寬肋骨。」 Lyson博士說。雖然拓寬肋骨單獨來看並不是很重大的變化，然而對四足動物而言這會重重影響牠們的呼吸過程和行走速度。肋骨除了在移動時用來支撐身體之外，在肺部空氣循環過程中也佔有一席之地。單單加寬肋骨會讓軀幹變得比較不靈活，造成動物的步幅縮短而減慢移動速度，也會影響牠們的呼吸過程。

"The integral role of ribs in both locomotion and breathing is likely why we don't see much variation in the shape of ribs," said Dr. Lyson. "Ribs are generally pretty boring bones. The ribs of whales, snakes, dinosaurs, humans, and pretty much all other animals look the same. Turtles are the one exception, where they are highly modified to form the majority of the shell."

「肋骨在運動過程和呼吸作用上皆具有相當重要的地位，這可能是我們在不同動物身上很少看到肋骨型態有重大變化的原因。」Lyson博士說。「肋骨一般來說是種相當無趣的骨頭。鯨魚、蛇、恐龍、人類以及其他大部分動物的肋骨看起來沒什麼不同。烏龜是其中一種例外，牠們將肋骨大幅改造成甲殼的主體架構。」

A big breakthrough came with the discovery of several specimens of the oldest (260- million-year-old) partially shelled proto turtle, Eunotosaurusafricanus, from the Karoo Basin of South Africa. Several of these specimens were discovered by two of the study's coauthors, Drs. Roger Smith and Bruce Rubidge from the University of Witwatersrand in Johannesburg. But the most important specimen was found by a then 8-year-old South African boy on his father's farm in the Western Cape of South Africa. This specimen, which is about 15 cm long, comprises a well preserved skeleton together with the fully articulated hands and feet.

這項重大突破來自於從南非卡魯盆地(Karoo Basin)中挖掘出來的數具最原始龜類之一(年代為2億6000萬年前)，非洲正南龜(Eunotosaurusafricanus)的化石，牠們已經具有部分甲殼。這些樣本其中幾具是由本研究的兩位共同作者，約翰尼斯堡金山大學的 Roger Smith和Bruce Rubidge博士發現。但最重要的一枚樣本是於南非西開普省由一位8歲南非男孩在他父親的農場上發現的。這具大約15公分長的樣品不但骨骸保存情況良好，就連手腳各關節也都完美地保存下來。

"I want to thank Kobus Snyman and shake his hand because without Kobus both finding the specimen and taking it to his local museum, the Fransie Pienaar Museum in Prince Albert, this study would not have been possible," said Dr. Lyson.

「我想跟Kobus Snyman好好地握手道謝。若Kobus沒有發現這具樣品並且將它帶到當地位於艾伯特親王鎮的 Fransie Pienaar 博物館，那這項研究就不可能完成。」Lyson博士說。

Denver Museum of Nature & Science. "Real reason turtles have shells: Burrowing tool: Dr. Tyler Lyson co-authors paper about turtle shells as a burrowing tool, not for protection as previously thought." ScienceDaily. ScienceDaily, 15 July 2016. <www.sciencedaily.com/releases/2016/07/160715171312.htm>.

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>.

苔蘚造成的岩石風化作用或許可以解釋發生於奧陶紀晚期的氣候現象

原文網址：www.sciencedaily.com/releases/2016/07/160707101029.htm

Weathering of rocks by mosses may explain climate effects during the Late Ordovician

苔蘚造成的岩石風化作用或許可以解釋發生於奧陶紀晚期的氣候現象

During the Ordovician period, the concentration of CO2 in Earth's atmosphere was about eight times higher than today. It has been hard to explain why the climate cooled and why the Ordovician glaciations took place. A new study, published in Nature Communications, shows that the weathering of rock caused by early non-vascular plants had the potential to cause such a global cooling effect.

奧陶紀時地球大氣二氧化碳的濃度是現在的八倍左右。因此很難解釋為何當時氣候會逐漸變冷以及奧陶紀冰河期的發生。刊登於期刊《自然通訊》(Nature Communications)的新研究顯示早期非維管束植物造成的岩石風化作用可能是全球冷化效應的成因。

"When we can better understand the carbon cycle in the past, we can better predict what happens with the climate in the future," says Philipp Porada of Stockholm University, one of the authors of the study.

「當我們對過去的碳循環有更加透徹的了解，我們就能更加準確地預測未來氣候會發生的變化。」本篇研究作者之一，斯德哥爾摩大學的 Philipp Porada說。

Non-vascular plants, such as mosses, hornworts and liverworts, probably evolved during the Ordovician period, around 450 million years ago. They are older than vascular plants, such as trees and grasses, and together with lichens, which are a symbiosis of fungi and algae, they formed the earliest terrestrial vegetation. Today's successors of these organisms are distributed worldwide and are characterised by their ability to survive in environments in which the supply of both water and nutrients is scarce. They are found in both cold and warm desert regions and are able to grow on rock surfaces and the bark of trees. Although they do not have real roots, they affect the surfaces on which they grow: the release of various organic acids dissolves underlying rock minerals.

非維管束植物，像是苔蘚、角苔和地錢可能是在4億5000萬年前左右的奧陶紀演化出來。其歷史早於樹木與花草這類的維管束植物許久，並且跟地衣(真菌和藻類的共生體)一起組成了最原始的陸上植被。今日在世界各地都有這些生物後代的蹤跡，並以能夠生活在水分及養分供應皆相當匱乏的環境聞名。它們可以存活於寒冷和炎熱的荒漠地區，也能生長在岩石表面及樹皮表層。雖然缺乏真正的根系，它們卻有方法影響它們生存的表面。它們可以分泌出各種有機酸來溶解下方岩石含有的礦物。

This process of dissolution and chemical transformation of rock minerals is called chemical weathering. Non-vascular plants and lichens may considerably increase weathering rates of the rock surfaces on which they grow. This has important implications for the climate system, since chemical weathering of silicate rocks such as granite results in a drawdown of atmospheric CO2 and may therefore lead to global cooling. During the weathering process CO2 dissolves in water as acid, and is then transported to the ocean where the carbon is buried as carbonate rock. Consequently, it has been hypothesised that early non-vascular vegetation caused an interval of glaciations at the end of the Ordovician period, when they became globally abundant. Without the drawdown of atmospheric CO2 caused by the enhancement of weathering rates, the Ordovician glaciations are hard to explain, since they started under conditions of eight times higher atmospheric CO2 than today.

岩石含有的礦物溶解且化學成分改變的過程稱作化學風化。非維管束植物和地衣或許能夠大幅增加它們生長的岩石表面的風化速率。這對氣候系統來說具有相當重大的意義，因為像花崗岩這類的矽酸岩發生化學風化時會減少大氣中的二氧化碳，而可能造成全球冷化。在風化過程中二氧化碳會以酸的形式溶解在水裡，接著被運輸至海洋，在此碳會形成碳酸鹽並埋藏在海底。因此，有項假說認為奧陶紀末期出現的冰河期，便是發生於當這些早期非維管束植物在全球數量大為增加之後。由於奧陶紀開始時大氣二氧化碳濃度是當今的八倍左右，因此若沒有風化速率增加導致的大氣二氧化碳含量下降，奧陶紀冰河期的成因便相當難以解釋。

"I believe that the most interesting thing about the study is that tiny plants such as mosses and lichens can influence global climate in the long run," says Philipp Porada.

「我認為這項研究中最有趣的部分是像苔蘚和地衣這般矮小的植物，長期而言卻能夠影響全球氣候。」 Philipp Porada說。

"However, it is difficult to extrapolate today's weathering rates by non-vascular plants and lichens measured in the field to a global effect on chemical weathering in the Ordovician. In our study we therefore use a process-based numerical model of non-vascular vegetation to simulate weathering by these organisms in the Late Ordovician. We find a high potential for weathering, which means that the emergence of early non-vascular plants and lichens indeed may have been the reason for the Late Ordovician glaciations."

「然而，要將今日在野外測得由非維管束植物和地衣導致的風化速率，外推至在奧陶紀時此效應對全球化學風化的影響是相當困難的。因此，在我們的研究當中，利用了一種基於過程的非維管束植物數值模型來模擬奧陶紀晚期時這些生物造成的風化作用。我們發現它們對風化作用可能具有相當大的影響，代表早期維管束植物跟地衣的出現確實有可能是晚奧陶紀冰河期的成因。」

引用自：Stockholm University. "Weathering of rocks by mosses may explain climate effects during the Late Ordovician." ScienceDaily. ScienceDaily, 7 July 2016. 

新研究顛覆地函流動理論

原文網址：www.sciencedaily.com/releases/2016/07/160706174225.htm

New study upends a theory of how Earth's mantle flows

新研究顛覆地函流動理論

Small-scale processes may have big effects

尺度微小的作用可能具有重大影響

A new study carried out on the floor of Pacific Ocean provides the most detailed view yet of how the earth's mantle flows beneath the ocean's tectonic plates. The findings, published in the journal Nature, appear to upend a common belief that the strongest deformation in the mantle is controlled by large-scale movement of the plates. Instead, the highest resolution imaging yet reveals smaller-scale processes at work that have more powerful effects.

於太平洋海床進行的新研究給出了關於地函在海洋板塊下方如何流動至今為主最詳細的觀察結果。出版在期刊《自然》(Nature)的這篇研究似乎顛覆了廣為接受的理論中，認為地函內部最劇烈的變形活動受控於大尺度板塊運動。反之，迄今解析度最高的影像透露出正在運行的小尺度作用具有更大的影響力。

By developing a better picture of the underlying engine of plate tectonics, scientists hope to gain a better understanding of the mechanisms that drive plate movement and influence related process, including those involving earthquakes and volcanoes.

科學家藉由發展出可以詳細觀測位於板塊運動下方的引擎如何運作，盼望能更加瞭解驅使板塊運動的機制，及其他像火山和地震的相關作用如何受其影響。

When we look out at the earth, we see its rigid crust, a relatively thin layer of rock that makes up the continents and the ocean floor. The crust sits on tectonic plates that move slowly over time in a layer called the lithosphere. At the bottom of the plates, some 80 to 100 kilometers below the surface, the asthenosphere begins. Earth's interior flows more easily in the asthenosphere, and convection here is believed to help drive plate tectonics, but how exactly that happens and what the boundary between the lithosphere and asthenosphere looks like isn't clear.

當我們注視地球時看到的是她堅硬的外殼，這個相對來說薄薄的一層岩石組成了陸地和海床。地殼坐落於「岩石圈」(lithosphere)中會隨著時間緩緩移動的板塊之上。而在板塊底部，位於地表之下大致深80至100公里處則會開始進入「軟流圈」(asthenosphere)。地球內部的岩石於軟流圈可以輕易地產生流動，一般據信此處發生的對流作用有助於驅動板塊構造作用進行。然而，確切來說這如何發生以及岩石圈跟軟流圈之間的邊界為何，仍然不太清楚。

To take a closer look at these processes, a team led by scientists from Columbia University's Lamont-Doherty Earth Observatory installed an array of seismometers on the floor of the Pacific Ocean, near the center of the Pacific Plate. By recording seismic waves generated by earthquakes, they were able to look deep inside the earth and create images of the mantle's flow, similar to the way a doctor images a broken bone.

為了更仔細地觀測這些作用如何進行，由哥倫比亞大學拉蒙特-多爾蒂地球觀測所( Lamont-Doherty Earth Observatory)的科學家領導的研究團隊，在接近太平洋板塊中心處的太平洋底安裝了一組地震儀觀測網。透過記錄地震產生的震波，他們可以看進地球深處並且繪製出地函流動的圖像，這跟醫生對骨折部位製作顯影的方法頗為相似。

Seismic waves move faster through flowing rock because the pressure deforms the crystals of olivine, a mineral common in the mantle, and stretches them in the same direction. By looking for faster seismic wave movement, scientists can map where the mantle is flowing today and where it has flowed in the past.

地震波在流動的岩石中會以較快的速度傳播，這是因為壓力會使橄欖石(olivine)這種地函中常見的礦物變形，並將它們往同樣方向延展。經由尋找地震波傳播速度較快的地方，科學家可以標示出今日地函有哪些部分正在流動，而哪些地方則在從前曾經流動過。

Three basic forces are believed to drive oceanic plate movement: plates are "pushed" away from mid-ocean ridges as new sea floor forms; plates are "pulled" as the oldest parts of the plate dive back into the earth at subduction zones; and convection within the asthenosphere helps ferry the plates along. If the dominant flow in the asthenosphere resulted solely from "ridge push" or "plate pull," then the crystals just below the plate should align with the plate's movement. The study finds, however, that the direction of the crystals doesn't correlate with the apparent plate motion at any depth in the asthenosphere. Instead, the alignment of the crystals is strongest near the top of the lithosphere where new sea floor forms, weakest near the base of the plate, and then peaks in strength again about 250 kilometers below the surface, deep in the asthenosphere.

一般認為有三種基本作用力驅動了板塊運動：首先是中洋脊產生新生海床時會把板塊往外「推離」；接著是板塊最古老部分在隱沒帶潛回地球內部時會「拉扯」板塊；而軟流圈中的對流作用則能協助這條輸送帶運作。如果軟流圈內部的主要流向僅由「洋脊推動」(ridge push)以及「板塊隱沒拉力」(plate pull)決定，那板塊正下方的晶體應該會順著板塊運動方向排列。然而，此篇研究卻發現不管在軟流圈中哪個深度，晶體排列方向跟現在的板塊運動方向之間皆沒有相關性。反之，晶體排列在岩石圈表層新生海床形成處附近最為一致，而在板塊最底部則最為凌亂，接著在軟流圈底部距地表約250公里深處，晶體排列一致度又達到高峰。

"If the main flow were the mantle being sheared by the plate above it, where the plate is just dragging everything with it, we would predict a fast direction that's different than what we see," said coauthor James Gaherty, a geophysicist at Lamont-Doherty. "Our data suggest that there are two other processes in the mantle that are stronger: one, the asthenosphere is clearly flowing on its own, but it's deeper and smaller scale; and, two, seafloor spreading at the ridge produces a very strong lithospheric fabric that cannot be ignored." Shearing probably does happen at the plate boundary, Gaherty said, but it is substantially weaker.

「假設地函流動的主要方向是由上方板塊整個拖曳時產生的剪力決定，基於此理論預測出的波速較快方向跟我們觀測到的並不一致。」共同作者，拉蒙特-多爾蒂的地球物理學家 James Gaherty說。「我們的數據顯示在地函內部還有兩種更加強勢的作用。第一，我們清楚看見軟流圈有自己的獨立流動模式，但這發生在軟流圈較深處且規模較小。第二，於中洋脊海床擴張時會產生不容小覷，相當明顯的岩石圈結構。」在板塊跟軟流圈邊界確實會發生剪動作用，但大體上其影響力並不足，Gaherty 說。

Donald Forsyth, a marine geophysicist at Brown University who was not involved in the new study, said, "These new results will force reconsideration of prevailing models of flow in the oceanic mantle."

並未參與此研究的布朗大學海洋地球物理學家Donald Forsyth說：「這些新發表的成果將會迫使我們重新審視現行的海洋地函流動模型。」

Looking at the entire upper mantle, the scientists found that the most powerful process causing rocks to flow happens in the upper part of the lithosphere as new sea floor is created at a mid-ocean ridge. As molten rock rises, only a fraction of the flowing rock squeezes up to the ridge. On either side, the pressure bends the excess rock 90 degrees so it pushes into the lithosphere parallel to the bottom of the crust. The flow solidifies as it cools, creating a record of sea floor spreading over millions of years.

綜觀整個上部地函，科學家發現使岩石圈上層岩石流動最有力的作用，來自於中洋脊生成新生海洋板塊時。當熔融岩石上湧時，流動的岩石中只有一部分會被擠出中洋脊。其餘岩石在壓力作用下會往兩側彎折90度，而被推進岩石圈內部並平行於地殼底部流動。這些流動的岩石會逐漸冷卻而凝固，形成經過數百萬年後仍能留存的海底擴張紀錄。

This "corner flow" process was known, but the study brings it into greater focus, showing that it deforms the rock crystals to a depth of at least 50 kilometers into the lithosphere.

這種「角落流」(corner flow)作用雖然早已為人所知，但此篇研究對它著墨甚多，認為這種使岩石圈的岩石晶體發生變形的作用範圍至少可以深達50公里處。

In the asthenosphere, the patterns suggest two potential flow scenarios, both providing evidence of convection channels that bottom out about 250 to 300 kilometers below the earth's surface. In one scenario, differences in pressure drive the flow like squeezing toothpaste from a tube, causing rocks to flow east-to-west or west-to-east within the channel. The pressure difference could be caused by hot, partially molten rock piled up beneath mid-ocean ridges or beneath the cooling plates diving into the earth at subduction zones, the authors write. Another possible scenario is that small-scale convection is taking place within the channel as chunks of mantle cool and sink. High-resolution gravity measurements show changes over relatively small distances that could reflect small-scale convection.

在流軟圈中的波速分布模式顯示有兩種可能的流動模式，都可以解釋軟流圈底層距地表深約250至300公里處的地函對流。在第一種模式中，壓力差導致流動發生的方式就像將牙膏擠出軟管一樣，造成岩石往西至東或往東至西流動。作者寫說壓力差會產生是因為熾熱的部分熔融岩石堆積在中洋脊之下，或者是累積在隱沒帶沉入地球深處的冷卻板塊下方。另一種模式則是當地函塊體冷卻並下沉時產生的小尺度對流。高解析度重力探測影像顯示相對短距離中發生的重力變化反映了小尺度對流的發生。

"The fact that we observe smaller-scale processes that dominate upper-mantle deformation, that's a big step forward. But it still leaves uncertain what those flow processes are. We need a wider set of observations from other regions," Gaherty said.

「我們觀察到小尺度作用主導了上部地函的變形作用，這可說是一大邁進。但詳細的流動過程仍然有不清楚的地方。我們還需要更多從其他地區得到的觀測資料。」Gaherty 說。

The study is part of the NoMelt project, which was designed to explore the lithosphere-asthenosphere boundary at the center of an oceanic plate, far from the influence of melting at the ridge. The scientists believe the findings here are representative of the Pacific Basin and likely ocean basins around the world.

這項研究是 NoMelt計畫的一部分，其目的是要於海洋板塊中央，遠離洋脊融熔物質影響的環境中來探索岩石圈—軟流圈的交界。科學家認為這裡的發現可以代表整個太平洋海盆以及世界各處的其他相似海盆。

NoMelt is unique because of its location. Most studies use land-based seismometers at edge of the ocean that tend to highlight the motion of the plates over the asthenosphere because of its large scale and miss the smaller-scale processes. NoMelt's ocean bottom seismometer array, with the assistance of Lamont's seismic research ship the Marcus G. Langseth, recorded data from earthquakes and other seismic sources from the middle of the plate over the span of a year.

NoMelt的獨特之處在於它的研究地點。多數研究利用架設在海洋邊緣的陸上地震儀觀測網得到的資訊，通常因為軟流圈驅動的板塊運動尺度較大而著重於此，但卻忽略了小尺度作用。NoMelt的海底地震儀觀測網在拉蒙特-多爾蒂的研究船 Marcus G. Langseth號的協助下，可以記錄數年之間發生在板塊中央的地震以及其他震波來源產生的數據。

引用自：Lamont-Doherty Earth Observatory, Columbia University. "New study upends a theory of how Earth's mantle flows: Small-scale processes may have big effects." ScienceDaily. ScienceDaily, 6 July 2016. 

順暢無阻的板塊運動：發生在超慢速中洋脊的地震詳細記錄

原文網址：www.sciencedaily.com/releases/2016/06/160629135238.htm

Plate tectonics without jerking: Detailed recordings of earthquakes on ultraslow mid-ocean ridges

順暢無阻的板塊運動：發生在超慢速中洋脊的地震詳細記錄

The earthquake distribution on ultraslow mid-ocean ridges differs fundamentally from other spreading zones. Water circulating at a depth of up to 15 kilometres leads to the formation of rock that resembles soft soap. This is how the continental plates on ultraslow mid-ocean ridges may move without jerking, while the same process in other regions leads to many minor earthquakes, according to geophysicists of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). Their stultraslow mid-ocean ridgeudy is going to be published advanced online in the journal Nature on Wednesday, June 29, 2016.

在超慢速中洋脊(ultraslow mid-ocean ridge)發生的地震其分佈模式相較於其他擴張帶有著根本上的差異。此處的水可以循環至地下15公里深處，而形成跟軟皂十分相似的岩石。根據阿爾弗雷德•韋格納暨亥姆霍茲極地與海洋研究所的地球物理學家表示，這便是超慢速中洋脊上的大陸板塊可以順暢無阻地移動，然而同樣過程在其他中洋脊卻會產生許多小地震的原因。他們的研究將會於2016/6/29預先刊登在期刊《自然》(Nature)的線上版。

Mountain ranges like the Himalayas rise up where continental plates collide. Mid-ocean ridges, where the continents drift apart, are just as spectacular mountain ranges, but they are hidden in the depths of the oceans. On the seabed, like on a conveyor belt, new ocean floor (oceanic lithosphere) is formed as magma rises from greater depths to the top, thus filling the resulting gap between the lithospheric plates. This spreading process creates jerks, and small earthquakes continuously occur along the conveyor belt. The earthquakes reveal a great deal about the origin and structure of the new oceanic lithosphere. On the so-called ultraslow ridges, the lithospheric plates drift apart so slowly that the conveyor belt jerks and stutters and, because of the low temperature, there is insufficient melt to fill the gap between the plates. This way, the earth's mantle is conveyed to the seabed in many places without earth crust developing. In other locations along this ridge, on the other hand, you find giant volcanoes.

當大陸板塊碰撞時會隆起像喜馬拉雅山這類的宏偉山脈。中洋脊身為陸地彼此漂離之處雖然也跟山脈同樣壯觀，但它們卻隱藏在海洋深處。海底就像輸送帶一樣，當岩漿從地球深處往上湧至地表，因而填補板塊岩石圈之間的間隙時，就會形成新的海床(海洋岩石圈)。此種擴張過程會產生顫動，使輸送帶周邊不斷發生小地震，這些地震會透露跟新的海洋岩石圈來源和構造有關的大量訊息。在所謂的「超慢速中洋脊」(ultraslow ridge)板塊岩石圈漂離的速度相當慢，使得輸送帶僅能斷斷續續地運作。且因為此處溫度相對較低造成融熔物質的量不足以填滿板塊之間的空隙，使得此區域中有許多地方的地函到達海床時並未伴隨新地殼形成。另一方面，在此種洋脊的其他地方則可以發現許多巨型火山。

Ultraslow ridges can be found under the sea ice in the Arctic and south of Africa along the Southwest Indian Ridge in the notorious sea areas of the Roaring Forties and Furious Fifties. Because these areas are so difficult to access, earthquakes have not been measured there. And so until now, little was known about the structure and development of around 20 percent of the global seabed.

在南極海的海冰之下以及沿著西南印度洋海脊可以發現超慢速中洋脊。西南印度洋海域因為「咆哮四十度及瘋狂五十度」(Roaring Forties and Furious Fifties)而惡名昭彰。由於這些區域相當難以抵達，使得此處的地震活動尚未有人觀測，也造成全球海床約20%的區域其構造和發育到目前為止仍所知甚少。

With the research vessel Polarstern, a reliable workhorse even in heavy seas, the researchers around Dr Vera Schlindwein of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have now for the first time risked deploying a network of ocean bottom seismometers (OBS) at the Southwest Indian Ridge in the Furious Fifties and recovered them a year later. At the same time, a second network was placed on a volcano in the more temperate latitudes of the Southwest Indian Ridge. "Our effort and our risk were rewarded with a unique set of earthquake data, which for the first time provides deep insights into the formation of the ocean floor when spreading rates are very slow," explains AWI geophysicist Vera Schlindwein.

今日，藉著即使在波濤洶湧的海域依然能良好運作的研究船「 Polarstern」，以阿爾弗雷德•韋格納暨亥姆霍茲極地與海洋研究所(AWI)的 Vera Schlindwein博士為首的研究人員，首度能冒險去西南印度洋海脊於咆哮四十度及瘋狂五十度的海域架設海底地震儀(OBS)觀測網，並在一年之後回收這些儀器。於此同時，第二個觀測網則設立在西南印度洋海脊較接近中緯度的一座火山之上。「這些獨一無二的地震數據讓我們首度有機會能仔細探究板塊擴張速率十分緩慢的情況下海床會如何形成，花費於此的心力和冒的風險可說是相當值得。」AWI的地球物理學家 Vera Schlindwein如此解釋。

Her results turn current scientific findings on the functioning of ultra-slow mid-ocean ridges upside down: Schlindwein and her PhD student Florian Schmid found that water may circulate up to 15 kilometres deep in the young oceanic lithosphere, i.e. the earth crust and the outer part of the earth mantle. If this water comes into contact with rock from the earth mantle, a greenish rock called serpentinite forms. Even small quantities of ten percent serpentinite are enough for the rock to move without any earthquakes as if on a soapy track. The researchers discovered such aseismic areas, clearly confined by many small earthquakes, in their data.

她的結果徹底顛覆了目前對超慢速中洋脊運作方式的科學認知：Schlindwein和她的博士生Florian Schmid發現這裡的海水可以循環滲透至年輕海洋岩石圈15公里深之處，也就是整個幼年地殼及地函外圍。如果海水跟地函岩石接觸，就會形成一種稱作蛇紋岩(serpentinite)的綠色岩石。即使蛇紋岩含量僅有少少的10%，也足以讓岩石移動時不發生地震，如同在滑溜的道路上前進一般。研究人員從他們的數據中發現這種無震帶清楚地被包夾在許多小型地震之間。

Until now, scientists thought that serpentinite only forms near fault zones and near the surface. "Our data now suggest that water circulates through extensive areas of the young oceanic lithosphere and is bound in the rock. This releases heat and methane, for example, to a degree not previously foreseen," says Vera Schlindwein.

科學家迄今認為蛇紋岩只會形成於斷層帶周遭接近地表處。「從數據看來，我們現在認為水可以循環至年輕海洋岩石圈中許多區域並且跟岩石互相結合。這個過程會釋放出像是熱能及甲烷的物質，其量之大可能遠超出我們的預期。」Vera Schlindwein說。

The AWI geophysicists were now able to directly observe the active spreading processes using the ocean floor seismometers, comparing volcanic and non-volcanic ridge sections. "Based on the distribution of earthquakes, we are for the first time able to watch, so to speak, as new lithosphere forms with very slow spreading rates. We have not had such a data set from ultra-slow ridges before," says Vera Schlindwein.

如今，這位AWI的地球物理學家利用海底地震儀可以直接觀測正在發生的擴張過程，並且可以比較洋脊中有火山活動跟沒有的區段之間的差異。「我們根據地震的分布情況首度能『監看』在極度緩慢的擴張速率下新生岩石圈的形成過程。在這之前我們從未自超慢速洋脊得到這樣的數據。」

"Initially, we were very surprised that areas without earth crust show no earthquakes at all down to 15 kilometres depth, even though OBS were positioned directly above. At greater depths and in the adjacent volcanic areas, on the other hand, where you can find basalt on the sea floor and a thin earth crust is present, there were flurries of quakes in all depth ranges," says Vera Schlindwein about her first glance at the data after retrieving the OBS with RV Polarstern in 2014.

「起初我們發現即使直接於地殼不存在的區域上方架設海底地震儀，直到地下15公里深都沒有偵測到地震發生，這讓我們十分訝異。另一方面，在鄰近海床上有玄武岩及薄層地殼覆蓋的火山帶以及更深的區域，在各個深度地震都毫不停歇地發生。」Vera Schlindwein如此描述她於2014年藉由Polarstern研究船取回海底地震儀後，對其中所含數據的最初觀察結果。

The results also have an influence on other marine research disciplines: geologists think about other deformation mechanisms of the young oceanic lithosphere. Because rock that behaves like soft soap permits a completely different deformation, which could be the basis of the so-called "smooth seafloor" that is only known from ultra-slow ridges. Oceanographers are interested in heat influx and trace gases in the water column in such areas, which were previously thought to be non-volcanic and "cold." Biologists are interested in the increased outflow of methane and sulphide on the sea floor that is to be expected in many areas and that represents an important basis of life for deep-sea organisms.

研究結果對於其他海洋科學研究領域也有相當影響。地質學家認為這是幼年海洋岩石圈的另一種變形機制。行為像軟皂的岩石可以讓一種截然不同的變形機制發生，這可能是形成僅在超慢速洋脊觀察到的「平滑海床」的基礎原理。過往海洋學家認為這個區域沒有火山活動發生且十分「寒冷」，現在他們則對當地水層的熱流量和稀有氣體相當感興趣。生物學家關注此研究預期許多區域海床上的甲烷和硫化物有較高的排放量，因為這些物質對深海生物來說是維持生命相當重要的基石。

引用自：Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. "Plate tectonics without jerking: Detailed recordings of earthquakes on ultraslow mid-ocean ridges." ScienceDaily. ScienceDaily, 29 June 2016. 

地球深處的巨大岩石團塊握有關於我們星球的重大資訊

原文網址：www.sciencedaily.com/releases/2016/06/160624155000.htm

Giant Blobs of Rock, Deep Inside the Earth, Hold Important Clues About Our Planet

地球深處的巨大岩石團塊握有關於我們星球的重大資訊

Two massive blob-like structures lie deep within Earth, roughly on opposite sides of the planet. The two structures, each the size of a continent and 100 times taller than Mount Everest, sit on the core, 1,800 miles deep, and about halfway to the center of Earth.

在地球深處有兩個巨大團塊狀構造，大致位於地球相對兩側。這兩個構造的大小都跟一個陸塊差不多，且厚度是聖母峰的100倍之上。它們位處距地表深1800哩(約2900公里)離地核不遠處，差不多是地表至地球中心距離的一半。

Arizona State University scientists Edward Garnero, Allen McNamara and Sang-Heon (Dan) Shim, of the School of Earth and Space Exploration, suggest these blobs are made of something different from the rest of Earth's mantle. The scientists' work appears in the June issue of Nature Geoscience.

亞利桑納州立大學地球與宇宙探索學院的科學家Edward Garnero、 Allen McNamara和Sang-Heon (Dan) Shim提出這些團塊是由跟地函其他部分截然不同的物質組成。這些科學家的研究成果刊登於六月號的《自然—地質科學》(Nature Geoscience)。

"While the origin and composition of the blobs are yet unknown," said Garnero, "we suspect they hold important clues as to how Earth was formed and how it works today."

「雖然這些團塊的成分和起源仍然不太清楚。」 Garnero說。「我們猜想它們握有地球如何形成以及地球現今如何運作的重大線索。」

The blobs, he says, may also help explain the plumbing that leads to some massive volcanic eruptions, as well as the mechanism of plate tectonics from the convection, or stirring, of the mantle. This is the geo-force that drives earthquakes.

他說這些團塊或許有助於解釋導致大型火山噴發的岩漿系統，以及地函對流或擾動藉由何種機制促成板塊構造運動。後者同時也是驅動地震發生的地質作用力。

Deep stirring

來自深層的擾動

Earth is layered like an onion, with a thin outer crust, a thick viscous mantle, a fluid outer core and a solid inner core. The two blobs sit in the mantle on top of Earth's core, under the Pacific Ocean on one side and beneath Africa and the Atlantic Ocean on the other.

地球就像洋蔥一樣可分成數層，最外面是薄薄的地殼，接著是又厚又黏稠的地函，最後則是液狀的外核和固態的內核。這兩個團塊位於地函中距地核不遠處，其中一個位於太平洋下方，另一個則在非洲和大西洋之下。

Waves from earthquakes passing through Earth's deep interior have revealed that these blobs are regions where seismic waves travel slowly. The mantle materials that surround these regions are thought to be composed of cooler rocks, associated with the downward movement of tectonic plates.

穿過地球深處的地震波顯示這些團塊是會讓地震波通過時減慢的區域。一般認為包圍這些區域的物質是由溫度較低，跟板塊下沉有關的岩石組成。

The blobs, also called thermochemical piles, have long been depicted as warmer-than-average mantle materials, pushed upward by a slow churning of hot mantle rock. The new paper argues they are also chemically different from the surrounding mantle rock, and may partly contain material pushed down by plate tectonics. They might even be material left over from Earth's formation, 4.5 billion years ago.

這些又稱作「熱化學堆」(thermochemical pile)的團塊長久以來被描述成溫度高於地函平均的物質，並且受炙熱地函岩石的攪動而往上湧。這篇新論文聲稱它們在化學性質上也跟周圍的地函岩石不同，並且含有一部分由板塊構造運動下推至此的物質。它們甚至可能是自地球45億年前形成時殘存至今的物質。

Much is yet to be learned about these blobs. But the emerging view from seismic and geodynamic information is that they appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and have been shaped by the mantle's large-scale flow. The scientists expect that further work on the two deep-seated anomalies will help clarify the picture and tell of their origin.

對於這些團塊還有很多尚待瞭解之處。但從地震學以及地球動力學得到的新觀點認為它們的密度跟周遭地函相較而言比較高，在動力學上則處於長期穩定的狀態，且形狀會受到地函大尺度流動的影響。科學家希冀未來對這兩個地球深處異常帶的研究可以幫助科學家闡明它們的樣貌和起源。

"If a neuroscientist found an unknown structure in the human brain, the whole community of brain scientists, from psychologists to surgeons, would actively pursue understanding its role in the function of the whole system," Garnero said.

「如果有位神經學家在人腦中找到一塊前所未知的區域，那整個腦科學界，從心理學家至外科醫生都會熱切地去瞭解這個新區域在整個系統當中扮演何種腳色。」 Garnero說。

"As the thermochemical piles come into sharper focus, we hope other Earth scientists will explore how these features fit into the big puzzle of planet Earth."

「隨著熱化學堆越來越受到注目，我們希望其他地球科學家來探索這些特殊構造應該嵌合在地球這幅大拼圖中的何處。」

引用自：Arizona State University (ASU). "Giant Blobs of Rock, Deep Inside the Earth, Hold Important Clues About Our Planet." ScienceDaily. ScienceDaily, 24 June 2016.