奧克拉荷馬州的地震與鑽探石油及天然氣有關

原文網址：http://www.sciencedaily.com/releases/2015/06/150618145809.htm

Oklahoma earthquakes linked to oil and gas drilling

奧克拉荷馬州的地震與鑽探石油及天然氣有關

Stanford geophysicists have identified the triggering mechanism responsible for the recent spike of earthquakes in parts of Oklahoma -- a crucial first step in eventually stopping them.

史丹佛大學的地球物理學家確認了最近發生於奧克拉荷馬州部分地區的頻繁地震的觸發機制為何--對遏止這種現象來說是重要的第一步。

In a new study published in the June 19 issue of the journal Science Advances, Professor Mark Zoback and PhD student Rall Walsh show that the state's rising number of earthquakes coincided with dramatic increases in the disposal of salty wastewater into the Arbuckle formation, a 7,000-foot-deep, sedimentary formation under Oklahoma.

在刊登於6月19日的《科學前緣》(Science Advances)期刊的新研究當中，Mark Zoback教授與博士生Rall Walsh顯示此州的地震次數增加，與注入Arbuckle層的含鹽汙水劇增呈現一致的關係。Arbuckle層為奧克拉荷馬州7000呎之下的沉積岩層。

In addition, the pair showed that the primary source of the quake-triggering wastewater is not so-called "flow back water" generated after hydraulic fracturing operations. Rather, the culprit is "produced water"-brackish water that naturally coexists with oil and gas within the Earth. Companies separate produced water from extracted oil and gas and typically reinject it into deeper disposal wells.

此外，這對科學家顯示引發地震的汙水的主要來源並非由水力壓裂法產生，即一般所稱的「回水」(flow back water)。相反的，真兇是採出水(produced water)，為自然情形下在地球內部與油氣共存的水。石油公司從抽出的油氣中分離採出水後，一般會將其回注至更深的處置井(disposal well)中。

"What we've learned in this study is that the fluid injection responsible for most of the recent quakes in Oklahoma is due to production and subsequent injection of massive amounts of wastewater, and is unrelated to hydraulic fracturing," said Zoback, the Benjamin M. Page Professor in the School of Earth, Energy & Environmental Sciences.

「我們從這篇研究中學到的是，最近大部分奧克拉荷馬州的地震的引發機制，主要為將開採時產生的大量汙水回注至地下，而與水力壓裂法無關。」Zoback說，其為(史丹佛大學)地球、能源與環境科學系的Benjamin M. Page榮譽教授。

The Stanford study results were a major contributing factor in the recent decision by the Oklahoma Geological Survey (OGS) to issue a statement that said it was "very likely" that most of the state's recent earthquakes are due to the injection of produced water into disposal wells that extend down to, or even beyond, the Arbuckle formation.

奧克拉荷馬州地質調查局(OGS)最近決定發表的聲明中，主要基於這項史丹佛大學的研究結果，認為此州最近的大多數地震「相當有可能」是因為採出水被注入至深達Arbuckle層或甚至未達此深度的處置井所造成。

Recent increases in seismicity

近期增加的地震活動

Before 2008, Oklahoma experienced one or two magnitude 4 earthquakes per decade, but in 2014 alone, the state experienced 24 such seismic events. Although the earthquakes are felt throughout much of the state, they pose little danger to the public, but scientists say that the possibility of triggering larger, potentially damaging earthquakes cannot be discounted.

在2008年以前，奧克拉荷馬州每10年僅會發生1至2次規模4以上的地震，但單在2014年就發生了24次同等規模的事件。雖然全州都能感受到這些地震，它們並未對大眾造成危害，但科學家認為不能低估將來會發生更大型而具危險性的地震的可能性。

In the study, Zoback and Walsh looked at three study areas-centered around the towns of Cherokee, Perry and Jones-in Oklahoma that have experienced the greatest number of earthquakes in recent years. All three areas showed clear increases in quakes following increases in wastetwater disposal. Three nearby control areas that did not have much wastewater disposal did not experience increases in the number of quakes.

在本研究中，Zoback與Walsh觀察在奧克拉荷馬州分別以Cherokee、Perry及Jones這三個鎮附近為中心的研究區域。這些區域在近年來經歷了最多次的地震事件。在汙水處置量增加後，這三個區域的地震數量皆明顯上升。而在鄰近的三個汙水處置量不大，可視為控制組的區域，並沒有發生地震數目增加的現象。

Because the pair were also able to review data about the total amount of wastewater injected at wells, as well as the total amount of hydraulic fracturing happening in each study area, they were able to conclude that the bulk of the injected water was produced water generated using conventional oil extraction techniques, not during hydraulic fracturing.

由於他們也檢視了注入井中的汙水總量，以及每個地區水力壓裂法用量的相關數據，因此他們能夠總結，大部分注入井中的汙水是由一般萃取石油技術所產生的採出水，而非來自水力壓裂法。

"We know that some of the produced water came from wells that were hydraulically fractured, but in the three areas of most seismicity, over 95 percent of the wastewater disposal is produced water, not hydraulic fracturing flowback water," said Zoback, who is also a senior fellow at Stanford's Precourt Institute for Energy and director of the university's recently launched Natural Gas Initiative, which is focused on ensuring that natural gas is developed and used in ways that are economically, environmentally, and societally optimal.

「我們知道部分注入井裡的採出水來自水力壓裂法，但在那3個最多地震活動的區域，超過95%的處置汙水來自採出水，而非水力壓裂法的回流水，」Zoback說，他同時也是史丹佛皮考特能源研究所(Stanford's Precourt Institute for Energy)的高等研究員，以及史丹佛最近發起的天然氣計畫的領導人，其旨在確保天然氣的開發及使用符合經濟效益、環保與社會最適性。

Time delay explained

對時間差的解釋

The three study areas in Oklahoma that Zoback and Walsh looked at all showed a time delay between peak injection rate and the onset of seismicity, as well as spatial separations between the epicenter of the quakes and the injection well sites. Some of the quakes occurred months or even years after injection rates peaked and in locations that were sometimes located miles away from any wells.

Zoback與Walsh觀察位於奧克拉荷馬州的3個研究區域，發現注水速率的最高峰與地震活動的開始之間皆有時間差，而震央離注水井的廠址也有一段距離。某些地震發生在注水速率高峰後的數月甚至是數年之後，而發生位置也跟最近的井有數哩之遠。

These discrepancies had previously puzzled scientists, and had even been used by some to argue against a link between wastewater disposal and triggered earthquakes, but Zoback said they are easily explained by a simple conceptual model for Oklahoma's seismicity that his team has developed.

先前這些時空差讓科學家們感到十分疑惑，而某些人也以此來質疑汙水處置與地震之間的關聯性，但Zoback聲稱他們可以用其團隊發展的簡易概念模型，來輕鬆解釋奧克拉荷馬州的地震活動。

According to this model, wastewater disposal is increasing the pore pressure in the Arbuckle formation, the disposal zone that sits directly above the crystalline basement, the rock layer where earthquake faults lie. Pore pressure is the pressure of the fluids within the fractures and pore spaces of rocks at depth. The earth's crust contains many pre-existing faults, some of which are geologically active today. Shear stress builds up slowly on these faults over the course of geologic time, until it finally overcomes the frictional strength that keeps the two sides of a fault clamped together. When this happens, the fault slips, and energy is released as an earthquake.

Arbuckle層位在地震斷層所處的結晶岩盤正上方，根據此模型，注入至Arbuckle層的污水會增加其孔隙水壓。孔隙水壓為深處岩石中的裂縫與孔隙內的液體造成的壓力。地球的地殼當中有許多早已存在的斷層，在現今有些會發生地質活動。在漫長的地質時間中，剪應力會持續累積在那些斷層上，直到超過將斷層兩側嵌在一起的摩擦強度。當這種情況發生，斷層便會滑移，而能量就會以地震的形式釋放出來。

Active faults in Oklahoma might trigger an earthquake every few thousand years. However, by increasing the fluid pressure through disposal of wastewater into the Arbuckle formation in the three areas of concentrated seismicity-from about 20 million barrels per year in 1997 to about 400 million barrels per year in 2013-humans have sped up this process dramatically. "The earthquakes in Oklahoma would have happened eventually," Walsh said. "But by injecting water into the faults and pressurizing them, we've advanced the clock and made them occur today."

奧克拉荷馬州的活斷層大概每數千年就會發生一次地震。然而在那三個地震集中的地區，汙水處置注入Arbuckle層的液體量，從1997年的每年2千萬桶暴增至2013年的每年4億桶，造成孔隙水壓快速升高而劇烈加速了整個過程。「奧克拉荷馬州總有一天會發生地震，」 Walsh說。「但藉由將水注入至斷層中而對其施加壓力，我們撥快了時鐘而造成它們發生於今日。」

Moreover, because pressure from the wastewater injection is spreading throughout the Arbuckle formation, it can affect faults located far from well sites, creating the observed time delay. "You can easily imagine that if a fault wasn't located directly beneath a well, but several miles away, it would take time for the fluid pressure to propagate," Walsh said.

此外，由於汙水注入造成的壓力會擴散至整個Arbuckle 層，因此離井址很遠的斷層也會受到影響，這會造成我們觀測到的時間差。「你可以輕易想像若一斷層並非位在井的正下方，而是位於數哩遠的地方，則水壓要擴散至此斷層便需要一段時間。」Walsh說。

Possible solutions

可能的解決之道

Now that the source of the recent quakes in Oklahoma is known, scientists and regulators can work on ways to stop them. One possible solution, Zoback said, would be cease injection of produced water into the Arbuckle formation entirely, and instead inject it back into producing formations such as the Mississippian Lime, an oil-rich limestone layer where much of the produced water in Oklahoma comes from in the first place.

既然已經知曉近日發生於奧克拉荷馬州的地震成因，科學家與管理人員便能夠開始遏止它們。一個可能的解決方案，Walsh說，便是全面停止將採出水注入至Arbuckle層，而是回注至儲油層，像是密西西比石灰岩。密西西比石灰岩為含油豐富的石灰岩層，奧克拉荷馬州的採出水多半來自於此。

Some companies already reinject water back into reservoirs in order to displace remaining oil and make it easier to recover. The Stanford study found that this technique, called enhanced oil recovery, does not result in increased earthquakes.

某些企業已經開始將汙水重新注回儲油層，目的為用水置換其中剩餘的油使它們更容易被回收。史丹佛的這篇研究發現此種稱作「強化增產石油(enhanced oil recovery)」的技術，並不會造成地震增加。

Even if companies opt to use producing formations to store wastewater, however, the quakes won't cease immediately. "They've already injected so much water that the pressure is still spreading throughout the Arbuckle formation," Zoback said. "The earthquakes won't stop overnight, but they should subside over time."

即使企業已經選擇以儲油層作為汙水存放處，地震也不會立刻停止。「他們注入的水實在太多了，造成壓力仍在整個Arbuckle層中逐漸擴散，」Zoback說。「地震不會在一夜之間就此平息，但隨著時間流逝，它們終將沉寂。」

引用自：Stanford's School of Earth, Energy & Environmental Sciences. "Oklahoma earthquakes linked to oil and gas drilling." ScienceDaily. ScienceDaily, 18 June 2015. <www.sciencedaily.com/releases/2015/06/150618145809.htm>.

與尼安德塔人混血的早期現代人

原文網址：http://www.sciencedaily.com/releases/2015/06/150622122718.htm

Early modern humans interbred with Neanderthals

An early European had a close Neanderthal ancestor

與尼安德塔人混血的早期現代人

一位擁有尼安德塔近祖的早期歐洲人

Neanderthals became extinct about 40,000 years ago but contributed on average one to three percent to the genomes of present-day Eurasians. Researchers have now analyzed DNA from a 37,000 to 42,000-year-old human mandible from Oase Cave in Romania and have found that six to nine percent of this person's genome came from Neanderthals, more than any other human sequenced to date. Because large segments of this individual's chromosomes are of Neanderthal origin, a Neanderthal was among his ancestors as recently as four to six generations back in his family tree. This shows that some of the first modern humans that came to Europe mixed with the local Neanderthals.

雖然尼安德塔人在40,000年前就已經滅絕，但平均而言，現代歐洲人基因組的1%至3%來自於他們。研究人員分析發現於羅馬尼亞的Oase洞，年代約37,000至42,000年前的人類下顎骨中的DNA，發現此人的基因組中有6%至9%來自於尼安德塔人，比現今所有定序過的人類DNA都要多。由於他有來源為尼安德塔人的大片段染色體，因此觀其族譜，可能他的前4代至前6代祖先中就有一位是尼安德塔人。這顯示前往歐洲的第一批現代人類中，有一些曾與尼安德塔人通婚。

All present-day humans who have their roots outside sub-Saharan Africa carry one to three percent of Neanderthal DNA in their genomes. Until now, researchers have thought it most likely that early humans coming from Africa mixed with Neanderthals in the Middle East around 50,000 to 60,000 years ago, before spreading into Asia, Europe and the rest of the world. However, radiocarbon dating of remains from sites across Europe suggests that modern humans and Neanderthals both lived in Europe for up to 5,000 years and that they may have interbred there, too.

在所有祖先可以追溯至撒哈拉以南非洲之外的現代人來說，他們的基因組中會攜帶1%至3%來自尼安德塔人的DNA。目前為止，研究人員認為離開非洲的早期人類約在50,000至60,000年前，在中東與尼安德塔人混血，爾後才散佈至亞洲、歐洲與世界其他角落。然而，歐洲各地遺址中的骨骸的放射性碳定年結果顯示，現代人與尼安德塔人曾在歐洲共同生活達5,000年之久，因此他們也可能在歐洲混血。

In 2002, a 40,000-year-old jawbone was found by cavers in Oase Cave in south-western Romania and the site was subsequently studied by an international team led by the researchers of the Emil Racovita Institute of Speleology in Romania. Researchers from the Max Planck Institute for Evolutionary Anthropology (Germany), Harvard Medical School (USA), and the Key Laboratory of Vertebrate Evolution and Human Origins in Beijing (China) have now analyzed DNA from this fossil, which is one of the earliest modern-human remains found in Europe. They estimate that five to 11 percent of the genome preserved in the bone derives from a Neanderthal ancestor, including exceptionally large segments of some chromosomes. By estimating how lengths of DNA inherited from an ancestor shorten with each generation, the researchers estimated that the man had a Neanderthal ancestor in the previous four to six generations.

2002年，一些洞穴探索者在羅馬尼亞西南方的Oase洞發現一塊年代為40,000年的下顎骨，此遺址隨後由羅馬尼亞的埃米爾·拉科維澤洞穴學研究所(the Emil Racovita Institute of Speleology)的科學家所領導的國際團隊進行相關研究。馬克斯·普朗克演化人類學研究所(the Max Planck Institute for Evolutionary Anthropology，德國)、哈佛醫學院(Harvard Medical School，美國)與北京脊椎動物演化與人類起源重點實驗室(中國)的研究人員已完成這塊骨骸的DNA分析，其為在歐洲發現的現代人化石中，年代最古老的其中之一。他們估計這塊骨頭保存下來的基因組中有5%至11%來自他的一位尼安德塔人祖先，包括某些染色體中特別長的片段。藉由估算祖先留下來的DNA長度會如何隨著世代傳遞而縮減，研究人員估計這位男士的前4至6代中有一位尼安德塔人祖宗。

"The data from the jawbone imply that humans mixed with Neanderthals not just in the Middle East but in Europe as well" says Qiaomei Fu, one of the lead researchers of the study. "Interestingly, the Oase individual does not seem to have any direct descendants in Europe today," says David Reich from Harvard Medical School who coordinated the population genetic analyses of the study. "It may be that he was part of an early migration of modern humans to Europe that interacted closely with Neanderthals but eventually became extinct."

「從這塊下顎骨中得到的資料顯示，人類與尼安德塔人的混血不僅發生於中東，也會在歐洲發生。」其中一位主要研究人員付巧梅說。「有趣的是，在今日的歐洲似乎沒有這位Oase人的直系後裔。」來自哈佛醫學院，協助本研究的族群遺傳分析(population genetic analyse)的David Reich說。「他可能是早期移民至歐洲的現代人中，與尼安德塔人密切互動，但最終滅絕的族群中的其中一份子。」

"It is such a lucky and unexpected thing to get DNA from a person who was so closely related to a Neanderthal" comments Svante Paabo from the Max Planck Institute for Evolutionary Anthropology who led the study. "I could hardly believe it when we first saw the results." "We hope that DNA from other human fossils that predate the extinction of Neanderthals will help reconstruct the interactions between Neanderthals and modern humans in even more detail," says Mateja Hajdinjak, another key researcher involved in the study.

「能夠從一位與尼安德塔人關係親近的人身上取得DNA，完全是一件幸運至極且出乎意料的事。」領導本研究，來自馬克斯·普朗克演化人類學研究所的Svante Paabo評論。「第一眼看到結果時我們相當難以置信。」「我們希望其他年代為尼安德塔人絕種之前的人類化石中的DNA，可以幫助我們重建尼安德塔人與現代人間是如何互動的更多細節。」 參與本研究的另一位主要科學家，Mateja Hajdinjak說。

"When we started the work on Oase site, everything was already pointing to an exceptional discovery," remembers Oana Moldovan, the Romanian researcher who initiated the systematic excavation of the cave in 2003. "But such discoveries require painstaking research to be confirmed," adds Silviu Constantin, her colleague who worked on dating of the site. "We have previously shown that Oase is indeed the oldest modern human in Europe known so far, and now this research confirms that the individual had a Neanderthal ancestor. What more could we wish for?"

「當我們開始著手Oase遺址的考古工作時，所有跡象就已經指出這裡會有重大發現。」羅馬尼亞學者Oana Moldovan回憶道，她於2003年開始對此洞穴進行系統性的開挖。「但要證實這種大發現需要眾人辛勤的研究，」她的同事Silviu Constantin補充說，其研究為對此遺址進行定年。「我們之前已經顯示Oase確實是目前為止歐洲最古老的現代人，而現在本研究又確認了他有位尼安德塔人祖先。我們還能夠奢求什麼呢？」

引用自：Max-Planck-Gesellschaft. "Early modern humans interbred with Neanderthals: An early European had a close Neanderthal ancestor." ScienceDaily. ScienceDaily, 22 June 2015. 

原文網址：http://www.sciencedaily.com/releases/2015/06/150622122718.htm

為何恐龍行經赤道卻不定居下來？

原文網址：www.sciencedaily.com/releases/2015/06/150615152436.htm

Why did the dinosaur cross the equator, then not stay there?

Wild climate swings -- persisting tens of millions of years -- were too much for the dinos

為何恐龍行經赤道卻不定居下來？

持續了數千萬年之久的劇烈氣候動盪，對恐龍來說太難以承受

For more than 30 million years after dinosaurs first appeared, they remained inexplicably rare near the equator, where only a few small-bodied meat-eating dinosaurs eked out a living. The age-long absence of big plant-eaters at low latitudes is one of the great, unanswered questions about the rise of the dinosaurs.

在首批恐龍出現後的3000萬年間，赤道附近的恐龍種類難以解釋的稀少，僅有幾種體型小的肉食性恐龍在那裡勉強求生。大型草食性恐龍在如此長的時間中未出現於低緯度地區，為恐龍崛起的種種謎團中，最大的未解之謎之一。

And now the mystery has a solution, according to an international team of scientists who pieced together a remarkably detailed picture of the climate and ecology more than 200 million years ago at Ghost Ranch in northern New Mexico, a site rich with fossils from the Late Triassic Period.

新墨西哥州北部的幽靈農場(Ghost Ranch)為一座晚三疊紀的化石寶庫。現在國際科學家團隊藉由拼湊出當地超過2億年前的生態與氣候的詳盡樣貌，解答了這個謎題。

The new findings show that the tropical climate swung wildly with extremes of drought and intense heat. Wildfires swept the landscape during arid regimes and continually reshaped the vegetation available for plant-eating animals.

這項新發現顯示當時的熱帶氣候變動劇烈且受到極端的乾旱與高熱影響。在乾旱時期野火肆虐大地，迫使可供草食動物食用的植被不斷重新生長。

"Our data suggest it was not a fun place," says study co-author Randall Irmis, curator of paleontology at the Natural History Museum of Utah and assistant professor at the University of Utah. "It was a time of climate extremes that went back and forth unpredictably and large, warm-blooded dinosaurian herbivores weren't able to exist nearer to the equator -- there was not enough dependable plant food."

「我們的數據顯示當時那裡可不是個宜人的地方，」共同作者Randall Irmis說，其為猶他自然歷史博物館(the Natural History Museum of Utah)的古生物研究員與猶他大學(the University of Utah)的助理教授。「當時的極端氣候變化劇烈且捉摸不定。溫血的草食恐龍不可能生存在赤道附近，因為在那裡可靠的植物糧食來源並不足。」

The study, led by geochemist Jessica Whiteside, lecturer at the University of Southampton, is the first to provide a detailed look at the climate and ecology during the emergence of the dinosaurs. The results are important, also, for understanding human-caused climate change. Atmospheric carbon dioxide levels during the Late Triassic were four to six times current levels. "If we continue along our present course, similar conditions in a high-CO2 world may develop, and suppress low-latitude ecosystems," Irmis says.

本研究由南安普敦大學(he University of Southampton)的講師，地球化學家Jessica Whiteside所領導，為首篇詳細描述恐龍出現時的氣候與生態的研究。這些結果對於了解人類造成的氣候變遷也十分重要。晚三疊紀時大氣中的二氧化碳濃度是現今的四至六倍。「若我們還是一意孤行，環境可能會逐漸變成類似那時的高二氧化碳世界，而打擊低緯度的生態系。」Irmis說。

The other authors are Sofie Lindström, Ian Glasspool, Morgan Schaller, Maria Dunlavey, Sterling Nesbitt, Nathan Smith and Alan Turner. They report the findings today in the Proceedings of the National Academy of Sciences.

其它作者分別為Sofie Lindström、Ian Glasspool、Morgan Schaller、Maria Dunlavey、Sterling Nesbitt、Nathan Smith與Alan Turner。他們的研究成果發表在今日(2015.06.15)的《美國國家科學院院刊》(the Proceedings of the National Academy of Sciences)。

Reconstructing the deep past

重建遠古時光

The earliest known dinosaur fossils, found in Argentina, date from around 230 million years ago. Within 15 million years, multitudes of species with different diets and body sizes had evolved and were abundant beyond the tropical latitudes. In the tropics, the only dinosaurs present were small carnivores. This pattern persisted for 30 million years after the first dinosaurs appeared.

最早的恐龍化石發現於阿根廷，年代為2億3000萬年左右。之後的1500萬年間，恐龍演化出各式各樣的體型與飲食特性，並在熱帶地區以外的地方繁榮生長。而在熱帶地區唯一出現的恐龍為小型的肉食恐龍。在首批恐龍出現後的3000萬年間，牠們的分佈一直維持著這種模式。

In the new study, the authors focused on Chinle Formation rocks, which were deposited by rivers and streams between 205 and 215 million years ago at Ghost Ranch (better known to many outside of paleontology as the place where artist Georgia O'Keeffe lived and painted for much of her career). The multi-colored rocks of the Chinle Formation are a common sight on the Colorado Plateau at places such as the Painted Desert at Petrified Forest National Park in Arizona. During the Late Triassic, North America and other land masses of the world were bound together in the supercontinent Pangea. The Ghost Ranch site stood close to the equator at roughly the same latitude as present-day southern India.

在本篇新研究中，作者們將焦點放在幽靈農場2億500萬至2億1500萬年前，由河流沉積而成的欽迪組(Chinle Formation)岩石(對不熟悉古生物學的許多人來說，幽靈農場較知名之處為藝術家喬治亞·歐姬芙(Georgia O'Keeffe)職業生涯中，長期定居且完成許多畫作的地方)。色彩斑斕的欽迪組岩石為科羅拉多高原的常見景觀，亞利桑那州石化森林國家公園(Petrified Forest National Park)中的繪畫沙漠(the Painted Desert)即為一例。晚三疊紀時，北美與世界上的許多其他陸塊結合成盤古超大陸(the supercontinent Pangea)。當時的幽靈農場所在的緯度接近於赤道，約莫等同現今的南印度。

The researchers reconstructed the deep past by analyzing several kinds of data: fossils, charcoal left by ancient wildfires, and stable isotopes from organic matter and carbonate nodules that formed in ancient soils. "Each dataset complements the others, and they all point towards similar conditions," Whiteside says. "I think this is one of the major strengths of our study."

研究人員藉由分析數種資料來重建遠古時光，這些資料包括：化石、古代野火燒剩的木炭、有機物及古土壤中的碳酸鹽結核(carbonate nodule)的穩定同位素。「這些資料彼此之間能夠互補且它們傳達出的環境條件十分類似，」Whiteside說，「我認為這是我們這篇研究的有力之處之一。」

Fossilized bones, pollen grains and fern spores revealed the types of animals and plants living at different times, marked by layers of sediment. Dinosaurs remained rare among the fossils, accounting for less than 15 percent of vertebrate animal remains. They were outnumbered in diversity, abundance and body size by the reptiles known as Pseudosuchian archosaurs, the lineage that gave rise to crocodiles and alligators.

沉積岩中不同層裡面的化石骨骸、花粉顆粒與蕨類孢子代表了生活在不同時間的動植物種類。恐龍的遺骸在化石中相對來說較為稀少，僅占脊椎動物骨骸總數的15%以下。而後裔為鱷魚及短吻鱷的爬蟲類--主龍類(archosauria)的偽鱷亞目(pseudosuchia)不管在多樣性、數目與體型上都超出恐龍許多。

The sparse dinosaurs consisted mostly of small, carnivorous theropods. Big, long-necked dinosaurs, or sauropodomorphs -- already the dominant plant-eaters at higher latitudes -- did not exist at the study site or any other low-latitude site in Triassic Pangaea, as far as the fossil record shows.

這些為數不多的恐龍以小型的肉食性獸腳亞目(theropoda)為主。就現有的化石紀錄顯示，三疊紀時大型的長頸恐龍，或稱蜥腳形亞目(sauropodomorpha)，雖然已在盤古大陸較高緯度的地區成為主要的的草食動物，卻不存在於研究區域或者其他的低緯度地帶。

Abrupt changes in climate left a record in the shifting abundance of different types of pollen and fern spores between sediment layers. Fossilized organic matter from decaying plants provided another window on climate shifts. Changes in the ratio of stable isotopes of carbon in the organic matter bookmarked times when plant productivity declined during extended droughts.

突來的氣候變遷會造成沉積岩層中不同種類的花粉與孢子的數量改變而留下紀錄。植物腐爛後遺留的化石有機物也可以反映出氣候變遷。這些有機物中碳同位素比例的變化能夠標記出由於長期乾旱導致生產力下降的時期。

Drought and fire

乾旱與野火

Wildfire burn temperatures varied drastically, the researchers found, consistent with a fluctuating environment in which the amount of combustible plant matter rose and fell over time. The researchers estimated the intensity of wildfires using bits of charcoal recovered in the sediment layers. The amount of light reflected from the fossil charcoal under a light microscope relates directly to the burn temperature of the wood. The overall picture, the authors say, is that of a climate punctuated by extreme shifts in precipitation in which plant die-offs fueled hotter fires, which in turn killed more plants, damaged soils and increased erosion.

研究人員發現野火燃燒時的溫度的變化十分劇烈，這跟當時變動極大的環境中，可燃植物的數量會隨時間而有所增減相符。他們利用從沉積岩層中取出的微量木炭來估計野火的強度。在顯微鏡下木炭化石反射的光線量，會與木材燃燒時的溫度直接相關。作者說，當時的氣候整體上會穿插降雨極少的時期，在此時期火勢受乾枯的大量植物助長而變得更高溫，導致更多的植物死亡，並破壞水土保持而使侵蝕加劇。

Atmospheric carbon dioxide levels, calculated from stable isotope analyses of soil carbonate and preserved organic matter, rose from about 1,200 parts per million at the base of the section, to about 2,400 parts per million near the top. At these high CO2 concentrations, climate models predict more frequent and more extreme weather fluctuations consistent with the fossil and charcoal evidence.

分析土壤中的碳酸鹽及保存下來的有機物中的穩定同位素，他們估計研究區間的大氣二氧化碳濃度從開始時的1200 ppm，至結束時已攀升至2400 ppm。在這種二氧化碳濃度極高的環境下，氣候模型預測天氣變化會更為頻繁且愈加極端，與化石及木炭證據呈現出的情況相符。

Continuing shifts between extremes of dry and wet likely prevented the establishment of dinosaur-dominated communities found in the fossil record at higher-latitudes across South America, Europe and southern Africa, where aridity and temperatures were less extreme and humidity was consistently higher. Resource-limited conditions could not support a diverse community of fast-growing, warm-blooded, large dinosaurs, which require a productive and stable environment to thrive.

不斷發生的極端乾濕變化，可能造成當地無法建立如同南美、歐洲與非洲南部的化石紀錄中，以恐龍為主的動物群集。在那些地區的乾旱與氣溫不那麼極端，濕度也高的穩定。資源有限的環境難以支持由許多種類的成長快速、溫血的大型恐龍所組成的群集，因為牠們的生存依賴豐饒且穩定的環境。

"The conditions would have been something similar to the arid western United States today, although there would have been trees and smaller plants near streams and rivers and forests during humid times," says Whiteside. "The fluctuating and harsh climate with widespread wild fires meant that only small two-legged carnivorous dinosaurs, such as Coelophysis, could survive."

「當時的環境跟現在美國西部的乾燥地區有些類似。雖然在河流沿岸可能會有樹木及小型植物生長，濕潤時期也可能會有森林發育，」Whiteside說。「然而動盪且嚴峻的氣候，以及大片的野火，造成僅有某些小型的雙足肉食恐龍，例如腔骨龍(Coelophysis)才能夠生活於此。」

引用自University of Utah. "Why did the dinosaur cross the equator, then not stay there? Wild climate swings -- persisting tens of millions of years -- were too much for the dinos." ScienceDaily. ScienceDaily, 15 June 2015.