緩緩移動的斷層或許預示了地震即將到來

原文網址：www.sciencedaily.com/releases/2016/04/160405114218.htm

Slow fault movements may indicate impending earthquakes

緩緩移動的斷層或許預示了地震即將到來

Scientists from Nanyang Technological University (NTU Singapore) at its Earth Observatory of Singapore (EOS) have discovered a way to forecast earthquakes based on slow fault movements caused by moving sub layers of Earth.

南洋理工大學駐新加坡地球觀測站的科學家發現，藉由觀察地球內部地層錯動而引發的緩慢斷層活動，可以用來預告地震即將發生。

So far, scientists believe that larger earthquakes are unlikely to occur following tremors or earthquakes below a Richter scale of 2 that are caused by small vibrations or slow fault movements such as those observed in the area of Parkfield along the San Andreas Fault in California, USA.

目前為止，科學家依據觀測像美國加州聖安地列斯斷層上帕克菲爾德(Parkfield)地區的結果，認為在小型振動或斷層緩慢移動而引發了芮氏規模小於2的微震或地震之後，不可能會有大型地震接著發生。

However, the NTU team found that not only do these vibrations potentially point to an impending earthquake, they also discovered a discernible pattern to them.

然而，南洋理工大學不僅發現這種振動可能指出了地震即將到來，甚至還發現它們之間有可以依循的模式。

"This discovery defied our understanding of how faults accumulate and release stress over time. These vibration patterns are caused by alternating slow and fast ruptures occurring on the same patch of a fault," said Asst Prof Sylvain Barbot, from NTU's Asian School of the Environment and an earth scientist at EOS.

「這項發現挑戰了我們對於斷層隨著時間會如何累積與釋放應力的知識。在同一段斷層上因為破裂反覆地快慢交替發生，而造成了這種振動模式。」南洋理工大學亞洲環境學院的助理教授 Sylvain Barbot說，他也是新加坡地球觀測站的地球科學家。

"If only slow movements are detected, it does not mean that a large earthquake cannot happen there. On the contrary, the same area of the fault can rupture in a catastrophic earthquake," he warned.

「若在某個區段觀測到只有緩慢的運動發生，也不代表說這個區域之後就不會發生大地震。相反地，斷層上的同一區域有可能在將來破裂而發生毀滅性大地震。」他提出了這樣的警告。

The study, which has major significance on the prediction of earthquakes, was led by Asst Prof Barbot's PhD student, Miss Deepa Mele Veedu. It was published in Nature.

此篇對於地震預測有重大貢獻的研究刊登於《自然》期刊之上，主持人為 Barbot助理教授的博士生， Deepa Mele Veedu女士。

Seismic hazards in the Southeast Asia region will probably come from an impending large earthquake in the Mentawai seismic gap in Sumatra, Indonesia -- a current area of active monitoring and investigation.

東南亞地區的下一次地震災害可能會由印尼蘇門答臘明打威(Mentawai )地震空白帶(seismic gap)的大型地震造成。此地區現有大量的監測和調查活動進行中。

EOS scientists have earlier pointed out a large earthquake may occur any time in this area southwest of Padang -- the only place along a large fault where a big earthquake has not occurred in the past two centuries. The team's latest findings could potentially be applied in the seismic monitoring of the area to help better forecast large earthquakes in the region.

新加坡地球觀測站的科學家先前早已指出巴東(Padang )西南方隨時都可能發生大型地震。因為此地區是一條大型斷層帶上過去2個世紀以來唯一還未發生大地震的區域。此團隊最新的研究或許可以運用在巴東地區的地震監測上，而提高預測此地區地震的準確性。

EOS conducts fundamental research on earthquakes, volcanic eruptions, tsunamis and climate change in and around Southeast Asia, towards safer and more sustainable societies.

新加坡地球觀測站主要著重於東南亞及鄰近地區的地震、火山爆發、海嘯和氣候變遷的基礎研究。它們的宗旨是要創造更安全且更能永續發展的社會。

引用自：Nanyang Technological University. "Slow fault movements may indicate impending earthquakes." ScienceDaily. ScienceDaily, 5 April 2016. 

如何在大滅絕事件中存活下來？匆匆活著，早早死去

原文網址：www.sciencedaily.com/releases/2016/04/160405093103.htm

How to survive a mass extinction: Live fast, die young

如何在大滅絕事件中存活下來？匆匆活著，早早死去

Life history of ancient mammal relatives provides insight on survival tactics

古代哺乳類近親的生活史讓我們得以了解牠們的生存策略

Two hundred and fifty-two million years ago, a series of Siberian volcanoes erupted and sent the Earth into the greatest mass extinction of all time. As a result of this mass extinction, known as the Permo-Triassic Mass Extinction, billions of tons of carbon were propelled into the atmosphere, radically altering the Earth's climate. Yet, some animals thrived in the aftermath and scientists now know why.

2億5200萬年前，西伯利亞一連串的火山噴發事件引發了地球史上規模最劇的大滅絕事件。又稱作二疊紀-三疊紀滅絕事件(Permo-Triassic Mass Extinction)的那次大滅絕將數十億噸的碳噴發至大氣當中，因而劇烈改變了地球氣候。即使如此，仍有一些動物在這次浩劫過後倖存下來，而科學家現今知道牠們是如何辦到的。

In a new study published in Scientific Reports, a team of international paleontologists, including postdoctoral scholar Adam Huttenlocker of the Natural History Museum of Utah at the University of Utah, demonstrate that ancient mammal relatives known as therapsids were suited to the drastic climate change by having shorter life expectancies and would have had a better chance of success by breeding at younger ages than their predecessors.

在這篇發表於《科學報導》(Scientific Reports)期刊中的新研究，由國際古生物學家組成的團隊描述了一種哺乳類的古代表親，稱作「獸孔目」(therapsid)的動物藉由活得比預期壽命(life expectancy)要短來適應如此激烈的氣候變遷。跟牠們的祖先相比，牠們在較年輕時就開始繁殖後代來讓整體有較高的存活率。作者群之一包括了猶他州立大學猶他州立博物館的博士後研究學者 Adam Huttenlocker。

The research team studied growth patterns in therapsids from the South African Karoo Basin, a paleontologically significant area which preserves a wide range of fossils from the Permian to the Early Jurassic, or 300-180 million years ago.

研究團隊探討了來自南非卡魯盆地(Karoo Basin)的獸孔目化石的生長模式。這個盆地保存了年代為3億年至1億8000萬年前，也就是二疊紀至侏儸紀早期各式各樣的化石，因此在古生物學上具有重要地位。

By examining their bone microstructure before and after the extinction boundary, Huttenlocker and his colleagues were able to study how growth patterns in therapsids were affected by the extinction. By studying body size distributions in particularly abundant species from the Permian and Triassic, the team was able to interpret shifts in size class structure and in rates of survivorship.

Huttenlocker 和他的同僚藉由檢視大滅絕前後獸孔目化石骨骼中的微構造，來探討大滅絕如何影響牠們的生長模式。研究團隊研究了從二疊紀至三疊紀數量皆相當豐富的物種的個體體型分布情況，進而了解牠們體型分佈的結構和存活率如何變化，

In this study, special attention was paid to the genus Lystrosaurus because of its success in surviving the Permo-Triassic extinction; it dominated ecosystems across the globe for millions of years during the post-extinction recovery period, and makes up some 70-90% of the vertebrate fossils found in Early Triassic rocks in the Karoo.

此研究特別將注意力聚焦在水獸龍屬(Lystrosaurus)身上，這是因為牠們很成功地在二疊紀-三疊紀滅絕事件中倖存下來，並在大滅絕過後的回復期中統治了全球生態系數百萬年的時間。卡魯盆地早三疊統岩石裡的脊椎動物化石中，牠們就佔了總數的70至90%。

"Therapsid fossils like Lystrosaurus are important because they teach us about the resilience of our own extinct relatives in the face of extinction, and provide clues to which traits confered success on lineages during this tubulent time. Lystrosaurus was particularly prolific, making it possible to build a large dataset and to sacrifice some specimens for histology to study the growth patterns recorded in its bones," said Huttenlocker, one of the paper's authors.

「水獸龍之類的獸足類化石之所以如此重要，在於牠們告訴了我們在遭遇大滅絕事件時，我們這些已消失的近親有多麼頑強；還有在這段混亂不堪的時期，具有何種特徵的後裔子孫才能夠成功存活下來。水獸龍數目眾多的特性讓我們得以建立起內容豐富的資料庫，並且使我們可以犧牲某些樣品來進行組織學研究，以得到記錄在骨骼當中的生長模式。」作者之一 Huttenlocker說。

"Before the Permo-Triassic extinction, the famous therapsid Lystrosaurus had a life span of about 13 or 14 years based on the record of growth preserved in their bones," said Field Museum paleontologist Ken Angielczyk, another one of the paper's authors. "Yet, nearly all of the Lystrosaurus specimens we find from after the extinction are only 2¬-3 years old. This implies that they must have been breeding when they were still [relatively young] themselves."

「根據保存在骨骼當中的成長紀錄，這些著名的獸孔目水獸龍在二疊紀-三疊紀滅絕事件前的壽命大約為13至14歲。」此論文的另外一位作者，菲爾德自然史博物館的古生物學家 Ken Angielczyk說。「但是，在大滅絕之後我們發現的水獸龍樣品幾乎都僅僅只有2到3歲。這意味著牠們勢必在年幼時(相對於牠們自身所屬的物種)就已經繁衍了下一代。」

This adjustment in life history also meant a physical change for Lystrosaurus. Before the mass extinction, this creature would have been a couple meters long and weighed hundreds of pounds--about the size of a pygmy hippo. Post-extinction, its size dropped to that of a large dog, in large part due to its altered lifespan. Yet, these adaptations seemed to pay off for Lystrosaurus. Ecological simulations show that by breeding younger, Lystrosaurus could have increased its chance of survival by 40% in the unpredictable environments that existed in the aftermath of the extinction.

水獸龍在生命史長度上做出的調適意味著牠們的生理結構同時也產生了變化。在大滅絕之前，這些生物的身長大約有2公尺並且重達數百磅，跟侏儒河馬的體型相偌。但在大滅絕之後，牠們的體型迅速縮小成跟大型犬差不多大，這多半跟牠們的壽命改變有關。然而，對水獸龍而言這種適應似乎相當值得。生態模型顯示在大滅絕過後，水獸龍在這種變化莫測的環境下，可以藉由在年輕時就繁殖下一代，而提高40%的存活率。

This change in breeding behavior is not isolated to ancient animals either. In the past century, the Atlantic cod has undergone a similar effect due to human interference. Industrial fishing has removed most large individuals from the population, shifting the average size of cod significantly downward. Likewise, the remaining individuals are forced to breed as early in their lives as possible. Similar shifts have also been demonstrated in African monitor lizards exploited by humans.

這種繁殖策略的改變並不僅只局限於古代動物。在上個世紀，大西洋鱈也因為人類的干擾而經歷了這種變化。捕魚工業化幾乎撈除了族群中所有的大型個體，造成鱈魚的平均體型迅速縮小。同樣地，剩餘的個體被迫要盡量在還相當年輕時就繁殖後代。相同的變化也在被人類捕捉過後的非洲巨蜥身上描述到。

"Although it's hard to see the effects in our daily lives, there is substantial evidence that we are in the middle of a sixth mass extinction right now. It has been predicted that half of mammal species could become extinct by the end of the next century if present patterns continue; that's more than 1,000 times greater than previous estimates of natural extinctions, a trend not seen since the End-Permian or End-Cretaceous extinctions," said Huttenlocker.

「雖然在我們的日常生活中很難看到這類效應，但這的確是我們現在正處於第六次大滅絕的堅實證據。科學家預測若繼續維持現今的滅絕模式，在下個世紀末將會有一半的哺乳類動物就此消失。在這種模式下物種滅亡的速度是先前預估自然滅絕亡速率的1000倍以上，這是自二疊紀末或白堊紀末的大滅絕之後前所未見的。」 Huttenlocker說。

"With the world currently facing its sixth mass extinction, paleontological research helps us understand the world around us today," said Angielczyk. "By studying how animals like Lystrosaurus adapted in the face of disaster, we can better predict how looming environmental changes may affect modern species."

「在世界正經歷第六次大滅絕的此時，古生物研究可以讓我們更加了解周遭世界發生的一切。」 Angielczyk說。「藉著研究水獸龍這類的動物如何在面臨災禍時適應環境，我們可以更準確地預測悄然逼近的環境變遷會如何影響現存的生物。」

引用自：University of Utah. "How to survive a mass extinction: Live fast, die young: Life history of ancient mammal relatives provides insight on survival tactics." ScienceDaily. ScienceDaily, 5 April 2016. 

在地球磁場的維持上月球也許具有關鍵地位

原始網址：www.sciencedaily.com/releases/2016/04/160401075118.htm

The Moon may play a major role in maintaining Earth's magnetic field

在地球磁場的維持上月球也許具有關鍵地位

The Earth's magnetic field permanently protects us from the charged particles and radiation that originate in the Sun. This shield is produced by the geodynamo, the rapid motion of huge quantities of liquid iron alloy in the Earth's outer core. To maintain this magnetic field until the present day, the classical model required the Earth's core to have cooled by around 3,000 °C over the past 4.3 billion years. Now, a team of researchers from CNRS and Université Blaise Pascal[1] suggests that, on the contrary, its temperature has fallen by only 300 °C. The action of the Moon, overlooked until now, is thought to have compensated for this difference and kept the geodynamo active. Their work is published on 30 march 2016 in the journal Earth and Planetary Science Letters.

地球磁場長久以來保護我們免受來自太陽的帶電粒子和輻射所造成的傷害。這道屏障是由「地球發電機」(geodynamo)產生，此效應是因地球外核中的巨量液態鐵合金迅速流動而造成的。傳統模型認為要讓地球磁場維持至今日，地核必須在43億年的歲月中降溫將近3000°C。相反地，法國國家科學研究中心和克萊蒙費朗第二大學的研究人員近日提出的學說認為，地核溫度僅需降溫300°C就能維持地球磁場。他們認為彌補這個溫度差以及維繫地球發電機運作的關鍵因素是直到現在才被注意到的月球運動。這項研究刊登於2016年3月30日的《地球與行星科學通訊》期刊。

The classical model of the formation of Earth's magnetic field raised a major paradox. For the geodynamo to work, the Earth would have had to be totally molten four billion years ago, and its core would have had to slowly cool from around 6800 °C at that time to 3800 °C today. However, recent modeling of the early evolution of the internal temperature of the planet, together with geochemical studies of the composition of the oldest carbonatites and basalts, do not support such cooling. With such high temperatures being ruled out, the researchers propose another source of energy in their study.

傳統模型在解釋地球磁場如何形成時具有一個重大的矛盾。若要讓地球發電機運轉，地球在四十億年前必須要處於完全熔融的狀態，在這之後地核得從將近6800°C的高溫緩緩降溫至現今的 3800 °C。然而，最近模擬早期地球內部溫度如何演變的結果，以及對最古老的碳酸岩(carbonatite)和玄武岩成分進行的地球化學研究，皆不支持這樣的冷卻過程。由於上述結果排除掉如此高溫為可能的能量來源，所以這些研究人員在他們的研究之中提出了另外一種來源。

The Earth has a slightly flattened shape and rotates about an inclined axis that wobbles around the poles. Its mantle deforms elastically due to tidal effects caused by the Moon. The researchers show that this effect could continuously stimulate the motion of the liquid iron alloy making up the outer core, and in return generate Earth's magnetic field. The Earth continuously receives 3,700 billion watts of power through the transfer of the gravitational and rotational energy of the Earth-Moon-Sun system, and over 1,000 billion watts is thought to be available to bring about this type of motion in the outer core. This energy is enough to generate the Earth's magnetic field, which together with the Moon, resolves the major paradox in the classical theory. The effect of gravitational forces on a planet's magnetic field has already been well documented for two of Jupiter's moons, Io and Europa, and for a number of exoplanets.

地球的外型略呈扁平且以一根傾斜的轉軸為軸心自轉，而這根自轉軸本身也會繞著一個圓圈晃動；另外，地函內部也會發生塑性變形。以上的作用或多或少都跟月球造成的潮汐力有關。研究人員顯示這個作用力同樣也能促使組成外核的液態鐵合金不斷運動，進而產生地球磁場。在地球-月球-太陽系統中，重力和彼此繞行時產生的能量會持續轉換至地球身上，功率高達3兆7000億瓦。研究人員相信這些能量當中有超過1兆瓦被用來驅動外核中的這類運動，而如此龐大的能量足以產生地球磁場。因此將月球這項因子考量在內，便能夠解決傳統理論中的重大矛盾。在木星的兩顆衛星，木衛一「埃歐」及木衛二「歐羅巴」，還有一些地外行星上已經詳細記錄到這種重力對星球磁場的影響。

Since neither the Earth's rotation around its axis, nor the direction of its axis, nor the Moon's orbit are perfectly regular, their combined effect on motion in the core is unstable and can cause fluctuations in the geodynamo. This process could account for certain heat pulses in the outer core and at its boundary with the Earth's mantle.

既然地球自轉、地軸指向以及月球軌道這三者都並非是照著完美的規律運作，它們聯合起來對地核流動造成的效應就不會是穩定的，因此會造成地球發電機內部發生擾動。這可以用來解釋外核內部以及核幔邊界處發生的部分熱能高漲現象。

Over the course of time, this may have led to peaks in deep mantle melting and possibly to major volcanic events at the Earth's surface. This new model shows that the Moon's effect on the Earth goes well beyond merely causing tides.

長久下來，這種現象可能使深部地函的頂部熔融，並在地球表面造成重大的火山噴發事件。這個新模型顯示月球對地球造成的影響之大可不僅只有潮汐而已。

[1] At the Laboratoire Magmas et Volcans (CNRS/IRD/Université Blaise Pascal), part of the Observatoire de Physique du Globe de Clermont-Ferrand, the Institut de Recherche sur les Phénomènes Hors-équilibre (CNRS/Aix-Marseille Université/Ecole Centrale Marseille) and the Institut de Recherche en Astrophysique et Planétologie (CNRS/Université Toulouse III -- Paul Sabatier).

來源自：CNRS. "The Moon may play a major role in maintaining Earth's magnetic field." ScienceDaily. ScienceDaily, 1 April 2016.  

印尼的「哈比人」也許比之前認為的還要早滅絕

原文網址：www.sciencedaily.com/releases/2016/03/160330135304.htm

Indonesian 'Hobbits' may have died out sooner than thought

印尼的「哈比人」也許比之前認為的還要早滅絕

An ancient species of pint-sized humans discovered in the tropics of Indonesia may have met their demise earlier than once believed, according to an international team of scientists who reinvestigated the original finding.

根據一個國際科學家團隊重新調查的結果，於熱帶印尼發現的一種矮小的古代人種，他們比當初發現時認為的還要早迎接滅亡。

Published in the journal Nature this week, the group challenges reports that these inhabitants of remote Flores island co-existed with modern humans for tens of thousands of years.

之前發表的論文認為這些住在遠離塵囂的佛羅勒斯島上的居民，曾經跟現代人共同生活了數萬年之久。但本周刊登於《自然》(Nature)期刊上的論文則對此說法提出了質疑。

They found that the youngest age for Homo floresiensis, dubbed the 'Hobbit', is around 50,000 years ago not between 13,000 and 11,000 years as initially claimed.

他們發現這些暱稱為「哈比人」的佛羅勒斯人(Homo floresiensis)年代最近的骨骸為距今50,000年前，而非原先聲稱的距今11,000年前。

Led by Indonesian scientists and involving researchers from Griffith University's Research Centre of Human Evolution (RCHE) the team found problems with prior dating efforts at the cave site, Liang Bua.

這個團隊由印尼的科學家領導，並且有格里菲斯大學人類演化中心(RCHE)的研究人員參與其中。他們發現之前對這些骨骸出土的洞穴場址-梁布亞(Liang Bua)進行的定年方法有些問題。

"In fact, Homo floresiensis seems to have disappeared soon after our species reached Flores, suggesting it was us who drove them to extinction," says Associate Professor Maxime Aubert, a geochronologist and archaeologist at RCHE, who with RCHE's Director Professor Rainer measured the amount of uranium and thorium inside Homo floresiensis fossils to test their age.

「事實上，佛羅勒斯人似乎在我們所屬的物種到達佛羅勒斯島不久後就消失了。這意味著他們的滅亡是由我們促成的。」 RCHE的地質定年學家及考古學家 Maxime Aubert副教授說。他跟RCHE的計畫主持人， Rainer教授測量了佛羅勒斯人化石中的鈾和釷含量，以測得他們的生存年代。

"The science is unequivocal,'' Aubert said.

「這些科學證據可說無庸置疑。」Aubert說。

"The youngest Hobbit skeletal remains occur at 60,000 years ago but evidence for their simple stone tools continues until 50,000 years ago. After this there are no more traces of these humans."

「年代最近的哈比人化石大約是距今60,000年前，而他們遺留下來的粗糙石器則證明了他們直到55,000年前仍生活於此。然而在這之後就再也沒有這些人類生存於此的蛛絲馬跡了。」

While excavating at the limestone cave of Liang Bua in 2003, archaeologists found bones from diminutive humans unlike any people alive today. The researchers concluded the tiny cave dwellers evolved from an older branch of the human family that had been marooned on Flores for at least a million years. It was thought that this previously unknown population lived on Flores until about 12,000 years ago.

考古學家於2003年挖掘了位於梁布亞的石灰岩洞穴，並發現這些跟現今生存的人們截然不同的矮小人類骨骸。研究人員得出的結論認為這些矮小的穴居人是從人屬中古老的一支演化而來，他們漂流並孤立在佛羅勒斯島上至少已有100萬年的歷史。過去認為這群前所未見的人種至少在距今12,000年前都還生活在佛羅勒斯島上。

But the site is large and complex and the original excavators dug only a tiny portion of it. Years of further excavation has led to a much clearer understanding of the order of archaeological layers. It is now evident that when the original team collected samples for dating the main layer containing Hobbit bones they mistakenly took them from an overlying layer that is similar in composition, but far younger.

然而，最初開挖工作挖掘的只不過是這個巨大且複雜的遺址的一部分而已。經過數年的後續開挖工作後，研究人員更加瞭解了這些考古地層的年代先後順序。現在他們確知原先的團隊在定年含有哈比人化石的主要岩層時，他們誤從上覆的岩層採集樣品，雖然成分相似，然而年代卻年輕了許多。

"This problem has now been resolved and the newly published dates provide a more reliable estimate of the antiquity of this species,'' Aubert said.

「我們現在已經解決了這項問題。在新發表的論文中，我們提供了對這個物種的年代更可信的預估結果。」

But the mystery of what happened to these creatures remains.

然而，這個物種遭遇的一切仍然是個懸而未解的謎團。

RCHE archaeologist Dr Adam Brumm, who also participated in the study, said Hobbits are likely to have inhabited other Flores caves which may yield more recent signs of their existence. He believes Homo floresiensis probably suffered the same fate that befell Europe's Neanderthals -- our species simply out-competed and replaced them within a few thousand years.

同樣參與了此研究的RCHE考古學家，Adam Brumm教授說哈比人很可能也曾在佛羅勒斯島上的其他洞穴居住過，而我們或許能從中取得他們生活過的證據，且比先前的年代還要更近。他相信佛羅勒斯人遭受的厄運跟降臨在歐洲尼安德塔人身上的相同-我們這個物種在幾千內便淘汰並徹底取代了他們。

"They might have retreated to more remote parts of Flores, but it's a small place and they couldn't have avoided our species for long. I think their days were numbered the moment we set foot on the island."

「他們相當有可能撤離到佛羅勒斯島上更加隱密之處，但那蕞爾之地並不足以讓他們逃離我們這個物種的威脅太久。我想當我們登上這座島嶼的那一刻開始，他們的喪鐘就已經響起了。」

引用自：Griffith University. "Indonesian 'Hobbits' may have died out sooner than thought." ScienceDaily. ScienceDaily, 30 March 2016. 

許多瀕臨滅絕的物種有可能未留下化石紀錄就此消失

原始網址：www.sciencedaily.com/releases/2016/03/160321200445.htm

Many species now going extinct may vanish without a fossil trace

Human-made 'sixth extinction' may seem small compared to five prehistoric die-offs

許多瀕臨滅絕的物種有可能未留下化石紀錄就此消失

人類導致的第六次大滅絕規模與前五次史前大滅絕相比看似小了許多

Scientists struggle to compare the magnitude of Earth's ongoing sixth mass-extinction event with the five great die-offs of prehistory. A new study by three paleontologists shows that the species now perishing may vanish without a permanent trace -- and earlier extinctions may be underestimated as well.

科學家力圖比對地球上正在發生的第六次大滅絕和前五次史前大滅絕事件之間的差異。一項由三位古生物學家進行的新研究顯示，現今的瀕危物種可能不留下一絲能保存良久的記錄便就此消失，而我們或許也低估了過往大滅絕事件的規模。

"Comparing the current biodiversity crisis, often called the 'sixth extinction,' with those of the geological past requires equivalent data," says Roy Plotnick, professor of earth and environmental sciences at the University of Illinois at Chicago.

「我們需要對等的資料才能將現今發生的生物多樣性危機，又稱『第六次大滅絕』跟地質史上的其他次滅絕事件互相比較。」芝加哥伊利諾大學的地球與環境科學教授 Roy Plotnick說。

He and two colleagues compared the "Red List" of endangered species with several ecological databases of living species and three paleontological databases of catalogued fossils. They ran a statistical analysis to indicate which threatened species were most likely to disappear with no mark of their existence.

他和另外兩外同僚比對了編列瀕危物種的「紅皮書」(Red List)、數個紀錄現存動物的生態資料庫，以及三個記載已編目化石的古生物資料庫。接著他們進行統計分析以找出哪些受威脅的物種最有可能不留下牠們曾經存在的痕跡而永遠消失。

The researchers were shocked to find that more than 85 percent of the mammal species at high risk of extinction lack a fossil record. Those at highest risk have about half the probability of being incorporated into the fossil record compared to those at lower risk.

研究人員相當驚訝地發現高度瀕危的哺乳類物種中有85%以上會缺乏化石紀錄。面臨最高瀕危風險的物種成為化石紀錄一部分的機率，比那些處在較低風險的物種形成化石的機率低了一半。

Animals least likely to be found as fossils are "the small, cute and fuzzy ones, like rodents and bats," Plotnick said. "Body size is an obvious factor -- bigger things tend to leave a fossil record, as do things with larger geographical ranges."

動物中最難發現的化石便是那些「小巧可愛、毛茸茸的動物，像是齧齒類和蝙蝠」。 Plotnick說。「體型是相當明顯的要素，大型物種比較容易留下化石紀錄，而那些地理分布比較廣的也是。」

Viewed from the perspective of the fossil record alone, the magnitude of the current mammal die-off thus appears markedly reduced. The picture may be even more distorted for other land-dwelling vertebrates: only 3 percent of today's threatened bird species and 1.6 percent of threatened reptile species have a known fossil record.

若僅由化石紀錄的觀點來看，當今哺乳類的滅絕規模會顯得輕微了許多。對於其他陸生脊椎動物而言，從同樣的觀點出發可能會更加曲解牠們面臨的滅絕困境。今日備受威脅的鳥類中只有百分之3留下了為人所知的化石紀錄；而爬蟲類更是只有百分之1.6。

Comparing the scale of the current extinction episode, which is based primarily on terrestrial vertebrates, to earlier extinctions that are mostly calculated from the fossil record of hard-shelled marine invertebrates, is particularly problematic, Plotnick said, although ancient extinctions may also be underestimated by contemporary paleontologists.

Plotnick說現行的滅絕事件主要對象是陸生脊椎動物，然而過去滅絕事件的規模大多是利用具有硬殼的海生無脊椎動物化石紀錄來估算，因此要比較兩者的規模就會特別有問題。而現代的古生物學家也可能低估了古代滅絕事件的規模。

Nevertheless, fossils will provide the only reliable record of life on Earth for posterity.

然而，化石終究是地球生命留給後裔的紀錄中唯一可靠的。

"There are species going extinct today that have never been described," Plotnick said. "Others are going extinct that are known only because someone wrote it down." All such species would thus be unknown in the far future, he said, if the written historical record is lost -- as it might well be.

「今日許多邁向滅亡的物種是人們從來沒有記述到的。」 Plotnick說。「而其他消失的物種能夠為人所知僅僅是因為有人將牠書寫下來。」如果這些歷史文字紀錄消失，那麼所有這類物種在遙遠的未來都將被淡忘，而這確實很有可能發生，他說。

The fossil record, Plotnick points out, is much more durable than any human record.

Plotnick指出化石紀錄遠比人類所有的紀錄方式禁得起時間考驗。

"As humanity has evolved, our methods of recording information have become ever more ephemeral," he said. "Clay tablets last longer than books. And who today can read an 8-inch floppy?" he shrugged. "If we put everything on electronic media, will those records exist in a million years? The fossils will."

「隨著人類的進步，我們保存資訊的方式卻顯得越來越稍縱即逝。」他說。「泥片(clay tablet，巴比倫人將文字刻於其上)可以比書本流傳的更久。而今日又有誰能讀取8吋磁碟片？」他聳聳肩。「如果我們將所有事物都保存在電子裝置中，這些檔案可以存在百萬年之久嗎？無庸置疑的是化石絕對可以。」

Other authors on the study, published earlier this month in Ecology Letters, are Felisa A. Smith of the University of New Mexico and S. Kathleen Lyons of the National Museum of Natural History in Washington, D.C.

此篇本月稍早刊登於《生態學通訊》的論文的其他作者還包括了新墨西哥州大學的 Felisa A. Smith，以及華盛頓國立自然歷史博物館的 S. Kathleen Lyons。

引述自：University of Illinois at Chicago. "Many species now going extinct may vanish without a fossil trace: Human-made 'sixth extinction' may seem small compared to five prehistoric die-offs." ScienceDaily. ScienceDaily, 21 March 2016.