過往的海洋比我們認為得還要冷

過往的海洋比我們認為得還要冷

一組研究團隊發現目前為止用來估計過往海洋溫度的方法有所缺陷。他們的發現可能意味現在的氣候變遷是過去1億年以來前所未見的。

根據科學界常用的方法，在1億年以前海洋深處和極區海洋的表面溫度比現今的數值還要高了將近15度。但此方法如今受到考驗：這段時間以來海洋溫度可能實際上都保持著相對穩定的狀態，而令人更加憂心現今的氣候變遷程度。來自法國國家科學研究中心(CNRS)、索邦大學、史特拉斯堡大學的法國科學家，以及瑞士洛桑聯邦理工學院(EPFL)和洛桑大學的瑞士科學家近日刊登於《自然通訊》(Nature Communications)的研究得出了上述結論。

EPFL生物地球化學實驗室的主持人，同時也是洛桑大學的教授Anders Meibom表示：「如果我們是正確的，這項研究將會考驗數十年來的古氣候研究成果。」他明確指出：「海洋覆蓋了地球表面70%的面積，對於地球氣候來說具有非常重大的影響。如果我們想要完全瞭解海洋的運作方式，並且更加準確地預測現今氣候變遷的後果，就要先知道在地質時間中海洋溫度的變化程度。」

為什麼現行方法會有如此重大的缺陷？研究作者相信某些作用的影響一直都被忽略了。50多年以來科學家做出的預測都是基於研究有孔蟲的成果。有孔蟲是一種十分微小的海洋生物，從海床取出的沉積物岩芯中可以發現牠們的化石。依據存活當時所處的水溫，有孔蟲形成的鈣質外殼(稱作test)的氧-18含量會跟著變化。因此，利用從沉積物中找到的有孔蟲殼體，便可依據其氧-18含量來計算過去海洋溫度的變化歷程。根據之前做出的測量結果，海洋溫度在過去1億年來下降了大約15度。

但這些估算都是建立於一項原則：有孔蟲殼體化石保存在沉積物內部的期間，其氧-18含量是保持固定的。目前為止確實還沒有任何證據指出並非如此，不管是用肉眼或是顯微鏡都未看到有孔蟲化石產生變化。這篇最新研究的作者為了驗證自身的假設，他們在僅有氧-18的人工海洋中，讓這些小生物處在高溫環境之下。接著他們利用可以分析極小區域化學性質的儀器NanoSIMS(奈米級二次離子質譜儀)來觀察氧-18進入鈣質殼體的過程。結果證明有孔蟲殼體的氧-18含量實際上可以不留痕跡地發生變化，研究人員因此對其作為溫度計的可信度產生疑慮。「看起來保存十分完善的化石實際上並非如此。代表至今為主科學家對古海洋溫度做出的預測都是錯的。」研究主要作者Sylvain Bernard表示，他是CNRS位在巴黎的礦物學、材料物理學和宇宙化學研究所的研究人員。

對此法國和瑞士研究團隊來說，過往的測量結果並非反映出海洋溫度在過去1億年以來有逐漸下降的趨勢，僅代表有孔蟲殼體化石含有的氧-18本身的變化過程，而此變化似乎是由一種稱為再平衡(re-equilibration)的作用導致：沉積作用的過程中溫度會上升20至30℃，造成有孔蟲殼體跟周圍的水重新發生化學平衡。經過數千萬年之後，此作用會對古海溫的估算產生重大影響，特別是那些根據生存於冷水的有孔蟲所進行的研究。研究人員透過電腦模擬提出海洋深處和極區海洋表層的溫度之前都被估算得太高。

對Meibom來說，下一步十分明確：「為了重新審視古海洋溫度，我們需要仔細定量忽略已久的再平衡作用產生的影響。要達成這項目標，我們必須同時研究其他種類的海洋生物，才能徹底瞭解在地質時間尺度下，沉積物內部究竟發生了何種作用。」此文章的作者已經開始如火如荼地進行研究。

The oceans were colder than we thought

A team of researchers has discovered a flaw in the way past ocean temperatures have been estimated up to now. Their findings could mean that the current period of climate change is unparalleled over the last 100 million years.

According to the methodology widely used by the scientific community, the temperature of the ocean depths and that of the surface of the polar ocean 100 million years ago were around 15 degrees higher than current readings. This approach, however, is now being challenged: ocean temperatures may in fact have remained relatively stable throughout this period, which raises serious concerns about current levels of climate change. These are the conclusions of a study conducted by a team of French researchers from the French National Center for Scientific Research (CNRS), Sorbonne University and the University of Strasbourg, and Swiss researchers from the Swiss Federal Institute of Technology in Lausanne (EPFL) and the University of Lausanne. The study has just been published in Nature Communications.

“If we are right, our study challenges decades of paleoclimate research,” says Anders Meibom, the head of EPFL’s Laboratory for Biological Geochemistry and a professor at the University of Lausanne. Meibom is categorical: “Oceans cover 70% of our planet. They play a key role in Earth’s climate. Knowing the extent to which their temperatures have varied over geological time is crucial if we are to gain a fuller understanding of how they behave and to predict the consequences of current climate change more accurately.”

How could the existing methodology be so flawed? The study’s authors believe that the influence of certain processes was overlooked. For over 50 years, the scientific community based its estimates on what they learned from foraminifera, which are the fossils of tiny marine organisms found in sediment cores taken from the ocean floor. The foraminifera form calcareous shells called tests in which the content of oxygen-18 depends on the temperature of the water in which they live. Changes in the ocean’s temperature over time were therefore calculated on the basis of the oxygen-18 content of the fossil foraminifera tests found in the sediment. According to these measurements, the ocean’s temperature has fallen by 15 degrees over the past 100 million years.

Yet all these estimates are based on the principle that the oxygen-18 content of the foraminifera tests remained constant while the fossils were lodged in the sediment. Indeed, until now, nothing indicated otherwise: no change is visible to the naked eye or under the microscope. To test their hypothesis, the authors of this latest study exposed these tiny organisms to high temperatures in artificial sea water that contained only oxygen-18. Using a NanoSIMS (nanoscale secondary ion mass spectrometer), an instrument used to run very small-scale chemical analyses, they then observed the incorporation of oxygen-18 in the calcareous shells. The results show that the level of oxygen-18 present in the foraminifera tests can in fact change without leaving a visible trace, thereby challenging the reliability of their use as a thermometer: “What appeared to be perfectly preserved fossils are in fact not. This means that the paleotemperature estimates made up to now are incorrect,” says Sylvain Bernard, a CNRS researcher at the Paris-based Institute of Mineralogy, Materials Physics and Cosmochemistry and the study’s lead author.

For the French and Swiss team of researchers, rather than showing a gradual decline in ocean temperatures over the past 100 million years, these measurements simply reflect the change in oxygen-18 content in the fossil foraminifera tests. And this change appears to be the result of a process called re-equilibration: during sedimentation, temperatures rise by 20 to 30°C, causing the foraminifera tests to re-equilibrate with the surrounding water. Over the course of some ten million years, this process has a significant impact on paleotemperature estimates, especially those based on foraminifera that lived in cold water. Computer simulations run by the researchers suggest that paleotemperatures in the ocean depths and at the surface of the polar ocean have been overestimated.

For Meibom, the next steps are clear: “To revisit the ocean’s paleotemperatures now, we need to carefully quantify this re-equilibration, which has been overlooked for too long. For that, we have to work on other types of marine organisms so that we clearly understand what took place in the sediment over geological time.” The article’s authors are already hard at work.

原始論文：S. Bernard, D. Daval, P. Ackerer, S. Pont, A. Meibom. Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-01225-9

引用自：Ecole Polytechnique Fédérale de Lausanne. "Current climate change unparalleled over the last 100 million years?." 

在大滅絕造成浩劫之後生物仍持續使海洋生態系運作

原文網址：http://www.leeds.ac.uk/news/article/4121/life_goes_on_for_marine_ecosystems_after_cataclysmic_mass_extinction

在大滅絕造成浩劫之後生物仍持續使海洋生態系運作

科學家發現史上最重大的全球滅絕事件之一並未從基礎層面改變整個海洋生態系。

包括里茲大學的Alex Dunhill博士的國際科學家團隊，發現二疊紀末的大滅絕雖然殲滅了絕大部分的物種，但海洋生態系的運作方式似乎沒有太過劇烈的改變。

主要作者，里茲大學地球和環境學院的Dunhill博士表示：「雖然三疊紀末的大滅絕事件對海洋物種的整體數目有重大影響，但是倖存物種的多樣性仍足以讓海洋生態系的運作方式維持得跟之前一樣。」

「我們並非指說一切安好。」共同作者，德州大學奧斯汀分校地質科學院的古生物學家William Foster表示。「而是滅絕事件過後的全球海洋變得有點像是由骷顱船員掌舵的幽靈船――雖然所有的崗位都在運作，但是僅由少數物種來操縱。」

三疊紀末期的大滅絕事件發生在2億100萬年前。當時火山活動造成大氣的溫室氣體濃度飆升，導致相當迅速的全球暖化，地球將近50%的生物因而死亡。這場火山爆發事件也和盤古超大陸的分裂以及大西洋的形成有關。

團隊檢視了從三疊紀中期至侏儸紀中期7000萬年間的化石紀錄，以比較三疊紀末期滅絕事件發生前後海洋生態系的改變。他們將居住在海洋的動物依據其移動方式、棲息場所和飲食習慣來分類出不同的生活類型。

接著他們確定沒有一種生活類型因為滅絕事件而完全消失，代表海洋生態系完整地保存下來。

他們今日發表在《古生物學》(Palaeontology)的結果顯示雖然滅絕事件並未顛覆全球海洋生態，但它對個別區域和環境卻有深遠的影響，並對特定類型的海洋生態系造成重大衝擊。

Dunhill博士表示：「三疊紀末期死傷最慘重的海洋生物之一便是固定不動，居住在礁體的生物，像是珊瑚。當我們檢視化石紀錄，我們看到雖然海洋生態系整體來說仍然持續運作著，但熱帶珊瑚礁生態系卻耗費超過2000萬年的時間，才從這場環境浩劫中回復過來。」

「礁體生態系對迅速發生的環境變遷最為敏感。三疊紀末期溫室氣體對海洋生態系造成的影響，跟今日我們見到因為海洋溫度升高而死亡的珊瑚礁所經歷的情況並沒有多大差異。」

共同作者，倫敦自然史博物館的Richard Twitchett表示：「瞭解過去大滅絕事件中珊瑚礁的崩毀程度，或許有助於我們預測現在海洋生態系將會遭遇的情況。」

「過去每當溫室氣體迅速增加時，熱帶生態系就會有大範圍地區受到摧殘，儘管各次事件的溫室氣體變化速率和罹難物種不盡相同。雖然(造成二氧化碳增加的)起因有所差異，當看見過往事件一再造成類似的後果，便可以推論類似情形在未來也可能會再度重演。」

Life goes on for marine ecosystems after cataclysmic mass extinction

One of the largest global mass extinctions did not fundamentally change marine ecosystems, scientists have found.

An international team of scientists, including Dr Alex Dunhill from the University of Leeds, has found that although the mass extinction in the Late Triassic period wiped out the vast proportion of species, there appears to have been no drastic changes to the way marine ecosystems functioned.

Lead author Dr Dunhill, from the School of Earth and Environment, said: “While the Late Triassic mass extinction had a big impact on the overall number of marine species, there was still enough diversity among the remaining species that the marine ecosystem was able to function in the same way it had before.”

“We’re not saying nothing happened,” said co-author Dr William Foster, a palaeontologist from the Jackson School of Geosciences at the University of Texas at Austin. “Rather, global oceans in the extinction’s aftermath were a bit like a ship manned by a skeleton crew – all stations were operational, but manned by relatively few species.”

The Late Triassic mass extinction occurred 201 million years ago. Nearly 50 per cent of life on Earth died out as a result of huge volcanic eruptions. The volcanic activity created high levels of greenhouse gases in the atmosphere which led to rapid global warming. The eruptions are also associated with the break-up of the super-continent Pangaea and the opening of the Atlantic Ocean.

The team compared marine ecosystems across the late Triassic mass extinction event by examining fossils from the Middle Triassic to Middle Jurassic —a 70 million-year span. They classified the lifestyle of different ocean-dwelling animals by how they moved, where they lived and how they fed.

They were then able to determine that none of these lifestyles had completely disappeared due to the extinction event, which preserved the marine ecosystem.

Their results, published today in Palaeontology, showed that while the extinction did not result in a global marine ecological shift, it had profound regional and environmental effects and had an extreme impact on specific ocean ecosystems.

Dr Dunhill said: “One of the great marine casualties of the Late Triassic were stationary reef-dwelling animals, such as corals. When we examined the fossil record we saw that while the marine ecosystem continued to function as a whole, it took over 20 million years for tropical reef ecosystems to recover from this environmental cataclysm.

“Reef ecosystems are the most vulnerable to rapid environmental change. The effect of the Late Triassic greenhouse gases on marine ecosystems is not so different from what you see happening to coral reefs suffering from increasing ocean temperatures today.”

Co-author, Professor Richard Twitchett, from the Natural History Museum in London said: “Understanding the extent of reef collapse during past extinctions may help us predict what is in store for our modern marine ecosystems.

“Tropical ecosystems suffered widespread devastation each time that greenhouse gases rose rapidly in the past, despite differences in the rates of change and species involved. When you see similar responses occurring time and time again in the past, despite different starting conditions, it follows that similar responses will likely occur again in the future.”

原始論文：Dunhill, A; Foster, W; Sciberras, J; Twitchett, R. Impact of the Late Triassic mass extinction on functional diversity and composition of marine ecosystems. Palaeontology, 2017 DOI: 10.1111/pala/12332

引用自：University of Leeds. "Life goes on for marine ecosystems after cataclysmic mass extinction." 

它要爆發了嗎？從太空監測火山噴氣

原文網址：http://www.mtu.edu/news/stories/2017/october/gonna-blow-measuring-volcanic-emissions-space.html

它要爆發了嗎？從太空監測火山噴氣

利用NASA衛星測量二氧化碳的結果，可以精確指出排放二氧化碳的人類與火山活動位置，這或許有助於監測造成氣候變遷的溫室氣體變化。

在上個月末，峇里島上的層狀火山――阿貢火山開始冒煙，山下也頻頻發生小型地震。從那時起，當局已經疏散了數千人，避免1963年阿貢火山噴發造成的慘劇再次發生，該次事件造成1000多人死亡。

火山噴發之前通常會有警訊。雖然人類難以感知火山產生的微小地震，但可以藉由地震儀偵測到。此外火山口也會冒出水蒸氣。當火山開始噴出像是二氧化碳和二氧化硫之類的氣體時，代表噴發時刻可能已經迫在眉睫。

但接近火山頂部是項非常危險的作業。利用遙測技術偵測飄往空中的二氧化碳和二氧化硫噴氣，可以在不需冒著生命危險或設備損害的情況下，大幅增進人們對於火山的瞭解。利用遙測系統監控噴氣可以避免人道災難發生，也可以防止發布錯誤的預報。

雖然阿貢火山尚未噴發(在此文章撰寫時)，但地震活動依然劇烈。峇里島當局開始揣測是否真的即將發生火山爆發；從該地區撤離的居民也渴望重回家園，而觀光活動也因此下滑。

包括密西根理工大學的火山學家Simon Carn在內的研究人員，發表了一系列文章詳細描述他們如何利用近地軌道衛星，首次測量人類和自然活動在局部地區排放的二氧化碳，其中包含刊登於期刊《科學》(Science)的論文「Spaceborne detection of localized carbon dioxide sources(利用衛星搭載儀器偵測區域二氧化碳來源)」。

本期《科學》OCO-2特集的五篇論文展現了NASA軌道碳觀測衛星2號(Orbiting Carbon Observatory-2)的能力；以及從衛星搭載感測器的觀測結果，讓我們看見碳如何使地球上的一切事物產生關聯。本研究由NASA噴射推進實驗室資助。

從太空中監測CO₂排放

Carn參與的論文是在討論研究團隊如何運用衛星搭載儀器，以公里為單位對大氣二氧化碳濃度進行高解析度和高靈敏度的測量。資料顯示衛星的感測器可以精確定位出區域大氣二氧化碳的來源。考慮到一開始得先建立的大氣二氧化碳背景值的數據量有多麼龐大，這項成果確實得來不易。

衛星利用其上裝載的光譜儀來進行測量，它可以透過人眼無法見到的光波，對反射光(輻射)進行高光譜解析度的測量。當光線穿過二氧化碳，其中有些波段會被吸收。剩餘的光線碰到海洋和地面後會反射回去。OCO-2的感測器測量反射回來的陽光就可以定量出有多少二氧化碳被吸收，使得科學家可以分離出二氧化碳的排放來源，不管它是人為或自然因素。

「這篇文章的主要重點是我們可以偵測到二氧化碳在小區域的點狀來源，而不是測量大範圍的大氣二氧化碳濃度。」地質與礦業工程科學系的副教授Carn表示，「火山可以成為區域排放二氧化碳的強力來源，但是從全球角度來看，現有證據皆顯示人類排放的二氧化碳比火山多出許多。」

OCO-2衛星的空間解析度為2.25公里，高到化學訊號不會被背景值稀釋。然而，就算OCO-2的測量能力達到空前水準，還是無法用來做為定期監測火山的工具，因為它經過地球同一地區的頻率並不夠頻繁。

Carn表示：「雖然我們證實這項技術確實可以運作，但還是需要更先進的感測器才能讓它成為進行例行性監測的工具，尤其是對於火山這種噴氣成分會迅速變化的地方。如果可以從太空定期監測火山噴出的二氧化碳，對於我們用的這項技術來說是另一項十分有用的附加功能。而且觀察結果立刻就能(在阿貢火山)派上用場。」

Carn徹底檢查衛星載具對二氧化碳的測量結果，來找出其是否有偵測到太平洋島國萬那杜上三座火山噴出的二氧化碳。其中一座雅蘇爾火山至少從1700年代就開始噴發，OCO-2測量當天其噴出的二氧化碳大約比大氣背景值高出3.4 ppm，大致等同於42,000噸。相較之下，人類每天排放的二氧化碳平均為1億噸。

OCO-2的感測器也測量了洛杉磯盆地排出的二氧化碳，結果顯示上方就像有一個二氧化碳「圓穹」籠罩一般。都市地區占了人為排放量的70%以上。

「目前地球的自然作用可以吸收人類燃燒石化燃料而排放的二氧化碳量的一半。」加州帕薩迪納NASA噴射推進實驗室OCO-2科學計畫的副主持人Annmarie Eldering表示。她也是發表在《科學》的OCO-2科學計畫整體現況的論文主要作者。「如果這些自然作用減緩下來，對移除大氣二氧化碳的助益便會減少，由溫室氣體引起的暖化現象就會加速並增強。衛星數據開始讓我們更加認識氣候如何影響碳循環，而減少我們對於兩者未來可能會如何變化的巨大不確定性。」

OCO-2對整個洛杉磯的測量結果精確到可以捕捉城市內部不同排放源的濃度差異。隨著衛星經過擁擠的城市到郊區，再離開至北方人煙稀少的沙漠，他們也跟著描繪出過程中二氧化碳濃度如何逐漸下降。

Is it gonna blow? Measuring volcanic emissions from space

Carbon dioxide measured by a NASA satellite pinpoints sources of the gas from human and volcanic activities, which may help monitor greenhouse gases responsible for climate change.

Late last month, a stratovolcano in Bali named Mount Agung began to smoke. Little earthquakes trembled beneath the mountain. Officials have since evacuated thousands of people to prevent what happened when Agung erupted in 1963, killing more than 1,000 people.

Before volcanoes erupt, there are often warning signs. Tiny earthquakes rarely felt by humans but sensed by seismographs emanate from the volcano. Plumes of water vapor rise from the crater. When the volcano begins to emit gases like carbon dioxide and sulfur dioxide, eruption may be imminent.

But getting close to the top of a volcano is dangerous work. Using remote sensing to detect rising carbon dioxide and sulfur dioxide emissions without endangering people or equipment would greatly increase human understanding of volcanoes. Remote sensing emissions could prevent humanitarian disasters—and false alarms.

Mount Agung hasn’t erupted yet (at the time this article was written), but seismic activity remains intense. Balinese officials are beginning to wonder if an eruption truly is imminent; the people who were evacuated from the area want to return to their homes and tourism is down.

Researchers including Michigan Technological University volcanologist Simon Carn have published a collection of papers including “Spaceborne detection of localized carbon dioxide sources” in the journal Science; the article details the first-known measurement of localized anthropogenic and natural carbon dioxide sources from a satellite in low-Earth orbit.

The five papers in the OCO-2 Science Special Collection showcase the abilities of NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite; measurements from the satellite’s sensors provide insights into how carbon links everything on Earth. The research is supported by NASA’s Jet Propulsion Laboratory.

Monitoring CO₂ Emissions From Space

The paper Carn co-authored discusses how the research team has taken high-resolution, sensitive spaceborne measurements of atmospheric carbon dioxide at the kilometer scale. This data reveals that the satellite’s sensors are able to pinpoint localized sources of carbon dioxide in the atmosphere—a difficult task considering the sheer amount of background carbon dioxide in the atmosphere to begin with.

The satellite uses spectrometry; the sensors onboard the satellite measure reflected sunlight—radiation—in high-spectral resolution using wavelengths undetectable to the human eye. When light passes through carbon dioxide, some is absorbed by the gas. The remaining light bounces off the ocean and the Earth. The OCO-2 sensors measure the light that bounces back to quantify what was absorbed by carbon dioxide, allowing scientists to isolate emission sources, whether human or natural.

“The main focus of the article is detecting localized, point-source emissions of carbon dioxide as opposed to measuring the broad-scale concentration in the atmosphere,” says Carn, an associate professor in the Department of Geological and Mining Engineering and Sciences. “Volcanoes can be strong, localized sources of carbon dioxide. But on a global basis, all available evidence indicates that human activities are emitting much more carbon dioxide than volcanoes.”

The OCO-2 satellite’s spatial resolution—2.25 kilometers—is high enough that chemical signals are not diluted. However, while OCO-2’s measurements are unprecedented, the satellite cannot be used as a routine volcano monitoring tool because it does not pass over the same place on the Earth frequently enough.

“This is a demonstration that the technique does work, but we need better sensors before it becomes a routine monitoring tool, especially for volcanoes where we expect rapid changes in gas emissions,” Carn says. “If we could measure volcanic carbon dioxide from space routinely, it would be a very powerful addition to the techniques we use. That kind of observation would be useful (for Agung) right now.”

Carn combed through satellite data to find detectable spaceborne carbon dioxide measurements from three volcanoes in the Pacific island nation of Vanuatu. One of these, Mount Yasur, has been erupting since at least the 1700s, and on the day of the OCO-2 measurement was emitting carbon dioxide about 3.4 parts per million above background atmospheric levels, equal to about 42 kilotons of emissions. In comparison, human emissions average 100,000 kilotons a day.

OCO-2’s sensors also measured carbon dioxide emissions over the Los Angeles basin, detecting a sort of carbon dioxide “dome”. Urban areas account for more than 70 percent of anthropogenic emissions.

“Natural processes on Earth are currently able to absorb about half of human fossil fuel emissions,” says Annmarie Eldering, OCO-2 deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and lead author of an overview paper in Science on the state of OCO-2 science. “If those natural processes falter, slowing down the helpful removal of carbon dioxide, greenhouse-gas-induced warming would accelerate and intensify. These data begin to give us a better view of how climate affects the carbon cycle, reducing the huge uncertainty around how both might change in the future.”

The OCO-2 measurements across Los Angeles were detailed enough to capture differences in concentrations within the city resulting from localized sources. They also tracked diminishing carbon dioxide concentrations as the spacecraft passed from over the crowded city to the suburbs and out to the sparsely populated desert to the north.

原始論文：Florian M. Schwandner, Michael R. Gunson, Charles E. Miller, Simon A. Carn, Annmarie Eldering, Thomas Krings, Kristal R. Verhulst, David S. Schimel, Hai M. Nguyen, David Crisp, Christopher W. O’Dell, Gregory B. Osterman, Laura T. Iraci, James R. Podolske. Spaceborne detection of localized carbon dioxide sources. Science, 2017; 358 (6360): eaam5782 DOI: 10.1126/science.aam5782

引用自：Michigan Technological University. "Is it gonna blow? Measuring volcanic emissions from space." 

恐龍血液？新研究力勸學者應謹慎看待據稱為軟組織的化石

原文網址：http://www.bristol.ac.uk/news/2017/october/fossilised-soft-tissue.html

恐龍血液？新研究力勸學者應謹慎看待據稱為軟組織的化石

他們的發現證實先前在恐龍化石中保有角蛋白的主張可能有誤。

類似地，他們也證實許多公開發表在骨頭化石中發現的恐龍血液，也可能是有機物分解後的產物，而非真正的血液細胞。

研究人員為了模擬化石在地底深處經歷的狀況，他們在實驗室採取兩種方法進行處理，一種為利用微生物來分解動物組織；另一種則是讓動物組織承受高溫高壓作用，此過程稱為「成熟」(maturation)。

這項刊登於期刊《Palaios》的研究由布里斯托大學地球科學院的Evan Saitta領導。

他表示：「根據角蛋白的種類，它們在腐敗和輕度成熟作用下的分解模式會產生一些結構方面的差異，像是成熟時血液角蛋白會捲曲起來而不像毛髮的角蛋白會變成波浪狀。」

「這些實驗結果或許能讓我們準確辨識出在近代考古遺址中殘留的角蛋白，但是當我們將成熟作用的溫壓因子提高以模擬埋藏作用和化石形成的環境條件，角蛋白會分解成帶有惡臭且可溶於水的液體，使得它們能溶在水裡或是從化石滲漏出去。」

另一項實驗中，他們在真空環境的電子顯微鏡下觀察分解過後的火雞皮，發現表面擁有皺褶、坑洞和圓形凸起，跟之前研究提出為恐龍血液細胞的特徵十分相似。

從實驗和化石中結構的大小和形狀分布可以明顯得知這些結構是經由非生物作用形成，而非細胞生成之類的生物作用。

因此，這些恐龍骨頭中聲稱為血液細胞的物質可能是分解後的有機物。它們有很大機率是微生物入侵到骨頭裡的空腔所造成，並不是容易分解的血液細胞保存格外良好的案例。

Evan Saitta補充：「我們證實不同種類角蛋白的分解模式具有引人注目的差異，或許有助於辨識出考古材料中殘存的角蛋白。」

「然而，當我們模擬經過長時間的形成化石過程和埋藏作用，發現角蛋白會完全分解成容易從化石流失的液體，代表它們在研究古生物遺骸時沒有什麼用途，縱使過往有些研究抱持相反的主張。」

Dinosaur blood? New research urges caution regarding fossilised soft tissue.

Their findings demonstrate that previous claims showing the preservation of keratin protein in dinosaur fossils are likely to be false.

Similarly, widely publicised claims of dinosaur blood in fossil bones were shown to likely represent an artefact of degraded organic matter rather than actual blood cells.

The researchers undertook experimental treatments that either used microbes to decay tissues or subjected tissues to intense heat and pressure – a process known as maturation – in order to mimic the conditions a fossil experiences deep underground.

Evan Saitta from the University of Bristol's School of Earth Science, led the research which has been published in the journal Palaios.

He said: "Decay and mild maturation resulted in some intriguing textural differences in degradation patterns based on the type of keratin such as curling versus crimping of filaments when matured.

"These results may show promise for identifying relatively recent archaeological keratin remains but when maturation conditions are increased to simulate conditions present during burial and fossilisation, the keratin degrades into a foul-smelling, water-soluble fluid that can dissolve or leach away from the fossil."

In another experiment the vacuum conditions of an electron microscope appear to have produced folds, pits and blebs in a sample of degraded turkey skin, similar to those features previously suggested to represent dinosaur blood cells.

The range of sizes and shapes of these experimental and fossil structures is evidence that they form through a non-biological process, as opposed to a biological process like the formation of cells.

Thus, the purported blood cells in these dinosaur bones are likely to be degraded organics, most likely from microbes that invaded the cavities in the bone rather than exceptionally preserved, easily-degradable blood cells.

Evan Saitta added: "We’ve shown that different keratin types show intriguing differences in degradation patterns that might help identify keratinous remains in archaeological material.

"However, when the processes of fossilisation and burial over deep time are simulated, keratin protein fully degrades into a fluid that can be lost from fossils, meaning little utility for studying paleontological remains despite contrary claims."

原始論文：Jakob Vinther et al. Experimental taphonomy of keratin: A structural analysis of early taphonomic changes. Palaios, October 2017 DOI: 10.2110/palo.2017.051

引用自：University of Bristol. "Dinosaur blood? New research urges caution regarding fossilized soft tissue." 

大滅絕造成生物多樣性低落與恐龍統治

原文網址：https://news.ncsu.edu/2017/10/mass-extinctions-led-to-low-species-diversity-dinosaur-rule/

大滅絕造成生物多樣性低落與恐龍統治

Mick Kulikowski

大滅絕是指全世界有超過50%物種滅絕的事件。地球曾經發生過五次大滅絕事件，其中兩次造成僅有少數所謂的「頑強」物種生還，牠們的子嗣在地球從巨變復原的期間往全世界擴散。這項發現或許可以闡明當今物種以極快速率滅絕會如何改變未來的生物族群結構。

北卡羅來納州立大學與北卡羅來納自然科學博物館的獨立博士後研究員David J. Button，和他的同僚仔細觀察2.6億年前至1.75億年前將近900種脊椎生物的化石紀錄，時間橫跨了二疊紀晚期、整個三疊紀至侏儸紀早期。在這段期間發生了兩次大滅絕事件，Button表示兩次滅絕事件之後都產生了類似模式，因此可以推測其他滅絕事件――包括現今正在發生的生物多樣性流失――或許也會造成相同結果。

Button表示：「大滅絕不只會減少動物多樣性，也會影響動物與生態系的分布狀態，也就是生物地理。隨著物種因為滅絕事件消失，牠們的生態棲位也會跟著空缺下來。在滅絕事件過後，空出來的生態棲位會被倖存和新演化出來的『頑強』物種佔據。這些為數不多的生存專家在一時之間迅速擴張並主宰了地球，使得全球生態系變成多樣性低落的『災後動物相』(disaster fauna)。」

水龍獸(Lystrosaurus)是這些生存專家之一，其為一種草食性的哺乳動物近親，體型從狗到豬的大小不等，並且具有獠牙來幫助牠們挖掘植物。

Button表示大約發生在2.52億年前的二疊紀晚期事件使得新的動物族群演化出來，包括最初的恐龍、鱷魚和哺乳類與蜥蜴的近親。而發生在2.01億年前左右的三疊紀晚期事件則殲滅了許多當時生存的主要族群，為恐龍之後接管地球打下了基礎。

「二疊紀晚期的事件造成了90%的海洋生物和70%的陸生脊椎動物滅亡，原因可能是過度活躍的火山活動造成的氣候變遷。當時火山噴濺出大量的玄武岩質岩漿並釋放氣體至大氣當中，使得二氧化碳濃度急遽升高，造成嚴重的暖化與沙漠化。」Button表示，「三疊紀晚期的事件也跟火山活動有所關聯。」

共同作者，伯明罕大學的古生物學教授Richard Butler表示：「大滅絕是種能從基本層面重塑生態系的全球災難。我們的分析提供了重要資料，顯示這類毀滅事件對動物分布的影響和改變有多麼深遠。」

另一位共同作者，阿根廷自然科學博物館的研究人員Martín Ezcurra表示：「化石紀錄讓我們有機會測試演化理論在長時間尺度下的運作情形，這在侷限於現生動植物的演化研究上是無法辦到的。」

Button表示辨認大滅絕事件前後化石紀錄呈現的模式，有助於研究人員預測現今的生物多樣性流失導致的後果。

他補充：「深入瞭解這些過往發生的危難，可以告訴保育人員應該採取何種措施來避免現今的動物遭受類似命運。」

這篇發表於《自然通訊》(Nature Communications)的論文另一位共同作者是里茲大學的Graeme T. Lloyd。本研究的資金來源為新居禮夫人人才培育計畫(編號630123)、歐洲研究委員會創新計劃(編號637483)和青年探索研究獎(編號140101879)。

Mass extinctions led to low species diversity, dinosaur rule

Two of the earth’s five mass extinction events – times when more than half of the world’s species died – resulted in the survival of a low number of so-called “weedy” species that spread their sameness across the world as the Earth recovered from these dramatic upheavals. The findings could shed light on modern high extinction rates and how biological communities may change in the future.

David J. Button, an NC State and North Carolina Museum of Natural Sciences postdoctoral research scholar, and colleagues examined fossil records of almost 900 vertebrate species dating back between 260 and 175 million years ago – from the late Permian through the Triassic and early Jurassic periods. Two mass extinction events occurred during this time. Button says that similar patterns arising after two mass extinctions implies that other extinction events may have the same results – including current biodiversity loss.

“Mass extinctions not only reduced animal diversity, but also affected the distribution of animals and ecosystems, or biogeography,” Button said. “As species are removed by extinction, their ecological niches are left vacant. Following the extinction event, these niches are occupied by surviving and newly evolving ‘weedy’ species. These few generalists spread out and dominated for a time, leading to a low-diversity global ‘disaster fauna.’”

One of these generalists was the Lystrosaurus, a plant-eating early mammal relative that ranged from dog- to pig-sized. It had tusks to help it dig up plant matter.

The late-Permian event – occurring around 252 million years ago – allowed new groups to evolve, including the earliest dinosaurs, crocodiles and relatives of mammals and lizards, Button said. The late-Triassic event, which occurred around 201 million years ago, wiped out many major groups, setting the stage for dinosaurs to take over.

“The late-Permian event caused about 90 percent of sea life and 70 percent of land-living vertebrates to become extinct, probably as a result of climate change from hyperactive volcanism – when volcanoes spewed basalt lava and released gases into the atmosphere causing large increases in carbon dioxide and severe warming resulting in desertification,” Button said. “The late-Triassic event is also associated with volcanism.”

“Mass extinctions were global disasters that fundamentally reshaped ecosystems,” said Richard Butler, professor of palaeobiology at the University of Birmingham and a co-author of the study. “Our new analyses provide crucial data that show just how profoundly these cataclysmic events changed and influenced animal distribution.”

“The fossil record has the potential to test evolutionary hypotheses in long time spans, which is not possible if evolutionary research is limited to living plant and animals,” said Martín Ezcurra, a researcher at the Museo Argentino de Ciencias Naturales who co-authored the paper.

Identifying patterns across mass extinction events in the fossil record can help researchers make predictions about the consequences of current biodiversity loss, Button said.

“Further understanding of these ancient crises will help to inform conservation efforts to prevent modern animals from suffering a similar fate,” he added.

Graeme T. Lloyd of the University of Leeds also co-authored the paper, which is published in Nature Communications. The study was funded by a Marie Curie Actions grant (630123), a European Research Council Starting Grant (637483) and a Discovery Early Career Researcher (DE140101879) award.

原始論文：David J. Button, Graeme T. Lloyd, Martín D. Ezcurra, Richard J. Butler. Mass extinctions drove increased global faunal cosmopolitanism on the supercontinent Pangaea. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-00827-7

引用自：North Carolina State University. "Mass extinctions led to low species diversity, dinosaur rule."