恐龍或許是被接連兩下重擊打倒在地的

原文網址：https://around.uoregon.edu/content/one-two-punch-may-have-helped-deck-dinosaurs

恐龍或許是被接連兩下重擊打倒在地的

By Jim Barlow

恐龍到底是被什麼事物消滅的？這項爭議仍然存在。

奧勒岡大學進行的新研究發現6600萬年前沿著深海洋脊發生了跟重力相關的擾動現象，其指出撞擊墨西哥猶加敦半島的巨大隕石可能引發全世界的火山噴出岩漿。這兩次接踵而來的重創或許決定了發生在恐龍身上的噩運。

「我們找到的證據顯示大滅絕事件期間，有段之前未辨識出來的全球火山活動高峰期。」之前在奧勒岡大學就讀博士學位的Joseph Byrnes表示。

這項由Byrnes和奧勒岡大學地球科學系的教授Leif Karlstrom進行的研究於2月7日刊登於《科學進展》(Science Advances)。這份研究詳細描繪了保存在中洋脊(板塊構造在海底的邊界)的火山活動紀錄，證據則來自於從海床上方測到的重力強度變化。

這項奧勒岡大學的研究由美國國家科學基金會資助。Karlstrom表示研究指出在希克蘇魯伯撞擊事件之後全球火山活動有加劇的現象，包括印度德干高原的噴發量也有所提升。位在印度中西部的德干高原是由一段歷時長久的大型火山噴發事件形成，其噴濺出來的熔岩層層堆積達到數千公尺厚，使德干高原成為地球最大型的火山地貌之一。

在恐龍滅絕的爭論中，德干高原地區曾屢次居於要角又退居幕後。科學家知道如此大規模的罕見火山噴發事件對地球氣候造成的擾動足以釀成重大災難，當它們發生時通常會跟大滅絕事件有所關聯。大型火山噴發事件會噴出大量灰燼和氣體至大氣當中，僅有少數植物能生存下來，進而破壞食物鏈造成動物滅絕。

自從在1980年代發現今日墨西哥的希克蘇魯伯附近曾遭到隕石撞擊的證據之後，科學家就一直在爭論殲滅所有非鳥類恐龍的滅絕事件的罪魁禍首到底是誰――隕石還是德干高原噴發事件。

日趨進步的定年方法顯示德干高原的火山在隕石撞擊之前就已經相當活躍。Karlstrom表示隕石撞擊產生傳遍全球的地震波，或許有助於加速這些噴發事件進行。

「我們的成果顯示這些分布在整個地球，極度稀有且破壞性十足的事件彼此之間互有關連。」Karlstrom表示，「隕石撞擊可能影響了正在進行的火山噴發活動，因而對恐龍造成了接連兩下重創。」

2015年加州大學柏克萊分校的研究人員提出這兩個事件可能有關而加強了此種說法。包括Karlstrom的該團隊認為隕石產生的強力地震波撼動了整個地球，或許能影響遠方的火山活動。

Karlstrom表示就像平常由構造活動產生的地震有時候會讓水井和溪流的流量增加，他們的研究認為震波產生的晃動可以使德干高原下方地函儲存的岩漿釋放出來，而在當地造成最具規模的火山爆發。

奧勒岡大學進行的這項新發現將震波引起噴發的發生範圍從印度拓展至全世界的海盆。

現為明尼蘇達大學博士後研究員的Byrnes從公開取用的資料庫分析全球自由空間重力、海底地形和板塊擴張速率的資料。

在他的分析當中，他以一百萬年為區間來劃分海床年代，建構出的紀錄可以回推至1億年前。他發現大約6600萬年前，自由空間重力的數據出現異常的頻率有所增加，顯示沿著古代洋脊發生的海底岩漿活動此時出現了短暫的高峰期。

自由空間重力異常是指重力加速度的變化量，計算單位是相當微小的毫伽。地球重力比較強的地方會聚集更多海水，運用衛星測量便能偵測到此種變化。Byrnes發現在隕石撞擊過後的首個100萬年之內形成的海床，其自由空間重力發生了5到20毫伽的異常變化。

A one-two punch may have helped deck the dinosaurs

The debate goes on: What killed off the dinosaurs?

New University of Oregon research has identified gravity-related fluctuations dating to 66 million years ago along deep ocean ridges that point to a “one-two punch” from the big meteor that struck off Mexico’s Yucatan peninsula, possibly triggering a worldwide release of volcanic magma that could have helped seal the dinosaurs' fate.

"We found evidence for a previously unknown period of globally heighted volcanic activity during the mass-extinction event," said former UO doctoral student Joseph Byrnes.

The study by Byrnes and Leif Karlstrom, a professor in the UO’s Department of Earth Sciences, was published Feb. 7 in Science Advances. It details a record of volcanism preserved along the mid-ocean ridges, which mark the oceanic boundaries of tectonic plates. The evidence comes from changes in the strength of gravity above the seafloor.

The findings of the UO's National Science Foundation-supported study, Karlstrom said, point to a pulse of accelerated worldwide volcanic activity that includes enhanced eruptions at India's Deccan Traps after the Chicxulub impact. The Deccan Traps, in west-central India, formed during a period of massive eruptions that poured out layers of molten rock thousands of feet deep, creating one of the largest volcanic features on Earth.

The Deccan Traps region has been in and out of the dinosaur debate. Rare volcanic events at such a scale are known to cause catastrophic disturbances to Earth's climate, and, when they occur, they are often linked to mass extinctions. Huge volcanic events can eject so much ash and gas into the atmosphere that few plants survive, disrupting the food chain and causing animals to go extinct.

Since evidence of the meteor strike near present-day Chicxulub, Mexico, surfaced in the 1980s, scientists have debated whether the meteor or the Deccan Traps eruptions drove the extinction event that killed off all nonavian dinosaurs.

Progressively improving dating methods indicate that the Deccan Traps volcanoes already were active when the meteor struck. Resulting seismic waves moving through the planet from the meteor strike, Karlstrom said, probably fueled an acceleration of those eruptions.

"Our work suggests a connection between these exceedingly rare and catastrophic events, distributed over the entire planet," Karlstrom said. "The meteorite's impact may have influenced volcanic eruptions that were already going on, making for a one-two punch."

That idea gained strength in 2015 when researchers at the University of California, Berkeley, proposed that the two events might be connected. That team, which included Karlstrom, suggested that the meteorite may have modulated distant volcanism by generating powerful seismic waves that produced shaking worldwide.

Similar to the impacts that normal tectonic earthquakes sometimes have on wells and streams, Karlstrom said, the study proposed that seismic shaking liberated magma stored in the mantle beneath the Deccan Traps and caused the largest eruptions there.

The new findings at the UO extend this eruption-triggering in India to ocean basins worldwide.

Byrnes, now a postdoctoral researcher at the University of Minnesota, analyzed publicly available global data sets on free-air gravity, ocean floor topography and tectonic spreading rates.

In his analyses, he divided the seafloor into 1-million-year-old groupings, constructing a record back to 100 million years ago. At about 66 million years, he found evidence for a "short-lived pulse of marine magmatism" along ancient ocean ridges. This pulse is suggested by a spike in the rate of the occurrence of free-air gravity anomalies seen in the data set.

Free-air gravity anomalies, measured in tiny increments call milligals, account for variations in gravitational acceleration, found from satellite measurements of additional seawater collecting where the Earth's gravity is stronger. Byrnes found changes in free-air gravity anomalies of between five and 20 milligals associated with seafloor created in the first million years after the meteor.

原始論文：Joseph S. Byrnes, Leif Karlstrom. Anomalous K-Pg–aged seafloor attributed to impact-induced mid-ocean ridge magmatism. Science Advances, 2018; 4 (2): eaao2994 DOI: 10.1126/sciadv.aao2994

引用自：University of Oregon. "A one-two punch may have helped deck the dinosaurs.”

古代多峇火山的爆發並未在東非造成火山冬天

原文網址：https://uanews.arizona.edu/story/no-volcanic-winter-east-africa-ancient-toba-eruption

古代多峇火山的爆發並未在東非造成火山冬天

亞利桑那州立大學的地質學家表示，74000年前的超級火山爆發並未在東非引發造成人類數目減少的嚴重環境破壞。

根據亞利桑那州立大學的地質學家所述，大約74000年前發生在蘇門答臘的多峇超級火山爆發並未在東非造成長達6年的「火山冬天」，故該地區的人口也沒有因此而急速下降。

這項新發現駁斥了多峇巨災理論(Toba catastrophe hypothesis)。該理論認為火山噴發和後續效應使東非陷入了數年的酷寒，造成嚴重的生態浩劫。

「這是首度有研究提供直接證據顯示噴發不久之前和之後的植被狀況，進而指出多峇火山爆發對植被的影響。」主要作者，亞利桑那州立大學地質科學系的博士候選人Chad L. Yost表示。「對於東非的植被生長狀況來說，多峇火山爆發並未造成顯著的負面衝擊。」

利用沖刷至湖泊然後堆積在湖底的植物部件，研究人員可以重建某個地區過往的生態系樣貌。Yost和同事研究的微小植物碎屑保存於馬拉威湖的兩根沉積物岩芯當中，這座湖泊長約570公里，是東非大裂谷最南端的湖泊。

之前的研究曾在馬拉威湖的岩芯當中找到來自於多峇火山爆發的物質，它們可以指出噴發時間並讓Yost和同事得以追溯多峇火山爆發之前100年和之後200年間發生的事物。研究團隊在這300年區間中，平均每隔8.5年便分析一個代表性樣品。

「結果相當令人驚訝。」Yost表示。「基於多峇火山爆發的規模，你可能會預料有嚴重的冷化現象發生――但我們卻沒有看到。」

Yost和他的同事並未看到低海拔的植被在噴發過後有顯著變化，但團隊確實發現噴發剛結束時，某些山區植物有消失的跡象。他說噴發造成的冷化可能對不耐寒的植物造成了損害。

Yost表示如果此區域在多峇火山噴發之後歷經了長達數年的嚴重冷化，則岩芯呈現的證據應該會指出該區域各海拔的植被都經歷了大規模死亡。

多峇巨災理論中的一部份認為該次噴發造成人類數目大幅減少。

「我們知道當時馬拉威湖周遭的50公里以內有解剖學上的現代人生活著，」Yost表示。「人類或許可以搬遷到其他棲地或者低海拔地區，多峇火山爆發造成的冷化效應對這些地方只有些微影響或者根本沒有。」

他說該地區已知的多數考古場址都是位在低海拔地區而非山區。

共同作者，亞利桑那州立大學地質科學系的特聘教授 Andrew S. Cohen表示：「發生在地球歷史75000年前的單一事件，造成人類搖籃的人口數大幅縮減的說法並不成立。」

研究團隊的論文「Subdecadal phytolith and charcoal records from Lake Malawi, East Africa imply minimal effects on human evolution from the ~74 ka Toba supereruption」本周發表在《人類演化期刊》(Journal of Human Evolution)。

和Yost與Cohen's共同進行研究的作者包括德州大學奧斯汀分校的Lily J. Jackson和印第安納州立大學的Jeffery R. Stone。資金來源則是美國國家科學基金會和國際陸地科學鑽探計畫。

Cohen是馬拉威湖鑽探計畫的主要研究人員之一，他說這項合作計畫於2005年從湖底成功取出了岩芯。馬拉威湖是地球上最深的湖泊之一，其岩芯所保存的物質紀錄可以追溯至超過100萬年以前。

沖刷至湖裡的動植物組織會一年一年地層層堆積在湖底，因此湖泊本身和周遭陸地的過往環境變化會被記錄在沉積物岩芯當中。

Yost的研究取自於湖泊的兩根岩芯：一根來自靠近山區的湖泊北端，另一根則是在湖泊的中心地帶。Cohen表示過往其他研究人員已經精確指出岩芯中的哪個層位含有來自多峇火山爆發的玻璃質和晶體。

Yost從岩芯中取出橫跨火山爆發前後區段的樣品，並分析其中的木炭以及含有矽質的植物組織――植矽體(phytolith)。

Yost的專長為辨識特定植矽體是來自於何種植物，他說這項研究需要盯著顯微鏡數百個小時才得以完成。

如果多峇巨災理論為真，那麼大規模死亡的植被應該會使野火的發生次數增加，造成更多木炭被沖刷到湖裡。然而，他在噴發之後堆積的沉積物中，並沒有觀察到木炭數量增加至超過正常變動範圍之外。

「我們判定多峇火山爆發對生長在東非的植被並沒有造成重大的負面影響，」Yost表示。「我們希望這項結果可以成為宣告多峇巨災理論為錯誤的關鍵證據。」

No Volcanic Winter in East Africa From Ancient Toba Eruption

The supereruption 74,000 years ago did not trigger major environmental disruption that caused human populations in East Africa to decline, UA geoscientists say.

The massive Toba volcanic eruption on the island of Sumatra about 74,000 years ago did not cause a six-year-long "volcanic winter" in East Africa and thereby cause the human population in the region to plummet, according to new research from University of Arizona geoscientists.

The new findings disagree with the Toba catastrophe hypothesis, which says the eruption and its aftermath caused drastic, multiyear cooling and severe ecological disruption in East Africa.

"This is the first research that provides direct evidence for the effects of the Toba eruption on vegetation just before and just after the eruption," said lead author Chad L. Yost, a doctoral candidate in the UA Department of Geosciences. "The Toba eruption had no significant negative impact on vegetation growing in East Africa."

Researchers can use ancient plant parts that wash into and accumulate on the bottoms of lakes to reconstruct a region's past ecosystem. Yost and his colleagues studied microscopic bits of plants preserved in two sediment cores from Lake Malawi, which is approximately 570 kilometers (354 miles) long and is the southernmost of the East African Rift lakes.

Previous investigators found material from the Toba eruption in the Lake Malawi cores. That material pinpoints the time of the eruption and allowed Yost and colleagues to peer back in time 100 years before to 200 years after the Toba eruption. The team analyzed samples that represented, on average, every 8.5 years within that 300-year interval.

"It is surprising," Yost said. "You would have expected severe cooling based on the size of the Toba eruption — yet that's not what we see."

Yost and his colleagues did not find marked changes in lower-elevation vegetation post-eruption. The team did find some die-off of mountain plants just after the eruption. Cooling from the eruption might have injured frost-intolerant plants, he said.

Had the region experienced the drastic, multiyear cooling post-Toba, the cores would have evidence of a massive die-off of the region's vegetation at all elevations, Yost said.

Part of the Toba catastrophe hypothesis suggests the eruption caused human populations to shrink.

"We know anatomically modern humans were living within 50 kilometers of Lake Malawi," Yost said. "People would have been able to travel to habitats and lower elevations that had little to no cooling effect from the Toba eruption."

Most of the region's known archaeological sites are from low elevations, not the mountains, he said.

Co-author Andrew S. Cohen, UA Distinguished Professor of Geosciences, said, "That a singular event in Earth history 75,000 years ago caused human populations in the cradle of humankind to drop is not a tenable idea."

The team's paper, "Subdecadal phytolith and charcoal records from Lake Malawi, East Africa imply minimal effects on human evolution from the ~74 ka Toba supereruption," is published online this week in the Journal of Human Evolution.

Yost's and Cohen's co-authors are Lily J. Jackson of the University of Texas, Austin, and Jeffery R. Stone of Indiana State University. The National Science Foundation and the International Continental Scientific Drilling Program funded the research.

The Lake Malawi Drilling Project took the cores from the lake bottom in 2005, said Cohen, one of the principal investigators on the collaborative project. The lake is one of the deepest in the world. The material archived in the cores goes back more than 1 million years.

Plant and animal material washes into lakes and is deposited on the bottom in annual layers, so a sediment core contains a record of the past environments of a lake and of the surrounding land.

Yost studied two cores taken from the lake: one from the north end of the lake, which is closer to the mountains, and the other from the central part of the lake. Other researchers had pinpointed what layer in those cores had glass and crystals from the Toba eruption, Cohen said.

Yost took samples from the cores that straddled the eruption and analyzed the samples for charcoal and for silica-containing plant parts called phytoliths.

The work required hundreds of hours of peering through a microscope, said Yost, an expert in identifying the type of plant a particular phytolith came from.

If the Toba catastrophe hypothesis is true, the massive die-off of vegetation would have resulted in more wildfires and therefore more charcoal washing into the lake. However, he did not find an increase in charcoal outside the range of normal variability in the sediments deposited after the eruption.

"We determined that the Toba eruption had no significant negative impact on vegetation growing in East Africa," Yost said. "We hope this will put the final nail in the coffin of the Toba catastrophe hypothesis."

原始論文：Chad L. Yost, Lily J. Jackson, Jeffery R. Stone, Andrew S. Cohen. Subdecadal phytolith and charcoal records from Lake Malawi, East Africa imply minimal effects on human evolution from the ∼74 ka Toba supereruption. Journal of Human Evolution, 2018; 116: 75 DOI: 10.1016/j.jhevol.2017.11.005

引用自：University of Arizona. "No volcanic winter in East Africa from ancient Toba eruption." 

變動的氣候―過去與未來

原文網址：https://www.awi.de/nc/en/about-us/service/press/press-release/klimaschwankungen-in-vergangenheit-und-zukunft.html

變動的氣候―過去與未來

研究人員比較冰河期和間冰期的全球氣溫變化程度

若想知道未來氣候會如何變化，就必須先回首過去。透過觀察數千年以前發生的氣候變遷，我們可以更加改進對未來氣候的預測。研究人員比較冰芯樣本和海洋沉積物的各個層位，可以推導出地球的平均氣溫如何隨著時間變化以及變動程度有多大諸如此類的氣候因子。從2萬1000年前的末次冰河期高峰到現在我們所處的間冰期，地球整體的暖化程度平均而言為5℃。有鑒於全球暖化會持續至未來，對現今地球的全體居民來說，知道將來的溫度上升會穩定成長或者突然飆高是相當重要的一件事。此外，對於氣候變遷的調適措施來說極端事件的頻率是規劃時必要的基準值，因為當對象為防洪措施、運輸系統和建築材料時，我們要防範的不僅是「平均」變化，還必須考慮到最糟的情況。

德國波茨坦的阿爾弗雷德˙魏格納極地與海洋研究所(AWI)中的亥姆霍兹青年研究員小組ECUS的氣候學家，探討隨著地球從末次冰河期進入到現今間冰期，全球氣溫的變化幅度是如何跟著改變。目前為止科學家推測氣溫的變化程度在末次冰河期期間較為劇烈，而現今間冰期大部分時候的溫度變化都比較和緩。此解釋的基礎為格陵蘭中部冰芯的水同位素資料。

由Kira Rehfeld博士和Thomas Laepple博士領導的團隊比較了格陵蘭(冰芯)的數據、採集自世界各地數個海域的沉積物數據，還有從南極取得的冰芯樣品。他們證實冰河期溫度劇烈波動的現象在全世界的表現絕非一致，而是各地皆有不同。比方說，末次冰河期高峰時熱帶的溫度變化比現今還要強烈三倍，而格陵蘭的冰芯則顯示當地的變動幅度比現今還要強個70倍。「格陵蘭的冰芯無疑是瞭解過往氣候的重要鑰匙。話雖如此，我們的研究證明從格陵蘭冰芯得出的結論並非總是能代表整個世界。」主持青年研究員小組的Laepple如此解釋。他同時也是歐洲研究委員會資助的青年研究小組SPACE的主持人。

第一作者Kira Rehfeld和其同僚的成果為首次彙整並比較總計來自99個研究地點的不同類型氣候資料。在氣侯學界，冰芯通常被視為黃金標準，因為它的分層相當分明且連續，不像從海床取出的沉積物時常受到構造運動、洋流或海洋生物影響導致層狀構造毀損。AWI的研究人員設計出某些運算方法使他們在計算不同類型的古氣候資料時，可以估計各類資料的不確定因素和可能誤差來源，並將這些因子納入他們的分析當中。Laepple表示：「如此這般，我們可以比較地球歷史上不同時期的沉積物樣品和冰芯。」

在冰河期因為被冰層覆蓋的極區和熱帶地區的溫差更為巨大，造成冷暖氣團之間的能量流動更為活躍，使得冰河期的溫度變化比較強烈。「若我們依循此想法的邏輯便可以得到此結論：隨著全球暖化加劇，溫度變化幅度會持續減小。」Rehfeld表示這單純是因為北地暖化後跟熱帶之間的溫差會縮小。「然而，我們資料的時間單位一格便涵蓋數個世紀至數千年――也就是我們的視野無法聚焦至數年之間，代表在論及決定天氣的極端事件時，我們只能透過間接方法歸納出結論。」目前在英國南極調查局進行研究的氣候學者Rehfeld解釋。

進行氣候模擬的研究人員先前於2014年提出一套假說，來解釋在溫暖氣候條件下氣溫變動幅度會降低的機制。但直到現在Rehfeld、Laepple 和其同僚才首度利用過往的全球氣候資料來佐證這套理論。AWI的研究人員接著描述了他們的下個目標：「我們的計劃是詳細研究短期的氣溫變化在過去是如何隨著時間改變，以及和長期氣候變遷的關係為何。為了達成這項目標，我們需要更為可靠的氣候紀錄，並增進我們對它們運作方式的理解。」要把古氣候紀錄的準確度提升至可以同時反映極端事件的水準，可能會是未來數年最大的挑戰之一。

Climate variability – past and future

Researchers compare global temperature variability in glacial and interglacial periods

If you want to know how the climate will change in the future, you need to look at the past. By looking at the climate changes that took place thousands of years ago, we can improve predictions for future climate. Comparing layers in the ice-core samples and ocean sediments has allowed researchers to deduce e.g. how the average temperature on Earth has changed over time, and also how great the variability was. From the height of the last glacial period 21,000 years ago to our current interglacial period, the Earth has warmed by an average of five degrees Celsius. In view of future global warming, it’s vital for today’s global population to know whether temperatures will rise steadily, or whether there will be sudden, major fluctuations. The frequency of extreme events represents an essential benchmark for climate change adaptation measures, since, when it comes to flood protection, transport and building materials, we need to be prepared for the worst-case scenario, and not just for “average” changes.

Climate researchers from the Helmholtz Young Investigators Group ECUS at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Potsdam have now investigated how temperature variability changed as the Earth warmed from the last glacial period to the current interglacial period. To date it has been assumed that temperatures varied greatly during the last glacial, while the current interglacial was largely characterised by small temperature variations. This interpretation was based on water isotope data from central Greenland ice cores.

The team, led by Dr Kira Rehfeld and Dr Thomas Laepple, compared the Greenland data with that from sediments collected in several ocean regions around the globe, as well as from ice-core samples gathered in the Antarctic. They demonstrate that the phenomenon of major temperature fluctuations during glacial periods has by no means manifested uniformly worldwide, but has instead varied from region to region. For instance, in the Tropics the temperature variations were three times as intense as today at the height of the last glacial, whereas the ice cores from Greenland indicate variations that were 70 times as intense. “The ice cores from Greenland are without a doubt an important key to understanding the climate of the past. That being said, our study confirms that the conclusions regarding Greenland aren’t always representative of the entire world,” explains Young Investigators Group leader Laepple, who also heads the ERC-funded Young Investigators Group SPACE.

The achievement of first author Kira Rehfeld and her colleagues: they have for the first time gathered and compared data from diverse climate archives and a total of 99 research sites. In the climate research community, ice cores are generally considered the gold standard, because their layers are highly consistent, unlike sediment layers from the seafloor, which are frequently marred by tectonic shifts, currents or marine organisms. The AWI researchers have devised mathematical methods that allow them to estimate the uncertainties and potential sources of error while assessing various paleoclimate archives, and to take these factors into account in their analyses. “As such, we can compare the sediment samples with the ice cores for various epochs in the planet’s history,” says Laepple.

The more intensive variations during glacial periods are due to the greater difference in temperature between the ice-covered polar regions and the Tropics, which produced a more dynamic exchange of warm and cold air masses. “If we then follow that idea to its logical conclusion, it tells us the variations will continue to lessen as global warming progresses,” says Rehfeld – simply because the difference in temperature between the warming North and the Tropics will decline. “However, our data covers timeframes spanning centuries and millennia – we can’t zoom in on just a handful of years, which means we can only draw indirect conclusions regarding the extreme events that shape weather,” explains climate researcher Rehfeld, who is currently pursuing research with the British Antarctic Survey (BAS).

Climate modellers had previously postulated the mechanism of reduced variability under warmer climatic conditions in 2014. Yet with their analysis, Rehfeld, Laepple and colleagues are the first to reinforce this theory with global climate data from the past. The AWI researchers describe their next endeavour as follows: “We plan to investigate in detail the changes in short-term variations in the past and their relation to long-term climate changes. To do so, we need reliable climate archives, and to improve our understanding of how they work.” Increasing the accuracy to a level at which paleo-archives can also reflect extreme events will likely be one of the greatest challenges for the years to come.

原始論文：Kira Rehfeld, Thomas Münch, Sze Ling Ho, Thomas Laepple. Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene. Nature, 2018; DOI: 10.1038/nature25454

引用自：Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. "Climate variability -- past and future."

地球的中年危機：新研究支持地質紀錄中確實有一段「呆滯」時期

原文網址：http://news.curtin.edu.au/media-releases/earths-mid-life-crisis-new-research-backs-lull-geologic-record/

地球的中年危機：新研究支持地質紀錄中確實有一段「呆滯」時期

柯廷大學最近公開的新研究結果，支持地球的歷史進程在22億到23億年前曾經歷一段「地質停滯期」的說法。

科學家對於地質歷史中「古元古代」(Palaeoproterozoic)這段時期發生了什麼樣的地質作用有所分歧，而今日刊登於《自然―地質科學》(Nature Geoscience)的研究可能會重新點燃科學家對於地球歷史進程的爭論。

主要作者，柯廷大學地質與行星科學院的Christopher Spencer博士表示，從研究中得出的發現指出這段時期陸地的岩漿作用近乎完全停擺，而對我們今日所知的地質紀錄具有深遠影響。

Spencer表示：「我們的研究顯示出地質記錄在古元古代確實有段空白，這段時期不只火山爆發的數目有所下降，沉積速率也減緩下來，板塊運動也明顯遲緩許多。」

「古元古代早期是地球歷史上的一個關鍵時期。在這段時期首度有微量氧氣進入大氣當中，並且發生了第一起覆蓋全球的冰河事件。但實際上其他地質作用在此時也停頓了下來，幾乎就像是地球經歷了一場中年危機一樣。」

研究彙整了大量現有的地質數據，並分析從澳洲西部斯特靈山脈、中國、加拿大北部和非洲南部採集的岩石。

Spencer博士表示：「我們彙集的岩石和數據越多，就更加清楚地顯示這段時期保存的紀錄非常少。」

「地球過去的地函溫度比現在熾熱許多，隨著時間流逝火山會讓地函降溫，而一般認為地質作用也會跟著和緩下來。我們認為持續和緩的地質作用造成了我們在古元古代早期看見的劇烈地質變化。」

「這段『休眠期』持續了大約1億年，我們認為它在地質歷史中留下的最明顯標記，是板塊構造運動從『遠古型』轉變成類似今日運作的『現代型』。在這段休眠之後，地質歷史於大約22億至20億年前開始重新『醒來』，點燃了火山活動並讓大陸地殼的成分發生變化。」

Spencer博士相信這些發現可以讓我們對世界上的自然資源以及它們的分布位置有更多認識，也顯示這段時期還需要進行更多研究，以更加確認地球的地質作用當時受到了什麼影響。

完整研究論文刊登於《自然―地質科學》。

Earth’s mid-life crisis – new research backs ‘lull’ in the geologic record

New research backing claims that the Earth experienced a ‘geological lull’ in its development around 2.3 to 2.2 billion years ago has just been released by Curtin University.

Published today in Nature Geoscience, the research is likely to re-ignite debate over the Earth’s development, with scientists divided over what geologic processes occurred during the Palaeoproterozoic geologic era.

Lead researcher Dr Christopher Spencer from the School of Earth and Planetary Sciences at Curtin University said the research findings point to a near complete shutdown of continental magmatism during this period, and has profoundly shaped the geologic record as we know it today.

“Our research shows a bona fide gap in the Palaeoproterozoioc geologic record, with not only a slowing down of the number of volcanoes erupting during this time, but also a slow-down in sedimentation and a noticeable lull in tectonic plate movement,” Dr Spencer said.

“The early Paleoproterozoic was a significant time in Earth history. It was at this time when the atmosphere got its first whiff of oxygen and also the first global glaciation event. But this was also a period where other geologic processes effectively shut down. It’s almost as if the Earth experienced a mid-life crisis.”

The research involved compiling massive amounts of existing geological data as well as examination of rocks collected in Western Australia’s Stirling Ranges, China, Northern Canada and Southern Africa.

 “The more rocks and data we collected the clearer it is that there is very little preserved record for this period,” Dr Spencer said.

 “Earth’s mantle used to be much hotter than it is today and over time volcanoes allowed the mantle to cool and geologic processes are thought to have slowed down. We believe this continual slowdown led to dramatic geological changes such as those seen in the early Paleoproterozoic.

“This ‘dormant’ period lasted around 100 million years and signalled what we believe was a shift from ‘ancient-style’ tectonics to ‘modern-style’ tectonics more akin to those operating in the present day. Following this dormant period Earth’s geology started to ‘wake-up’ again around 2.2 to 2.0 billion years ago with a ‘flare-up’ of volcanic activity and a shift in the composition of the continental crust.”

Dr Spencer believes these findings could provide greater insight into our understanding of the world’s natural resources and where they exist, and has suggested more research is now needed into this time period to better determine how the earth’s geological processes were impacted.

The full research paper has been published in Nature Geoscience.

原始論文：Christopher J. Spencer, J. Brendan Murphy, Christopher L. Kirkland, Yebo Liu, Ross N. Mitchell. A Palaeoproterozoic tectono-magmatic lull as a potential trigger for the supercontinent cycle. Nature Geoscience (2018). DOI: 10.1038/s41561-017-0051-y

引用自：Curtin University. “Earth’s mid-life crisis – new research backs ‘lull’ in the geologic record”