恐龍滅亡都是小行星惹的禍，不干火山的事
By Jim Shelton
耶魯大學地質與地球物理系的助理教授Pincelli
Hull和其同事否定了近期其他幾篇研究。在發表於《科學》(Science)的新研究論文中，他們主張印度德干暗色岩區的大型火山爆發造成的環境衝擊，比6600萬年前的白堊紀―古近紀滅絕事件還要提早許多，因此大滅絕事件並非由其促成。
大多數科學家皆認同這場稱作K-Pg的大滅絕事件是一顆小行星撞擊地球的後果。但因為同一時間點附近有火山活動的跡象，使得有些研究人員也把焦點放在K-Pg事件中火山扮演了什麼樣的角色。
「火山可以引發大滅絕，因為它們會釋放出大量的氣體，像是二氧化碳和二氧化硫，進而改變全世界的氣候並降下酸雨。」此篇新研究的主要作者Hull表示。「但是近期研究都著重在岩漿噴出的時間點，而非氣體釋放的時間點。」
為了定出火山氣體釋放出來的時間點，Hull和她的同事將全球溫度的變化過程、海洋化石的碳同位素(同位素擁有的中子數量比平常的原子更多或更少)，與模型中二氧化碳釋放出來之後對氣候的影響加以比對。他們的結論認為大多數的氣體在小行星撞擊許久之前就已經釋放出來――意謂大滅絕事件是由小行星撞擊獨自造成。
「白堊紀晚期的火山活動造成的暖化事件讓全世界的氣溫逐漸提高了兩度，但是這沒有引發大滅絕事件。」研究中負責彙整溫度記錄，之前任職於耶魯大學的研究人員Michael
Henehan表示。「有些物種因此往南北極遷移，但它們在小行星撞擊許久之前又搬遷回來。」
Hull接著說：「許多人猜測火山對K-Pg來說相當重要，但我們的答案是：『不，火山一點都不重要。』」
最近對印度德干暗色岩的研究顯示K-Pg大滅絕不久之後就發生了大型火山爆發。這項結果讓科學家感到困惑，因為沒有暖化事件可以與之匹配。不過這項新研究也為此謎題給出了可能答案。
「K-Pg滅絕事件的規模相當大，使全球碳循環產生了深遠的改變。」負責進行模擬，耶魯大學的博士後研究員Donald
Penman表示。「我們的結果顯示這些變化會讓海洋長期下來吸收極為大量的二氧化碳，掩蓋了大滅絕事件後的火山活動應該會造成的暖化效應。」
研究共同作者包括德國的André
Bornemann、耶魯大學的研究人員Ellen
Thomas，另外還有來自德國、英國、法國、西班牙、日本、丹麥、美國其他機構的研究人員。
研究經費來自國際海洋發現計畫、美國國家科學基金會與耶魯大學。
In death of dinosaurs, it was all
about the asteroid — not volcanoes
Volcanic activity did not play a direct
role in the mass extinction event that killed the dinosaurs, according to an
international, Yale-led team of researchers. It was all about the asteroid.
In a break from a number of other recent studies,
Yale assistant professor of geology & geophysics Pincelli Hull and her
colleagues argue in a new research paper in Science
that environmental impacts from massive volcanic eruptions in India in the
region known as the Deccan Traps happened well before the Cretaceous-Paleogene
extinction event 66 million years ago and therefore did not contribute to the
mass extinction.
Most scientists acknowledge that the mass extinction
event, also known as K-Pg, occurred after an asteroid slammed into Earth. Some
researchers also have focused on the role of volcanoes in K-Pg due to
indications that volcanic activity happened around the same time.
“Volcanoes can drive mass extinctions because they
release lots of gases, like SO2 and CO2, that can alter
the climate and acidify the world,” said Hull, lead author of the new study.
“But recent work has focused on the timing of lava eruption rather than gas
release.”
To pinpoint the timing of volcanic gas emission, Hull
and her colleagues compared global temperature change and the carbon isotopes
(an isotope is an atom with a higher or lower number of neutrons than normal)
from marine fossils with models of the climatic effect of CO2
release. They concluded that most of the gas release happened well before the
asteroid impact — and that the asteroid was the sole driver of extinction.
“Volcanic activity in the late Cretaceous caused a
gradual global warming event of about two degrees, but not mass extinction,”
said former Yale researcher Michael Henehan, who compiled the temperature
records for the study. “A number of species moved toward the North and South
poles but moved back well before the asteroid impact.”
Added Hull, “A lot of people have speculated that
volcanoes mattered to K-Pg, and we’re saying, ‘No, they didn’t.’”
Recent work on the Deccan Traps, in India, has also
pointed to massive eruptions in the immediate aftermath of the K-Pg mass extinction.
These results have puzzled scientists because there is no warming event to
match. The new study suggests an answer to this puzzle, as well.
“The K-Pg extinction was a mass extinction and this
profoundly altered the global carbon cycle,” said Yale postdoctoral associate
Donald Penman, the study’s modeler. “Our results show that these changes would
allow the ocean to absorb an enormous amount of CO2 on long time
scales — perhaps hiding the warming effects of volcanism in the aftermath of
the event.”
German researcher André Bornemann was co-lead author
of the study. Yale researcher Ellen Thomas was a co-author of the study, along
with additional researchers from institutions in Germany, the United Kingdom,
France, Spain, Japan, Denmark, and the United States.
The International Ocean Discovery Program, the
National Science Foundation, and Yale University helped fund the research.
原始論文：Pincelli M.
Hull, André Bornemann, Donald E. Penman, Michael J. Henehan, Richard D. Norris,
Paul A. Wilson, Peter Blum, Laia Alegret, Sietske J. Batenburg, Paul R. Bown,
Timothy J. Bralower, Cecile Cournede, Alexander Deutsch, Barbara Donner, Oliver
Friedrich, Sofie Jehle, Hojung Kim, Dick Kroon, Peter C. Lippert, Dominik
Loroch, Iris Moebius, Kazuyoshi Moriya, Daniel J. Peppe, Gregory E. Ravizza,
Ursula Röhl, Jonathan D. Schueth, Julio Sepúlveda, Philip F. Sexton, Elizabeth
C. Sibert, Kasia K. Śliwińska, Roger E. Summons, Ellen Thomas, Thomas
Westerhold, Jessica H. Whiteside, Tatsuhiko Yamaguchi, James C. Zachos. On
impact and volcanism across the Cretaceous-Paleogene boundary. Science,
2020 DOI: 10.1126/science.aay5055
引用自：Yale University. "In death of dinosaurs,
it was all about the asteroid -- not volcanoes."
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