遠古氣泡改寫了地球大氣氣含量的歷史

原始網址：www.sciencedaily.com/releases/2016/08/160822174234.htm

Ancient air pockets changing the history of Earth’s oxygen

遠古氣泡改寫了地球大氣氣含量的歷史

Ancient air trapped in rock salt for 813 million years is changing the timeline of atmospheric changes and life on Earth.

8.13億年前包裹在岩鹽當中的遠古空氣改寫了地球大氣組成及生命演化歷程的時間線

Defining past atmospheric compositions is an important yet daunting task for geologists. Most methods for determining past Earth surface conditions rely on indirect proxies gleaned from ancient sedimentary rocks. Further complicating matters, sedimentary rocks are notoriously difficult to date because they contain remnants of other rocks formed at various times.

對於地質學家來說界定過去大氣的組成是項重要，卻也相當棘手的課題。在界定地表環境因子過去的狀態時，地質學家用的多數方法都仰賴從古代沉積岩當中蒐羅間接代用指標。讓事情變得更複雜的是，由於沉積岩內有其他形成於不同年代的岩石碎屑殘留其中，造成沉積岩的年代是出了名的難以準確定出。

As a result, oxygenation, or the rise of oxygen in the Earth's atmosphere, has been presumed to occur about 550 million years ago near the boundary between the Precambrian and Paleozoic geologic periods.

過往研究推測地球大氣氧化，也就是氧氣含量提升的時間點大約是在5.5億年前，在地質史上是前寒武紀跟古生代的交接處附近。

West Virginia University geologist Kathleen Benison is part of a research team using new direct methods to measure the Earth's oxygenation.

西維吉尼亞大學的地質學家 Kathleen Benison所屬的研究團隊，利用新的研究方法而能夠直接測量遠古地球大氣的氧含量。

The team's study identifies, for the first time, exactly how much oxygen was in Earth's atmosphere 813 million years ago -- 10.9 percent. This finding, they say, demonstrates that oxygenation on Earth occurred 300 million years earlier than previously concluded from indirect measurements.

這個團隊的研究首次分辨出8.13億年前地球大氣究竟含有多少比例的氧氣，答案是百分之10.9。研究人員說這項發現顯示地球大氣發生氧化的時間，較過往從間接證據歸納出的年代還要早了3億年。

"Diversity of life emerges right around this time period," Benison said. "We used to think that to have diversity of life we needed specific things, including a certain amount of oxygen. (The findings) show that not as much oxygen is required for organisms to develop."

「生命發生多樣化的時間點也是在這段時期(指5.5億年)附近，」 Benison說。「以前我們認為生命多樣化需要某些特別的條件才能發生，像是氧氣提升到一定含量。(這項發現)卻顯示生命要迅速發展並不需要很多的氧氣。」

Fluid inclusions, the microscopic bubbles of liquids and gases in rock salt, can contain trapped air. Analysis of this trapped air allows researchers to understand past surface conditions and how oxygen has changed over the course of geologic history.

岩鹽當中的流體包裹體(inclusion)，也就是微小的氣泡或水泡可以捕獲形成當時的空氣。分析這些被困住的氣體可以讓研究人員瞭解在地質史的進程當中，過往的地表環境因子及大氣氧含量是如何變化。

The team used a quadrupole mass spectrometer to study the air pockets. Carefully crushing minute rock salt crystals released water and gases into the mass spectrometer, which then analyzed for various compounds of oxygen and other gases.

研究團隊利用四極柱式質譜儀(quadrupole mass spectrometer )來分析這些氣泡。研究人員先仔細磨碎細小的岩鹽晶體以將其中含有的水分和氣體釋放到質譜儀當中，接著就能利用質譜儀分析氧氣以及其他各種氣體分子的含量。

"There are a lot of different environmental conditions specific from the past that we can find occurring in modern samples," Benison said. "This tells us about the range of conditions on Earth and also has implications for Mars."

「我們可以從現今的樣品發現過往的環境因子特性彼此之間有很大的差異，」 Benison說。「這告訴我們地球環境因子的變化範圍可以有多廣，甚至能運用到火星的研究中。」

引用自：West Virginia University - Eberly College of Arts and Sciences. "Ancient air pockets changing the history of Earth’s oxygen." ScienceDaily. ScienceDaily, 22 August 2016. 

論文來源Nigel J.F. Blamey, Uwe Brand, John Parnell, Natalie Spear, Christophe Lécuyer, Kathleen Benison, Fanwei Meng, Pei Ni. Paradigm shift in determining Neoproterozoic atmospheric oxygen. Geology, 2016; 44 (8): 651