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”
沒有留言:
張貼留言