在地球歷史四十五億年的歷史當中，最初的十億年左右地球經常受到巨型隕石撞擊。科廷大學的新研究提出了迄今最為有力的證據，指出陸地是由這類撞擊事件所造成。
皮爾巴拉古陸塊
科廷大學地球與行星科學學院的Tim
Johnson博士表示，陸地最初是在巨型隕石撞擊地點形成的想法已經存在了數十年，但是目前為止還沒有太多確切的證據可以支持該理論。
「澳洲西部的皮爾巴拉古陸塊是地球上保存最好的遠古地殼遺骸，透過檢視此處岩石中的微小鋯石晶體，我們發現了這類巨型隕石撞擊的證據，」Johnson博士表示。
「研究鋯石晶體中的氧同位素組成得出了一種『從上到下』的過程，也就是岩石的熔化是從地表附近開始，逐漸往深處進行，這符合巨型隕石撞擊在地質上造成的效應。」
「我們的研究首次提出了強而有力的證據指出以巨型隕石撞擊事件為開端，一連串的過程最終形成了陸地。這種撞擊事件和造成恐龍滅亡的原因很類似，只不過後者比前者晚了數十億年才發生。」
Johnson博士表示了解地球陸地形成以及持續演變的過程相當重要，因為地球大部分生物、所有人類以及地球上幾乎所有的重要礦藏都存在於陸地。
「特別是陸地擁有至關重要的金屬，像是鋰、錫、鎳，這些物資對於新興的綠色科技來說是不可或缺的。我們需要這些科技才能達成減輕氣候變遷的承諾。」
「這些礦藏是地殼分化作用的成果，此作用起始於最早的陸地形成之時，而皮爾巴拉古陸塊只是眾多古陸塊的其中之一。」
「從世界上其他古老大陸地殼的所在區域得到的相關數據，其中的模式也類似於我們在西澳辨識出來的結果。接下來我們想要在這些古老的岩石中測試我們的發現，來看看我們的模型是否如同我們猜測的一樣，可以適用到更廣的範圍。」
Johnson博士的所屬單位為地質科學研究所，是科廷大學最頂尖的地球科學研究單位。
此論文「巨型撞擊事件與陸地的起源及演化」發表於期刊《自然》(Nature)。
Study finds evidence that giant
meteorite impacts created the continents
New Curtin research has provided the
strongest evidence yet that Earth’s continents were formed by giant meteorite
impacts that were particularly prevalent during the first billion years or so
of our planet’s four-and-a-half-billion year history.
Dr Tim Johnson, from Curtin’s School of Earth and
Planetary Sciences, said the idea that the continents originally formed at
sites of giant meteorite impacts had been around for decades, but until now
there was little solid evidence to support the theory.
“By examining tiny crystals of the mineral zircon in
rocks from the Pilbara Craton in Western Australia, which represents Earth’s
best-preserved remnant of ancient crust, we found evidence of these giant
meteorite impacts,” Dr Johnson said.
“Studying the composition of oxygen isotopes in these
zircon crystals revealed a ‘top-down’ process starting with the melting of
rocks near the surface and progressing deeper, consistent with the geological
effect of giant meteorite impacts.
“Our research provides the first solid evidence that
the processes that ultimately formed the continents began with giant meteorite
impacts, similar to those responsible for the extinction of the dinosaurs, but
which occurred billions of years earlier.”
Dr Johnson said understanding the formation and ongoing
evolution of the Earth’s continents was crucial given that these landmasses
host the majority of Earth’s biomass, all humans and almost all of the planet’s
important mineral deposits.
“Not least, the continents host critical metals such
as lithium, tin and nickel, commodities that are essential to the emerging
green technologies needed to fulfil our obligation to mitigate climate change,”
Dr Johnson said.
“These mineral deposits are the end result of a
process known as crustal differentiation, which began with the formation of the
earliest landmasses, of which the Pilbara Craton is just one of many.
“Data related to other areas of ancient continental
crust on Earth appears to show patterns similar to those recognised in Western
Australia. We would like to test our findings on these ancient rocks to see if,
as we suspect, our model is more widely applicable.”
Dr Johnson is affiliated with The Institute for
Geoscience Research (TIGeR), Curtin’s flagship earth sciences research
institute.
The paper, ‘Giant impacts and the origin and
evolution of continents’, was published in Nature.
原始論文：Tim
E. Johnson, Christopher L. Kirkland, Yongjun Lu, R. Hugh Smithies, Michael
Brown & Michael I. H. Hartnady. Giant
impacts and the origin and evolution of continents. Nature, 2022; DOI: 10.1038/s41586-022-04956-y
引用自：Curtin
University. “Study finds evidence that giant meteorite impacts created the
continents.”
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