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Science & technology
科技版塊
Forming continents
形成大陸
Impact creator
撞擊的創造者
Earth may have been shaped by forces from outer space
地球可能是由外太空的力量塑造的
The earth is a poor archivist.
地球是一個糟糕的檔案保管員。
The rigid tectonic plates of its outer layers are continuously in motion, sliding over one another to swallow almost all records of the past, melting them into the mantle and then casting them anew.
剛性板塊不斷運動，相互滑動，吞噬了幾乎所有過去的記錄，將它們熔化到地幔中，然后重新澆鑄。
This makes it difficult to reconstruct the 4.5bn-year-old planet’s formative years.
這使得很難重建這顆有45億年歷史的行星的形成期。
A particular problem is the crucial biographical detail of how the first continents came to be.
一個特別的問題是關于第一個大陸是如何形成的關鍵傳記細節。
Studies of ancient rocks suggest that fragments of solid crust existed as far back as 4bn years ago, when the Earth was mostly covered in water, but their genesis remains disputed.
對古代巖石的研究表明，固體地殼的碎片早在40億年前就已經存在了，當時地球大部分被水覆蓋，但它們的起源仍然存在爭議。
While plate tectonics are the dominant mechanism for generating new continental crust today, in the distant past Earth’s subsurface temperatures are widely thought to have been too hot to allow plates to form.
雖然板塊構造是今天形成新的大陸地殼的主要機制，但在遙遠的過去，人們普遍認為地球的地下溫度太高，不能形成板塊。
A paper published this week in Nature attempts to resolve this conundrum.
本周發表在《自然》雜志上的一篇論文試圖解決這個難題。
Tim Johnson of Curtin University, Australia, and his colleagues argue that the planet’s transformation was not triggered by forces from within, but from outer space—in the form of collisions from meteorites that disrupted the surface, causing fragments of the crust to melt in the presence of water, cool and resolve themselves into buoyant patches of land that would later act as nuclei for new continents.
澳大利亞科廷大學的蒂姆·約翰遜和他的同事們認為，地球的轉變不是由內部的力量引發的，而是來自外部空間的--隕石碰撞破壞了地球表面，導致地殼碎片在水的存在下融化，冷卻并分解成漂浮的小塊陸地，這些陸地后來成為新大陸的核心。
Dr Johnson’s thesis is not new, but the lack of direct evidence means it has never taken root.
約翰遜博士的論點并不新鮮，但缺乏直接證據，這也意味著這個論點從未站穩腳跟。
The more popular explanation for the first continent formation points the finger at plumes of hot matter rising from the Earth’s mantle to the surface, much like bubbles in a lava lamp.
對于第一個大陸形成，更流行的解釋是熱物質從地幔上升到地表，很像熔巖燈中的氣泡。
Then, if sufficiently hot, their underside would melt to produce buoyant granite, leading to the first continental plateaus.
然后，如果溫度足夠高，它們的底部會融化，產生漂浮的花崗巖，形成第一個大陸高原。
The new study offers evidence that sits uncomfortably with this theory.
這項新研究提供了與這一理論不符的證據。
Dr Johnson and his colleagues looked at the Pilbara craton, an approximately 3.5bn-year-old slab of north-western Australia, roughly the size of Germany, which represents one of the few remaining scraps of the early Earth’s continental crust.
約翰遜博士和他的同事們研究了皮爾巴拉地區的古陸核，這是澳大利亞西北部的一個大約有35億年歷史的板塊，大致相當于德國的大小，是早期地球大陸地殼為數不多的殘余之一。
