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The team traversed the craton to collect zircon crystals, a mineral with two properties ideally suited to the task.
研究小組穿越古陸核采集鋯石晶體，這種礦物有兩種特性，非常適合這項任務。
First, their content of radioactive uranium decays to lead at a rate that can be used to calculate their age.
首先，他們的放射性鈾含量衰減成鉛的速度可以用來計算他們的年齡。
And second, the isotopes of oxygen found within their structure are representative of the environment in which they grew.
其次，在它們的結構中發現的氧同位素代表了它們生長的環境。
Zircons whose ratio of oxygen-18 to oxygen-16 is 0.5% higher than found in seawater, for example, would have originated far below Earth’s surface.
例如，在海水中發現的氧-18和氧-16的比率比高0.5%的鋯石可能起源于地球表面以下很遠的地方。
Those with values closer to those found in seawater formed much nearer the crust.
那些與海水中發現的值更接近的物質形成于更接近地殼的地方。
Analysis led the researchers to conclude that the oldest crystals on the Pilbara -- those formed around 3.5bn years ago -- must have originated close to the surface.
通過分析，研究人員得出結論，皮爾巴拉上最古老的晶體--大約形成于35億年前--一定起源于靠近地表的地方。
This favours impact formation, as zircons transported by mantle plumes would have more profound origins.
這有利于撞擊的形成，因為地幔熱柱搬運的鋯石具有更深的起源。
“Giant impacts plus water is a really good way of making a continent,” says Dr Johnson.
約翰遜博士說：“巨型撞擊加上水是形成大陸的一種非常好的方式?！?/p>
The textbooks will not be rewritten overnight.
教科書不會在一夜之間改寫。
Marion Garcon, a geologist at Clermont-Auvergne University in France, finds the evidence of impact formation plausible on a local scale, but says more evidence will be needed to extrapolate it planet-wide.
法國克萊蒙特-奧弗涅大學的地質學家馬里恩·加爾孔認為，在局部范圍內，撞擊形成的證據是可信的，但他表示，需要更多證據才能在全球范圍內推斷這一點。
Fortunately, this can be done.
幸運的是，這是可以做到的。
Ancient continental fragments exist in other parts of Australia as well as Canada and South Africa.
古老的大陸碎片存在于澳大利亞其他地區、加拿大和南非。
Analyses of their constituent zircons could well provide valuable supporting evidence that Earth’s continents owe their existence to bodies from outer space.
對其構成的鋯石的分析很好地提供有價值的佐證，證明地球大陸的存在應歸功于來自外太空的天體。
But the authors will also need to explain why zircons previously found at other, even older, sites do not display the same telltale signature of impact.
但作者還需要解釋，為什么之前在其他更古老的地點發現的鋯石沒有顯示出相同的撞擊跡象。
This work could be significant in other ways.
這項工作可能在其他方面具有重要意義。
While the rate of asteroid collisions experienced by early Earth generally declined over time, it may have spiked some 3.9bn years ago during a postulated event known as the Late Heavy Bombardment (lhb).
雖然早期地球經歷的小行星碰撞的概率通常會隨著時間的推移而下降，但在大約39億年前的一次假定事件-晚期重轟擊(LHB)期間，小行星碰撞的概率可能達到了峰值。
What are taken by some as signs of the lhb pockmark the static surfaces of Mars and the Moon.
一些人認為LHB的跡象在火星和月球的靜態表面上留下了凹坑。
Earth’s constant ructions, however, will have destroyed any signs of it.
然而，地球持續不斷的騷動將摧毀它的任何跡象。
If Dr Johnson is right, then the formation of the continents could be the first earthly evidence of one of the solar system’s most dramatic moments.
如果約翰遜博士是正確的，那么大陸的形成可能是太陽系最戲劇性時刻之一的第一個地球證據。
