An early call for plate tectonics The composition of continental crust far back in Earth's history gives us insight into when plate tectonics ramped up and has influenced ocean chemistry. Greber et al. looked at titanium isotopes in shales, which form from eroded continental crustal sediments, to estimate the composition 3.5 billion years ago, closer to the origins of Earth. They found a silica-rich composition, which indicates that plate tectonics was happening deep in our distant past. Other changes in crustal composition might be linked to changing ocean chemistry and major events such as the oxygenation of our atmosphere. Science, this issue p. 1271 Titanium isotopes in shale rock require the occurrence of plate tectonics on Earth 3.5 billion years ago. Earth exhibits a dichotomy in elevation and chemical composition between the continents and ocean floor. Reconstructing when this dichotomy arose is important for understanding when plate tectonics started and how the supply of nutrients to the oceans changed through time. We measured the titanium isotopic composition of shales to constrain the chemical composition of the continental crust exposed to weathering and found that shales of all ages have a uniform isotopic composition. This can only be explained if the emerged crust was predominantly felsic (silica-rich) since 3.5 billion years ago, requiring an early initiation of plate tectonics. We also observed a change in the abundance of biologically important nutrients phosphorus and nickel across the Archean-Proterozoic boundary, which might have helped trigger the rise in atmospheric oxygen.

中文翻译：

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35亿年前长英质地壳和板块构造的钛同位素证据

对板块构造的早期呼吁 远在地球历史上的大陆地壳的组成使我们能够深入了解板块构造何时出现并影响了海洋化学。格雷伯等人。研究了由侵蚀的大陆地壳沉积物形成的页岩中的钛同位素，以估计 35 亿年前的成分，更接近地球的起源。他们发现了一种富含二氧化硅的成分，这表明板块构造发生在我们遥远的过去深处。地壳成分的其他变化可能与海洋化学变化和大气氧化等重大事件有关。科学，这个问题 p。1271 页岩中的钛同位素需要 35 亿年前地球上板块构造的发生。地球在大陆和洋底之间的海拔和化学成分方面表现出二分法。在这种二分法出现时进行重建对于理解板块构造何时开始以及海洋养分供应如何随时间变化很重要。我们测量了页岩的钛同位素组成以限制暴露于风化作用的大陆地壳的化学成分，发现所有时代的页岩都具有统一的同位素组成。这只能解释为自 35 亿年前以来出现的地壳主要是长英质（富含二氧化硅），需要板块构造的早期开始。我们还观察到太古宙-元古代边界具有重要生物学意义的营养物质磷和镍的丰度发生了变化，这可能有助于引发大气中氧气的增加。