Department of Earth Sciences, University of Oregon, Eugene, OR, USA.
Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
Nature. 2018 May;557(7706):545-548. doi: 10.1038/s41586-018-0131-1. Epub 2018 May 23.
The history of the growth of continental crust is uncertain, and several different models that involve a gradual, decelerating, or stepwise process have been proposed. Even more uncertain is the timing and the secular trend of the emergence of most landmasses above the sea (subaerial landmasses), with estimates ranging from about one billion to three billion years ago. The area of emerged crust influences global climate feedbacks and the supply of nutrients to the oceans , and therefore connects Earth's crustal evolution to surface environmental conditions. Here we use the triple-oxygen-isotope composition of shales from all continents, spanning 3.7 billion years, to provide constraints on the emergence of continents over time. Our measurements show a stepwise total decrease of 0.08 per mille in the average triple-oxygen-isotope value of shales across the Archaean-Proterozoic boundary. We suggest that our data are best explained by a shift in the nature of water-rock interactions, from near-coastal in the Archaean era to predominantly continental in the Proterozoic, accompanied by a decrease in average surface temperatures. We propose that this shift may have coincided with the onset of a modern hydrological cycle owing to the rapid emergence of continental crust with near-modern average elevation and aerial extent roughly 2.5 billion years ago.
大陆地壳生长的历史并不确定，已经提出了几种不同的模型，涉及逐渐的、减速的或阶段性的过程。更不确定的是大多数陆地（陆上陆地）出现在海平面以上的时间和长期趋势，估计范围从大约 10 亿年前到 30 亿年前。出露地壳的面积影响着全球气候反馈和向海洋输送营养物质的过程，因此将地球的地壳演化与地表环境条件联系起来。在这里，我们使用跨越 37 亿年的所有大陆页岩的三重氧同位素组成来限制随时间推移大陆的出现。我们的测量结果表明，在太古宙-元古宙边界处，页岩的平均三重氧同位素值呈阶段性总下降 0.08 个千分位。我们认为，我们的数据最好通过水岩相互作用性质的转变来解释，从太古代的近海岸转变为元古代的主要是大陆性的，同时平均表面温度下降。我们提出，这种转变可能与现代水循环的开始相吻合，因为大约 25 亿年前，大陆地壳的快速出现具有接近现代的平均海拔和航空范围。
