Tang Ming, Chen Hao, Lee Cin-Ty A, Cao Wenrong
Key Laboratory of Orogenic Belt and Crustal Evolution, MOE, School of Earth and Space Sciences, Peking University, Beijing 100871, China.
Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA.
Sci Adv. 2024 Sep 13;10(37):eadq1952. doi: 10.1126/sciadv.adq1952. Epub 2024 Sep 11.
Earth owes much of its dynamic surface to its bimodal hypsometry, manifested by high-riding continents and low-riding ocean basins. The thickness of the crust in the lithosphere exerts the dominant control on the long-wavelength elevations of continents. However, there is a limit to how high elevations can rise by crustal thickening. With continuous crustal thickening, the mafic lower crust eventually undergoes a densifying phase transition, arresting further elevation gain-an effect clearly observed in modern orogenic belts. On early Earth, lower crust densification should also limit how high a thickening crust can rise, regardless of the thickening mechanisms. We suggest that lower crust densification combined with a thicker oceanic crust in the Archean may have limited the whole-Earth topographic relief to 3 to 5 kilometers at most-half that of the present day. Unless the oceans were far less voluminous, limited relief would inevitably lead to a water world on early Earth.
地球充满活力的表面很大程度上归功于其双峰式高度分布，表现为高耸的大陆和低洼的海洋盆地。岩石圈中地壳的厚度对大陆的长波长海拔高度起着主导控制作用。然而，地壳增厚能使海拔升高到何种程度是有限度的。随着地壳持续增厚，镁铁质下地壳最终会经历致密化相变，从而阻止海拔进一步升高——这种效应在现代造山带中清晰可见。在早期地球，无论增厚机制如何，下地壳致密化也应限制增厚地壳能够升高的高度。我们认为，太古宙下地壳致密化与更厚的洋壳相结合，可能已将全球地形起伏限制在至多3至5千米——仅为现今的一半。除非当时的海洋体积远小于现在，否则有限的地形起伏将不可避免地导致早期地球成为一个水世界。
