[论文解读] Protoplanetary Earth Formation: Further Evidence and Geophysical Implications

J. Marvin Herndon|arXiv (Cornell University)|Aug 29, 2004

Astro and Planetary Science参考文献 21被引用 8

一句话总结

本文提出地球形成于一颗类似木星的原行星内部，其 rocky 核心被压缩至当前半径的约64%，这解释了连续大陆地壳的形成，并在气态包层消散后引发地球膨胀。膨胀主要通过裂缝形成和地幔体积膨胀导致的玄武质填充实现，而非板块构造，重新解释洋中脊过程为重力蠕变而非对流驱动的扩张。

ABSTRACT

Recently, I showed that the "standard model" of solar system formation is wrong,yielding the contradiction of terrestrial planets having insufficiently massive cores, and showed instead the consistency of Eucken's 1944 concept of planets raining out in the central regions of hot, gaseous protoplanets. Planets generally consist of concentric shells of matter, but there has been no adequate geophysical explanation to account for the Earth's non-contiguous crustal continental rock layer, except by assuming that the Earth in the distant past was smaller and subsequently expanded. Here, I show that formation of Earth, from within a Jupiter-like protoplanet, will account for the compression of the rocky Earth to about 64 percent of its current radius, yielding a closed, contiguous continental shell with concomitant Earth expansion commencing upon the subsequent removal of its protoplanetary gaseous shell. I now propose that Earth expansion progresses, not from spreading at mid-oceanic ridges as usually assumed, but primarily by the formation of expansion cracks (often near continental margins) and the in-filling of those cracks with basalt (produced from volume expansion in the mantle), which is extruded mainly at mid-oceanic ridges, solidifies and traverses the ocean floor by gravitational creep to regions of lower gravitational potential energy, ultimately plunging downward into distant expansion cracks, emulating subduction. Viewed from that perspective, most of the evidence presented in support of plate tectonics supports Earth expansion; mantle convection is not required, and the timescale for Earth expansion is no longer constrained to about 200 million years, the maximum age of the current ocean floor.

研究动机与目标

• 解决标准太阳系模型中类地行星缺乏足够大质量核心的矛盾。
• 为地球连续大陆地壳提供地球物理学解释，挑战过去行星膨胀的假设。
• 将地球膨胀重新定义为原行星压缩和随后气态壳层移除的结果，而非构造扩张。
• 将洋中脊过程重新解释为喷出玄武岩的重力蠕变，而非地幔对流驱动的板块构造。
• 证明地球膨胀并不受制于洋壳最老约2亿年的时间尺度。

提出的方法

• 提出地球起源于一个致密的岩石核心，位于一个炽热的气态原行星内部，类似于木星。
• 模拟原行星阶段由于内部高压导致岩石核心被压缩至当前半径的约64%。
• 建议气态包层的移除触发膨胀，从大陆边缘的裂缝形成开始。
• 将新洋壳的形成归因于地幔体积膨胀，产生玄武岩并喷出，通过重力蠕变流向势能更低的区域。
• 将俯冲带重新解释为喷出的玄武岩流入远处的扩张裂缝，而非实际板块运动。
• 拒绝地幔对流作为膨胀驱动力，主张裂缝形成和玄武质填充为主要机制。

实验结果

研究问题

• RQ1 如何在不假设过去行星膨胀的前提下解释地球连续大陆地壳？
• RQ2 何种地球物理学机制可解释地球岩石核心被压缩至当前半径约64%的现象？
• RQ3 洋中脊过程能否通过喷出玄武岩的重力蠕变而非地幔对流和板块构造来解释？
• RQ4 若地球膨胀不受限于最老洋壳约2亿年的时间尺度，其时间尺度为何？
• RQ5 原行星形成模型如何解决标准太阳系形成模型中的核心质量矛盾？

主要发现

• 地球的岩石核心在形成于类似木星的原行星内部期间被压缩至当前半径的约64%，从而形成连续的大陆地壳。
• 原行星气态包层的移除引发地球膨胀，从大陆边缘的裂缝形成开始。
• 玄武质地壳通过地幔体积膨胀形成，喷出至洋中脊，并通过重力蠕变在洋底流动至重力势能更低的区域。
• 类似俯冲的特征被重新解释为玄武岩流入远处的扩张裂缝，而非板块汇聚或下沉。
• 地幔对流并非驱动膨胀所必需，且该过程不受限于洋壳约2亿年的时间尺度。
• 该模型调和了观测到的地球物理特征与非对流、膨胀驱动的机制，挑战了标准板块构造范式。