我们知道到了19世纪90年代，从地球对太阳和月亮的引力的响应方式来看，这颗行星有一个致密的核心，可能是铁。 1906年，理查德·迪克森·奥尔德姆发现地震波穿过地球中心的速度远远低于它周围的地幔 – 因为中心是液体。 1936年Inge Lehmann报告说，有些东西反映了核心内部的地震波。很明显，核心由一层厚厚的液态铁组成 – 外部核心 – 中心有一个较小的实心内核。它很坚固，因为在那个深度，高压克服了高温的影响。 2002年，哈佛大学的Miaki Ishii和Adam Dziewonski发表了大约600公里的“最内层核心”的证据。 2008年夏松松和孙新蕾提出了一个不同的内核，内径约1200公里。在其他人确认工作之前，这些想法不多。无论我们学习什么，都会提出新的问题。液态铁必须是地球地磁场的来源 – 地球动力学 – 但它是如何工作的？为什么地质动力学会在地质时间内翻转，切换磁性北极和南极？在熔岩金属遇到岩石地幔的核心顶部会发生什么？答案在20世纪90年代开始出现。
新加坡共和理工学院Essay代写：关于地球的核心
We knew by the 1890s, from the way Earth responds to the gravity of the Sun and Moon, that the planet has a dense core, probably iron. In 1906 Richard Dixon Oldham found that earthquake waves move through the Earth’s center much slower than they do through the mantle around it—because the center is liquid. In 1936 Inge Lehmann reported that something reflects seismic waves from within the core. It became clear that the core consists of a thick shell of liquid iron—the outer core—with a smaller, solid inner core at its center. It’s solid because at that depth the high pressure overcomes the effect of high temperature. In 2002 Miaki Ishii and Adam Dziewonski of Harvard University published evidence of an “innermost inner core” some 600 kilometers across. In 2008 Xiadong Song and Xinlei Sun proposed a different inner inner core about 1200 km across. Not much can be made of these ideas until others confirm the work. Whatever we learn raises new questions. The liquid iron must be the source of Earth’s geomagnetic field—the geodynamo—but how does it work? Why does the geodynamo flip, switching magnetic north and south, over geologic time? What happens at the top of the core, where molten metal meets the rocky mantle? Answers began to emerge during the 1990s.