大陆形成新学说，教科书要改了？(上)

Science & technology

科技版块

Forming continents

形成大陆

Impact creator

撞击的创造者

Earth may have been shaped by forces from outer space

地球可能是由外太空的力量塑造的

The earth is a poor archivist.

地球是一个糟糕的档案保管员。

The rigid tectonic plates of its outer layers are continuously in motion, sliding over one another to swallow almost all records of the past, melting them into the mantle and then casting them anew.

刚性板块不断运动，相互滑动，吞噬了几乎所有过去的记录，将它们熔化到地幔中，然后重新浇铸。

This makes it difficult to reconstruct the 4.5bn-year-old planet’s formative years.

这使得很难重建这颗有45亿年历史的行星的形成期。

A particular problem is the crucial biographical detail of how the first continents came to be.

一个特别的问题是关于第一个大陆是如何形成的关键传记细节。

Studies of ancient rocks suggest that fragments of solid crust existed as far back as 4bn years ago, when the Earth was mostly covered in water, but their genesis remains disputed.

对古代岩石的研究表明，固体地壳的碎片早在40亿年前就已经存在了，当时地球大部分被水覆盖，但它们的起源仍然存在争议。

While plate tectonics are the dominant mechanism for generating new continental crust today, in the distant past Earth’s subsurface temperatures are widely thought to have been too hot to allow plates to form.

虽然板块构造是今天形成新的大陆地壳的主要机制，但在遥远的过去，人们普遍认为地球的地下温度太高，不能形成板块。

A paper published this week in Nature attempts to resolve this conundrum.

本周发表在《自然》杂志上的一篇论文试图解决这个难题。

Tim Johnson of Curtin University, Australia, and his colleagues argue that the planet’s transformation was not triggered by forces from within, but from outer space—in the form of collisions from meteorites that disrupted the surface, causing fragments of the crust to melt in the presence of water, cool and resolve themselves into buoyant patches of land that would later act as nuclei for new continents.

澳大利亚科廷大学的蒂姆·约翰逊和他的同事们认为，地球的转变不是由内部的力量引发的，而是来自外部空间的--陨石碰撞破坏了地球表面，导致地壳碎片在水的存在下融化，冷却并分解成漂浮的小块陆地，这些陆地后来成为新大陆的核心。

Dr Johnson’s thesis is not new, but the lack of direct evidence means it has never taken root.

约翰逊博士的论点并不新鲜，但缺乏直接证据，这也意味着这个论点从未站稳脚跟。

The more popular explanation for the first continent formation points the finger at plumes of hot matter rising from the Earth’s mantle to the surface, much like bubbles in a lava lamp.

对于第一个大陆形成，更流行的解释是热物质从地幔上升到地表，很像熔岩灯中的气泡。

Then, if sufficiently hot, their underside would melt to produce buoyant granite, leading to the first continental plateaus.

然后，如果温度足够高，它们的底部会融化，产生漂浮的花岗岩，形成第一个大陆高原。

The new study offers evidence that sits uncomfortably with this theory.

这项新研究提供了与这一理论不符的证据。

Dr Johnson and his colleagues looked at the Pilbara craton, an approximately 3.5bn-year-old slab of north-western Australia, roughly the size of Germany, which represents one of the few remaining scraps of the early Earth’s continental crust.

约翰逊博士和他的同事们研究了皮尔巴拉地区的古陆核，这是澳大利亚西北部的一个大约有35亿年历史的板块，大致相当于德国的大小，是早期地球大陆地壳为数不多的残余之一。