最新研究表明，古代地球可能是一个没有大陆的“水世界”

最新研究表明，古代地球可能是一个没有大陆的“水世界”

The ocean covers more than 70 percent of the surface of Earth today, but over 3 billion years ago the entire planet may have been covered in water.

今天海洋覆盖了地球表面超过70%的面积，但是在30亿年前，整个地球可能都被水覆盖着。

To investigate what our planet was like billions of years ago, a team of researchers turned to indirect methods of analysis at a geological site in the Australian Outback known as Panorama in the Pilbara Craton. Today, the region is 100 kilometers (62 miles) inland, but 3.2 billion years ago, it was deep underwater. In fact, there were also once ancient hydrothermal vents there where seawater bubbled up through the ocean floor.

为了调查数十亿年前我们的星球是什么样子，一组研究人员在澳大利亚内陆皮尔巴拉克拉通的一个被称为全景的地质遗址上采用了间接的分析方法。今天，这个地区距离陆地100公里(62英里)，但是32亿年前，它还在水下深处。事实上，那里曾经有一个古老的热液喷口，海水从海底冒泡而出。

Alfredo Carpineti

"There are no samples of really ancient ocean water lying around, but we do have rocks that interacted with that seawater and remembered that interaction," lead author Benjamin Johnson, an assistant professor at Iowa State University, said in a statement.

研究报告的第一作者、爱荷华州立大学的助理教授本杰明·约翰逊(Benjamin Johnson)在一份声明中说:“周围没有真正的古代海水样本，但我们确实有岩石与海水发生了相互作用，并记住了这种相互作用。”

The researchers collected over 100 of these rock samples and found something peculiar in them: a slightly higher amount of a particular isotope of oxygen. An isotope is a version of an element that has a different number of neutrons in its nucleus. The vast majority of oxygen on Earth is Oxygen-16 and contains eight protons and eight neutrons. However, about 0.20 percent of the planet’s oxygen consists of 10 neutrons and is known as Oxygen-18.

研究人员收集了超过100个这样的岩石样本，并发现了其中的一些特别之处:氧的一种特殊同位素的含量略高一些。同位素是一种原子核中中子数不同的元素。地球上绝大多数的氧是氧-16，含有8个质子和8个中子。然而，地球上约0.20%的氧由10个中子组成，被称为氧-18。

Benjamin Johnson inspects an outcrop in the Panorama district by what was once an ancient hydrothermal vent. Credit: Jana Meixnerova

Samples from Australia show that the region’s ancient water contained more Oxygen-18 than present times. Since continents are covered in clay-rich soil that is efficient at trapping Oxygen-18, the team suggests that without continents covered in soil, more Oxygen-18 would have been present in the ocean. Their discovery indeed suggests there wasn't much dry land available 3.24 billion years ago.

来自澳大利亚的样本表明，该地区古代的水比现在含有更多的氧-18。由于大陆上覆盖着富含粘土的土壤，能够有效地捕获氧-18，研究小组认为，如果没有大陆上覆盖着土壤，海洋中可能存在更多的氧-18。他们的发现确实表明，在32.4亿年前，地球上并没有多少旱地。

"There's nothing in what we've done that says you can't have teeny, micro-continents sticking out of the oceans," added co-author Boswell Wing, an associate professor in the Department of Geological Sciences at the University of Colorado Boulder. "We just don't think that there were global-scale formation of continental soils like we have today."

“在我们所做的研究中，没有任何东西说不可能有微小的大陆从海洋中伸出来，”合著者Boswell Wing补充道，他是科罗拉多大学博尔德分校地质科学系的副教授。“我们只是不认为有像我们今天这样的全球性大陆土壤形成。”

The researchers don’t know when and how continents began to emerge out of the ocean but they plan to investigate “younger” rock formations to piece together a more precise timeline. The findings are reported in Nature Geoscience.

研究人员不知道大陆何时以及如何开始从海洋中出现，但他们计划调查“更年轻”的岩层，以拼凑出更精确的时间轴。研究结果发表在《自然地球科学》杂志上。

This pillow basalt lined the seafloor roughly 3.2 billion years ago. Credit: Benjamin Johnson