最新研究表明，古代地球可能是一個(gè)沒(méi)有大陸的“水世界”

最新研究表明，古代地球可能是一個(gè)沒(méi)有大陸的“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.

今天海洋覆蓋了地球表面超過(guò)70%的面積，但是在30億年前，整個(gè)地球可能都被水覆蓋著。

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.

為了調(diào)查數(shù)十億年前我們的星球是什么樣子，一組研究人員在澳大利亞內(nèi)陸皮爾巴拉克拉通的一個(gè)被稱為全景的地質(zhì)遺址上采用了間接的分析方法。今天，這個(gè)地區(qū)距離陸地100公里(62英里)，但是32億年前，它還在水下深處。事實(shí)上，那里曾經(jīng)有一個(gè)古老的熱液噴口，海水從海底冒泡而出。

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.

研究報(bào)告的第一作者、愛(ài)荷華州立大學(xué)的助理教授本杰明·約翰遜(Benjamin Johnson)在一份聲明中說(shuō):“周?chē)鷽](méi)有真正的古代海水樣本，但我們確實(shí)有巖石與海水發(fā)生了相互作用，并記住了這種相互作用。”

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.

研究人員收集了超過(guò)100個(gè)這樣的巖石樣本，并發(fā)現(xiàn)了其中的一些特別之處:氧的一種特殊同位素的含量略高一些。同位素是一種原子核中中子數(shù)不同的元素。地球上絕大多數(shù)的氧是氧-16，含有8個(gè)質(zhì)子和8個(gè)中子。然而，地球上約0.20%的氧由10個(gè)中子組成，被稱為氧-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.

來(lái)自澳大利亞的樣本表明，該地區(qū)古代的水比現(xiàn)在含有更多的氧-18。由于大陸上覆蓋著富含粘土的土壤，能夠有效地捕獲氧-18，研究小組認(rèn)為，如果沒(méi)有大陸上覆蓋著土壤，海洋中可能存在更多的氧-18。他們的發(fā)現(xiàn)確實(shí)表明，在32.4億年前，地球上并沒(méi)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."

“在我們所做的研究中，沒(méi)有任何東西說(shuō)不可能有微小的大陸從海洋中伸出來(lái)，”合著者Boswell Wing補(bǔ)充道，他是科羅拉多大學(xué)博爾德分校地質(zhì)科學(xué)系的副教授。“我們只是不認(rèn)為有像我們今天這樣的全球性大陸土壤形成。”

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.

研究人員不知道大陸何時(shí)以及如何開(kāi)始從海洋中出現(xiàn)，但他們計(jì)劃調(diào)查“更年輕”的巖層，以拼湊出更精確的時(shí)間軸。研究結(jié)果發(fā)表在《自然地球科學(xué)》雜志上。

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