Earth’s crust is getting thinner than ever, thanks to a rapidly cooling interior The thinnest it’s been in 170 million years. 地球的地殼是 1.7 億年來最薄的,這要感謝急速降溫的地心

[fusion_builder_container hundred_percent=”no” equal_height_columns=”no” menu_anchor=”” hide_on_mobile=”small-visibility,medium-visibility,large-visibility” class=”” id=”” background_color=”” background_image=”” background_position=”center center” background_repeat=”no-repeat” fade=”no” background_parallax=”none” parallax_speed=”0.3″ video_mp4=”” video_webm=”” video_ogv=”” video_url=”” video_aspect_ratio=”16:9″ video_loop=”yes” video_mute=”yes” overlay_color=”” video_preview_image=”” border_size=”” border_color=”” border_style=”solid” padding_top=”” padding_bottom=”” padding_left=”” padding_right=””][fusion_builder_row][fusion_builder_column type=”1_1″ type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” border_position=”all” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”small-visibility,medium-visibility,large-visibility” center_content=”no” last=”true” min_height=”” hover_type=”none” link=”” first=”true”][fusion_text]Earth’s crust is getting thinner than ever, thanks to a rapidly cooling interior
The thinnest it’s been in 170 million years.
地球的地殼是 1.7 億年來最薄的,這要感謝急速降溫的地心

If you looked back at Earth 170 million years ago, you’d find a very different planet. The world’s continents were all linked up into one vast ‘supercontinent’ called Pangaea, and according to a new study, the outermost layer of the planet was 1.7 km (1 mile) thicker than it is today.
Researchers have found that since the break-up of Pangaea, Earth’s inner mantle has been cooling twice as fast as we thought, and it looks like its crust has been thinning out ever since.

如果你回溯 1.7 億年前的地球,你會看到一顆很不一樣的星球。這個世界的大陸都連結到一個稱為盤古大陸( Pangaea )的「 超級大陸 」( supercontinent ),根據一個新研究,最外層的地層曾經比現在的要多厚上 1.7 公里( 1 英里 )。研究人員發現自從盤古大陸分裂,地球內部的地函的冷卻速度要比我們想像的快兩倍,而且地殼變得前所未有的薄。

“It’s important to note [that] Earth seems to be cooling a lot faster now than it has been over its lifetime,” says geophysicist Van Avendonk from the University of Texas.
“The current state of Earth, where we have a lot of plate tectonic events, this allows Earth to cool much more efficiently than it did in the past.”
To trace the changes in Earth’s outer layer over the past 2.5 billion years, they analysed 234 measurements of crust thickness from around the world over a number of geological ages.

德克薩斯州大學( University of Texas )的地球物理學家 Van Avendonk 說:「 這很重要,我們必須意識到地球冷卻的速度前所未有的快,比地球以往的任何時候都快。地球目前的狀態有許多板塊運動( plate tectonic ),這讓地球能比它以往更有效率地冷卻。」

為了追蹤地球在過去 25 億年的外部地層變化,他們分析了 234 個對世界各地不同地質年代的地殼厚度的測量。

They found that oceanic crust formed in the mid-Jurassic 170 million years ago was 1.7 km (1 mile) thicker than the crust that’s being produced today, and since then, the mantle below has been cooling much more rapidly than expected.

So why is Earth’s crust thinning out?
The outermost crust of Earth is formed by the mantle, which sits between the scorching hot core and the crust, spanning some 2,900 km (1,802 miles), and making up a whopping 84 percent of the planet’s total volume.

他們發現在中侏羅紀, 1.7 億年前形成的海洋地殼要比現在的厚上 1.7 公里( 1 英里 ),從那時起,地函的冷卻速度要比預期的快。所以,為什麼地球的地殼變薄了?地球最外層的地殼由地函構成,地函位在炙熱的地核和地殼間,橫跨約 2900 公里( 1802 英里 ),佔有整個星球總體積的百分之 84。

Magma produced in the mantle forms the outer oceanic crust when it rises to the surface and cools into rock.
Based on chemical analyses of lava rocks, Avendonk and his team found that since about 2.5 billion years ago, the mantle has been cooling at a rate of 6 to 11 degrees Celsius every 100 million years.
But then something happened around 170 million years ago to bump that cooling rate up to as much as 20 degrees per 100 million years ever since.

由地函製造的岩漿噴出地表,冷卻後成為岩石,組成了外部海洋地殼。根據熔岩的科學分析, Avendonk 和他的團隊發現自從 25 億年前以來,地函每一億年以攝氏 6 到 11 度的速度冷卻。但是在 1.7 億年以前發生了一些事,讓冷卻速度來到每一億年降溫攝氏 20 度。

“While scientists expected the mantle to cool over time as heat left over from Earth’s formation and from radioactive decay dissipates, this degree of cooling was surprising,” Thomas Sumner explains for Science News.
The researchers suspect that plate tectonics – the theory that Earth’s ‘outer shell’ is divided into several plates that glide over the mantle – could explain the cooling.
One of the biggest changes to Earth’s plates occurred from 200 to 170 million years ago, when Pangaea split apart and eventually formed the separated continents we know today, and it looks like this spread led to everything cooling down.
“What we think is happening is that the supercontinent was like an insulating blanket,” Van Avendonk explains in a press release.
“So when these continents started opening up and the deeper mantle was exposed, more or less, to the atmosphere and the ocean it started cooling much faster.”

Thomas Sumner 向科學新聞( Science News )解釋:「 雖然科學家本來就預測,當熱從地球的結構離開,以及從放射性衰變(Radioactive Decay)消散,地函會隨著時間冷卻,但是這種程度的冷卻令人很意外。」

研究人員認為板塊運動( 地球的外部地殼分為數塊,並且在地函上滑行的理論 )可以解釋這場冷卻。其中一個地球最大的板塊變化發生在 2 到 1.7 億年前,盤古大陸最終分裂並形成今日我們知道的分裂大陸,看來這個事件導致了冷卻。

Van Arendonk 在一份新聞稿中表示:「 我們的認為,超級大陸就像是一塊絕緣毯,當這些大陸分裂開,地函露出,或多或少,向大氣以及海洋暴露,於是它開始更快地冷卻。」

It’s thought that the way Earth’s tectonic plates sink, shift, and form during significant eras of change like the gradual break-up of Pangaea shifts heat in the planet’s interior, affecting how it cools in certain areas.
“While mantle temperatures below the Pacific Ocean have decreased around 13 degrees per 100 million years, the mantle below the Atlantic and Indian oceans has cooled about 37 degrees per 100 million years,” Sumner reports for Science News.
This difference appears to be linked to the oceans’ distance from the continents.

這個理論認為,地球的板塊在重要的時期下沉、偏移以及形變,就像盤古大陸逐漸的分裂使地球內部的熱變動,在一些特定區域影響了地球的冷卻。 Sumner 向科學新聞( Science News )說:「 雖然太平洋底下的地函溫度每一億年減少了大約攝氏 13 度,大西洋和印度洋底下的地函每一億年減少了約攝氏 37 度。」

這裡的差異與海洋和大陸的距離產生連結。

The study could not only explain why Earth’s crust appears to be getting thinner with age – it could also explain why Pangaea split up in the first place: all the heat below that giant ‘insulating blanket’ might have eventually broke through and split the landmass apart.
“This could explain why you get a breakup about 100 million years after you get a supercontinent assembled,” Laurent Montési, a geodynamicist at the University of Maryland in College Park, who wasn’t involved in the study, told Sumner.
The research has been published in Nature Geosciences.

這個研究不只解釋了為何地球的地殼漸漸變薄,它也解釋了為何盤古大陸當初會分裂。所有在那巨大「 絕緣毯 」下的熱,或許最後終將突破而出,撕裂大陸。

馬里蘭大學學院市分校( University of Maryland in College Park )的一位並沒有參與此研究的地球動力學家( geodynamicist ), Laurent Montési 向 Sumner 表示:「 這解釋了為何超級大陸( supercontinent )出現後約一億年會有一次分裂。」

這份研究被刊載在《自然-地質科學》( Nature Geoscience ) 期刊。

來源:sciencealert

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