The Pangaea Pop-up - Michael Molina

大陸的形成 - 麥克．莫利納

譯者: woo liu 審譯者: Dong Mao

Once upon a time,

從前

South America lived harmoniously alongside Africa

南美洲就在於非洲旁邊

until a crack in the Earth

直到地球的一個裂縫

drove the two continents apart.

將兩大洲分離

This breakup began about 200 million years ago

這一裂縫始於2億年前

during the separation of the supercontinent

超級大陸分離期

known as Pangaea.

這個超級大陸也叫盤古大陸

Their proximity back then

當初兩大洲的相連

explains why the same plant fossils and reptile fossils,

可以解釋為何某些相同植物化石和

like the Mesosaurus,

諸如中龍類的爬行類動物的化石

can be found on the South American east coast

同時分佈在南美洲的東岸

and African west coast.

和非洲的西岸

However, this evidence does not account

然而 這項證據並不能

for how the continents moved apart.

顯示兩大洲的分裂方式

For that, we'll need to take a close look

因此 我們必須對我們腳底下的大陸

at the earth below our feet.

來個更仔細的觀察

Though you may not realize it,

你或許還不知道

the ground below you is traveling across the Earth

你腳底下的陸地

正以每年10公分的速度 相當於你指甲生長的速度

at a rate of about 10 cm/year,

在地球表面移動

or the speed at which your fingernails grow.

This is due to plate tectonics,

這些移動是因為板塊的構造

or the large-scale movement of Earth's continents.

或是地球各大洲劇烈的移動所造成的

The motion occurs within the top two layers

這些移動發生於

of the Earth's mantle,

地幔的最上兩層：

the lithosphere and asthenosphere.

岩石圈和軟流圈

The lithosphere,

岩石圈

which includes the crust and uppermost mantle,

包含了地殼和地涵的上層

comprises the land around you.

並構成了你周遭的陸地

Beneath the lithosphere

岩石圈底下

is the asthenosphere

便是軟流圈

the highly viscous but solid rock portion

軟流圈具有高度的黏性

of the upper mantle.

亦是上部地幔的堅硬部分

It's between 80 and 200 km

他的深度位於

below the Earth's surface.

地球表面80至200公里之間

While the asthenosphere wraps around the Earth's core

軟流圈以整圈不中斷的形式

as one connected region,

包覆於地核的外圍

the lithosphere is separated on top

然而 岩石圈

into tectonic plates.

卻在上方分開成一塊塊的板塊

There are seven primary tectonic plates

我們現在所知道的地球

that compose the shape of the planet we know today.

是由七塊主要的板塊所構成

Like the other smaller tectonic plates,

這些主要板塊的厚和其他較小的板塊一樣

the primary plates are about 100 km thick

約莫是100公里厚

and are composed of one or two layers:

而這些板塊是由大陸地殼或海洋地殼

continental crust and oceanic crust.

以單層或雙層的形式建構出來的

Continental crust forms the continents

大陸地殼形成了各大洲

and areas of shallow water close to their shores,

以及岸邊的淺水地帶

whereas oceanic crust forms the ocean basins.

而海洋地殼則構成了海洋盆地

The transition from the granitic continental crust

花崗岩質的大陸地殼和

to the basaltic oceanic crust

玄武岩質的海洋地殼的分界線

occurs beyond the continentel shelf,

位於大陸棚的後方

in which the shore suddenly slopes down

在大陸棚的後方

towards the ocean floor.

海岸急速下降到海底

The South American Plate is an example

南美洲板塊便是一例

of a tectonic plate made of two crusts:

由兩個地殼組成的板塊

the continent we know from today's map

其中一個是我們所知道的南美洲

and a large region of the Atlantic Ocean around it.

另一個則是周圍一部份的大西洋

Collectively comprising the lithosphere,

這些板塊包含了岩石圈

these plates are brittler and stiffer

且相較於下方可塑性強的軟流圈

than the heated, malleable layer of the asthenosphere below.

更為堅硬和脆弱

Because of this,

因此

the tectonic plates float on top of this layer,

這些板塊比差分開的

independently of one another.

漂浮在軟流圈之上

The speed and direction in which these tectonic plates move

這些板塊

depends on the temperature and pressure

根據下方軟流圈的不同壓力和溫度

of the asthenosphere below.

而有不同的移動方向和移動速率

Scientists are still trying to nail down

科學家仍企圖找出

the driving forces behind this movement,

促使這些運動發生的作用力

with some theories pointing towards mantle convection,

有些理論將矛頭指向地幔對流

while others are examining

而有些則是繼續觀察

the influence of the Earth's rotation

地球的轉動和引力

and gravitational pull.

是否為這些作用力的源頭

Though the mechanics have not been sorted out,

雖然當中的機械理論部分 尚未被分析出來

the scientific community agrees

但是科學界仍一致同意

that our tectonic plates are moving

我們所身處的板塊

and have been for billions of years.

已經流動了幾十億年了

Because these plates move independently,

由於這些板塊是獨自的運動

a fair amount of pushing and pulling

因此極為龐大的交互作用

between the plates occurs.

便發生於這些板塊之間

The first type of interaction

第一種交互作用力

is a divergent boundary,

是使相鄰兩板塊相離的斥力

in which two plates move away from one another.

是使相鄰兩板塊相離的斥力

We see this in the Mid-Atlantic Ridge

我們在南美洲和非洲之間的

between South America and Africa.

大西洋中脊便可看見此現象

The next interaction is when two plates collide,

下一個交互作用力 發生於兩板塊碰撞時

known as a convergent boundary.

又被稱為是聚合力

In this instance, the land is pushed upward

在這撞擊的一瞬間

to form large mountain ranges,

陸地被往上推擠並形成山脈

like the Himalayas.

而喜馬拉雅山便是一例

In fact, the Indian Plate is still colliding

其實 印度板塊現仍正與歐亞板塊

with the Eurasian Plate,

發生擠壓

which is why Mount Everest

這也是為什麼珠穆朗瑪

grows one cm/year.

以每年1公分的速率生長著

Finally, there's the transform boundaries,

最後則是兩板塊

where two plates scrape past one another.

平行擦過的剪力

The grinding of the transform boundary

剪力的摩擦作用

leads to many earthquakes,

造成很多的地震

which is what happens

而聖安地列斯斷層

in the 810 mile-long San Andreas Fault.

便是一例

The moving Earth is unstoppable,

地球的移動是不會停止的

and, while a shift of 10 cm/year may not seem like a lot,

雖然每年10公分的 些微變化看似不是很多

over millions of years our planet will continue

但是幾百萬年後的地球

to dramatically change.

仍會有著巨大的改變

Mountains will rise,

山脈會一個個隆起

shorelines will recede,

海岸線會倒退

islands will pop up.

島嶼一個個出現

In fact, one projected map shows

事實上 一個虛擬地圖顯示

the cities of Los Angeles and San Francisco

洛杉磯和舊金山

on top of each other.

相疊在一起的樣貌

Maybe South America and Africa

或許南美洲和非洲

will come together again, too.

有天又會合併為一塊

Only time will tell.

惟有時間能驗證