How North America got its shape - Peter J. Haproff

譯者: Helen Chang 審譯者: 伟秾 肖

The geography of our planet is in flux.

我們星球的地理環境不斷在變化。

Each continent has ricocheted around the globe on one or more tectonic plates,

每塊大陸都曾隨著一個 或多個板塊彈跳環球過，

changing quite dramatically with time.

相當顯著地與時俱變。

Today, we'll focus on North America

今天，我們將專注於「北美」

and how its familiar landscape and features

其熟悉的地貌和特色

emerged over hundreds of millions of years.

如何於數億年間成形。

Our story begins about 750 million years ago.

故事約始於七億五千萬年前。

As the super continent Rodinia becomes unstable,

超大陸「羅迪尼亞」變得不穩，

it rifts along what's now the west coast of North America

它沿著現今的北美西海岸位置

to create the Panthalassa Ocean.

形成「泛大洋」。

You're seeing an ancestral continent called Laurentia,

你見到的是被稱為 「勞倫大陸」的古大陸，

which grows over the next few hundred million years

在接下來的數億年間體積增大，

as island chains collide with it and add land mass.

因被島嶼鏈撞擊而增加面積。

We're now at 400 million years ago.

時間來到四億年前。

Off today's east coast, the massive African plate inches westward,

在今天的東海岸外， 巨大的非洲板塊緩慢西移，

closing the ancient Iapetus Ocean.

合攏了古「巨神海」。

It finally collides with Laurentia at 250 million years

它終於在兩億五千萬年前 撞上了勞倫大陸，

to form another supercontinent Pangea.

形成另一個超級大陸： 「盤古大陸」。

The immense pressure causes faulting and folding,

巨大的壓力造成斷層和折疊，

stacking up rock to form the Appalachian Mountains.

疊高的岩石形成阿巴拉契亞山脈。

Let's fast forward a bit.

時間快轉前進一些些。

About 100 million years later, Pangea breaks apart,

約一億年後，盤古大陸裂開了，

opening the Southern Atlantic Ocean

打開「南大西洋」，

between the new North American Plate and the African Plate.

位於新成形的「北美​​板塊」 和「非洲板塊」之間。

We forge ahead,

時間加速前進，

and now the eastward-moving Farallon Plate

此時向東移動的「法拉龍板塊」

converges with the present-day west coast.

匯合現今的西海岸。

The Farallon Plate's greater density makes it sink beneath North America.

法拉龍板塊的密度較大， 因此沉到北美板塊之下。

This is called subduction,

這就是「隱沒」。

and it diffuses water into the magma-filled mantle.

水擴散到充滿岩漿的地函裡，

That lowers the magma's melting point

使得岩漿的熔點降低，

and makes it rise into the overlying North American plate.

並升入覆蓋其上的北美板塊。

From a subterranean chamber, the magma travels upwards

岩漿從地下的空間向上流動，

and erupts along a chain of volcanos.

沿著一長列的火山而爆發。

Magma still deep underground slowly cools,

還留在地底深處的岩漿逐漸冷卻，

crystallizing to form solid rock,

結晶成為堅硬的岩石，

including the granite now found in Yosemite National Park

包括常見於優勝美地國家公園 和內華達山脈的花崗岩。

and the Sierra Nevada Mountains.

We'll come back to that later.

我們稍後再談。

Now, it's 85 million years ago.

時間進到八千五百萬年前。

The Farallon Plate becomes less steep,

法拉龍板塊變得平緩，

causing volcanism to stretch eastward and eventually cease.

致使火山向東延伸，終於停了下來。

As the Farallon Plate subducts,

法拉龍板塊的隱沒

it compresses North America,

壓縮了北美，

thrusting up mountain ranges like the Rockies,

推高了山脈，像是 延伸三千英里的「洛磯山脈」。

which extend over 3,000 miles.

Soon after, the Eurasian Plate rifts from North America,

不久後，「歐亞板塊」 自北美板塊撕裂出來，

opening the North Atlantic Ocean.

打開「北大西洋」。

We'll fast forward again.

時間再次快速前進。

The Colorado Plateau now uplifts,

「科羅拉多​​高原」隆起，

likely due to a combination of upward mantle flow

起因可能來自地幔上升 和北美板塊增厚的共同作用。

and a thickened North American Plate.

In future millennia, the Colorado River will eventually sculpt the plateau

在接下來的幾千年中，

科羅拉多河切割高原

into the epic Grand Canyon.

成為史詩般的「大峽谷」。

30 million years ago, the majority of the Farallon Plate sinks into the mantle,

三千萬年前，絕大部分的 法拉龍板塊沉入地函，

leaving behind only small corners still subducting.

只留下繼續隱沒的小角落。

The Pacific and North American plates converge

「太平洋板塊」和北美板塊匯聚，

and a new boundary called the San Andreas Fault forms.

形成的新邊界被稱為 「聖安德烈亞斯斷層」。

Here, North America moves to the south,

在這裡，南移的北美板塊

sliding against the Pacific Plate, which shifts to the north.

摩擦北移的太平洋板塊。

This plate boundary still exists today,

此板塊的邊界今天仍存在，

and moves about 30 millimeters per year

每年約移動三公分，

capable of causing devastating earthquakes.

足以引起破壞性極大的地震。

The San Andreas also pulls apart western North America

聖安德烈亞斯還沿著 很寬的裂谷帶拉開北美西部。

across a wide rift zone.

This extensional region is called the Basin and Range Province,

這個延伸區域被稱為「盆嶺區」，

and through uplift and erosion,

透過抬升和侵蝕作用，

is responsible for exposing the once deep granite of Yosemite and the Sierra Nevada.

使原先深埋於優勝美地 和內華達山脈的花崗岩露了出來。

Another 15 million years off the clock,

又過了一千五百萬年，

and magma from the mantle burns a giant hole into western North America,

地函裡的岩漿 在北美西部燒穿出巨洞，

periodically erupting onto the surface.

週期性地噴出地表。

Today, this hotspot feeds an active supervolcano

如今，黃石國家公園底下的 超級活火山熱點，

beneath Yellowstone National Park.

It hasn't erupted in the last 174,000 years,

已經十七萬四千年未曾爆發過了。

but if it did,

但是，如果它一旦爆發，

its sheer force could blanket most of the continent with ash

其龐大的力量將會使得

黑灰覆蓋北美的大部分天空，

that would blacken the skies and threaten humanity.

並威脅人類。

The Yellowstone supervolcano is just one reminder

黃石的超級火山只是個提醒，

that the Earth continues to seethe below our feet.

地球持續在我們的腳下沸騰著。

Its mobile plates put the planet in a state of constant flux.

移動的板塊使得地球的狀態 不斷地變化。

In another few hundred million years,

誰知道再過幾億年後，

who knows how the landscape of North America will have changed.

北美的地景將變成什麼模樣。

As the continent slowly morphs into something unfamiliar,

隨著大陸慢慢地變形成陌生的樣貌，

only geological time will tell.

只有地質時間能說分明。