How North America got its shape - Peter J. Haproff

翻译人员: Marini Qian 校对人员: Gabriella Hu

The geography of our planet is in flux.

地球的地理在变动。

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

每一个大洲在地球上的不同板块上移动，

changing quite dramatically with time.

随着时间有很大的变化。

Today, we'll focus on North America

今天，我们来讲讲

and how its familiar landscape and features

北美州现在的风景是如何通过

emerged over hundreds of millions of years.

亿万年形成的。

Our story begins about 750 million years ago.

我们的故事开始在7.5亿年之前。

As the super continent Rodinia becomes unstable,

超级大陆罗迪尼亚变得越来越不稳定，

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

它沿着北美的西海岸裂缝，

to create the Panthalassa Ocean.

形成了泛大洋海洋。

You're seeing an ancestral continent called Laurentia,

这是劳伦大陆。

which grows over the next few hundred million years

岛链与它碰撞，在接下来的几亿年里

as island chains collide with it and add land mass.

一直增加它的面积。

We're now at 400 million years ago.

4亿年前，

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

在今天北美的东岸，非洲板块向西移动，

closing the ancient Iapetus Ocean.

把古老的巨神海关起来了。

It finally collides with Laurentia at 250 million years

2.5亿年前，它终于与劳伦碰撞，

to form another supercontinent Pangea.

形成了另一个超级大陆，盘古。

The immense pressure causes faulting and folding,

巨大的压力导致断层和折叠，

stacking up rock to form the Appalachian Mountains.

让石头形成了阿巴拉契亚山脉。

Let's fast forward a bit.

让我们跳到一亿年前。

About 100 million years later, Pangea breaks apart,

盘古裂开时

opening the Southern Atlantic Ocean

在新的北美盘和非洲盘之间

between the new North American Plate and the African Plate.

开通了南大西洋。

We forge ahead,

再往前，

and now the eastward-moving Farallon Plate

向东移动的法拉龙板块

converges with the present-day west coast.

与今天的西海岸融合。

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

法拉龙板块更稠密，并且沉到北美底下。

This is called subduction,

这叫俯冲。

and it diffuses water into the magma-filled mantle.

俯冲把水扩散到充满岩浆的地幔，

That lowers the magma's melting point

降低了岩浆的熔点，

and makes it rise into the overlying North American plate.

导致板块升到顶上的北美板块。

From a subterranean chamber, the magma travels upwards

岩浆从一个地下室往上移动，

and erupts along a chain of volcanos.

从一串火山中爆发。

Magma still deep underground slowly cools,

还在地下的岩浆慢慢冷却，

crystallizing to form solid rock,

结晶成岩石，

including the granite now found in Yosemite National Park

比如说优胜美地和内华达山脉

and the Sierra Nevada Mountains.

的花岗岩。

We'll come back to that later.

我们等会儿再来谈这个。

Now, it's 85 million years ago.

8500万年前，

法拉龙板块变得没有那么陡，

The Farallon Plate becomes less steep,

causing volcanism to stretch eastward and eventually cease.

导致火山向东伸展，逐渐停下来。

法拉龙板块在俯冲的同时在压缩北美

As the Farallon Plate subducts,

it compresses North America,

thrusting up mountain ranges like the Rockies,

造成山脉，比如落基山脉，

which extend over 3,000 miles.

延伸大于3000英里。

Soon after, the Eurasian Plate rifts from North America,

不久之后，欧亚板块跟北美裂开了，

opening the North Atlantic Ocean.

打开北大西洋。

We'll fast forward again.

我们再往后看。

The Colorado Plateau now uplifts,

科罗拉多高原隆起，

likely due to a combination of upward mantle flow

多半是由于向上的地幔流

and a thickened North American Plate.

与更厚的北美板块。

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

在未来的一千年中，

科罗拉多河会将高原塑造成大峡谷。

into the epic Grand Canyon.

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

3千万年前，大部分法拉龙板块沉进地幔，

leaving behind only small corners still subducting.

只剩下小角落在俯冲。

The Pacific and North American plates converge

太平洋板块与北美板块汇集，

and a new boundary called the San Andreas Fault forms.

形成新的边界，圣安德烈亚斯断层。

Here, North America moves to the south,

在这里，北美州向南移动，

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

滑在太平洋板块旁边。

太平洋板块向北移动。

This plate boundary still exists today,

这个板块边界今天仍然存在，

and moves about 30 millimeters per year

每年移动30毫米，

capable of causing devastating earthquakes.

能够引起强烈的地震。

The San Andreas also pulls apart western North America

圣安地列斯也在很宽的裂谷带

across a wide rift zone.

拉开北美州。

This extensional region is called the Basin and Range Province,

这种外延区域叫做盆地和山脉省。

and through uplift and erosion,

通过隆起和侵蚀，

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

暴漏了以前

埋在优胜美地和内华达深处的花岗岩。

Another 15 million years off the clock,

1500万年后，

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

地幔的岩浆在西边的北美州烧一个大洞，

periodically erupting onto the surface.

定期喷发到表面。

Today, this hotspot feeds an active supervolcano

现在，这个热点养着一个超级活火山，

beneath Yellowstone National Park.

就在黄石公园地下。

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

它174,000年都没有爆发了，

but if it did,

但是如果它真爆发了，

its sheer force could blanket most of the continent with ash

它的力量可以把大部分北美州覆盖在灰尘里，

that would blacken the skies and threaten humanity.

把天色变黑，并且对人类有很大的危险。

The Yellowstone supervolcano is just one reminder

黄石的超级火山是在提醒我们

that the Earth continues to seethe below our feet.

地球在我们脚底下一直在沸腾。

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

地球的板块导致它不断变化。

In another few hundred million years,

数亿年后，

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

谁也不知道北美州的景观会有什么变化。

As the continent slowly morphs into something unfamiliar,

只有时间可以透露

only geological time will tell.

以后的北美州会什么样。