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The geography of our planet is in flux.
我们星球的地理环境不断在变化。
Each continent has ricocheted around the globe on one or more tectonic plates, changing quite dramatically with time.
每块大陆都曾随着一个或多个板块弹跳环球过，相当显著地与时俱变。
Today, we'll focus on North America and how its familiar landscape and features emerged over hundreds of millions of years.
今天，我们将专注于北美洲的熟悉的地貌和特色如何于数亿年间成形。
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,
超大陆罗迪尼亚变得不稳，
it rifts along what's now the west coast of North America to create the Panthalassa Ocean.
它沿着现今的北美西海岸位置形成泛大洋。
You're seeing an ancestral continent called Laurentia,
你见到的是被称为劳伦大陆的古大陆，
which grows over the next few hundred million years as island chains collide with it and add land mass.
在接下来的数亿年间体积增大，因被岛屿链撞击而增加面积。
We're now at 400 million years ago.
时间来到四亿年前。
Off today's east coast, the massive African plate inches westward, closing the ancient Iapetus Ocean.
在今天的东海岸外，巨大的非洲板块缓慢西移，合拢了古巨神海。
It finally collides with Laurentia at 250 million years to form another supercontinent Pangea.
它终于在两亿五千万年前撞上了劳伦大陆，形成另一个超级大陆：盘古大陆。
The immense pressure causes faulting and folding, stacking up rock to form the Appalachian Mountains.
巨大的压力造成断层和折迭，迭高的岩石形成阿巴拉契亚山脉。
Let's fast forward a bit.
时间快进一些。
About 100 million years later, Pangea breaks apart,
约一亿年后，盘古大陆裂开了，
opening the Southern Atlantic Ocean between the new North American Plate and the African Plate.
打开南大西洋，位于新成形的北美板块和非洲板块之间。
We forge ahead, and now the eastward-moving Farallon Plate converges with the present-day west coast.
时间加速前进，此时向东移动的法拉龙板块汇合现今的西海岸。
The Farallon Plate's greater density makes it sink beneath North America.
法拉龙板块的密度较大，因此沉到北美板块之下。
This is called subduction, and it diffuses water into the magma-filled mantle.
这就是隐没。水扩散到充满岩浆的地函里。
That lowers the magma's melting point and makes it rise into the overlying North American plate.
使得岩浆的熔点降低，并升入覆盖其上的北美板块。
From a subterranean chamber, the magma travels upwards and erupts along a chain of volcanos.
岩浆从地下的空间向上流动，沿着一长列的火山而爆发。
Magma still deep underground slowly cools, crystallizing to form solid rock,
还留在地底深处的岩浆逐渐冷却，结晶成为坚硬的岩石，
including the granite now found in Yosemite National Park and the Sierra Nevada Mountains.
包括常见于约塞米蒂国家公园和内华达山脉的花岗岩。
We'll come back to that later. Now, it's 85 million years ago.
我们稍后再谈。时间进到八千五百万年前。
The Farallon Plate becomes less steep, causing volcanism to stretch eastward and eventually cease.
法拉龙板块变得平缓，致使火山向东延伸，终于停了下来。
As the Farallon Plate subducts, it compresses North America,
法拉龙板块的隐没压缩了北美，
thrusting up mountain ranges like the Rockies, which extend over 3,000 miles.
推高了山脉，像是延伸三千英里的落基山脉。
Soon after, the Eurasian Plate rifts from North America, opening the North Atlantic Ocean.
不久后，欧亚板块自北美板块撕裂出来，打开北大西洋。
We'll fast forward again.
时间再次快速前进。
The Colorado Plateau now uplifts, likely due to a combination of upward mantle flow and a thickened North American Plate.
科罗拉多高原隆起，起因可能来自地幔上升和北美板块增厚的共同作用。
In future millennia, the Colorado River will eventually sculpt the plateau into the epic Grand Canyon.
在接下来的几千年中，科罗拉多河切割高原，成为史诗般的大峡谷。
30 million years ago, the majority of the Farallon Plate sinks into the mantle,
三千万年前，绝大部分的法拉龙板块沉入地函，
leaving behind only small corners still subducting.
只留下继续隐没的小角落。
The Pacific and North American plates converge and a new boundary called the San Andreas Fault forms.
太平洋板块和北美板块汇聚，形成的新边界被称为圣安德烈亚斯断层。
Here, North America moves to the south, sliding against the Pacific Plate, which shifts to the north.
在这里，南移的北美板块摩擦北移的太平洋板块。
This plate boundary still exists today,
此板块的边界今天仍存在，
and moves about 30 millimeters per year capable of causing devastating earthquakes.
每年约移动三公分，足以引起破坏性极大的地震。
The San Andreas also pulls apart western North America across a wide rift zone.
圣安德烈亚斯还沿着很宽的裂谷带拉开北美西部。
This extensional region is called the Basin and Range Province, and through uplift and erosion,
这个延伸区域被称为盆岭区，通过抬升和侵蚀作用，使
is responsible for exposing the once deep granite of Yosemite and the Sierra Nevada.
原先深埋于优胜美地和内华达山脉的花岗岩露了出来。
Another 15 million years off the clock,
又过了一千五百万年，
and magma from the mantle burns a giant hole into western North America, periodically erupting onto the surface.
地函里的岩浆在北美西部烧穿出巨洞，周期性地喷出地表。
Today, this hotspot feeds an active supervolcano beneath Yellowstone National Park.
如今，这个热点为黄石国家公园下面的一座活跃的超级火山提供了养料。
It hasn't erupted in the last 174,000 years, but if it did,
它已经十七万四千年未曾爆发过了，但是如果它一旦爆发，
its sheer force could blanket most of the continent with ash that would blacken the skies and threaten humanity.
其庞大的力量将会使得黑灰覆盖北美的大部分天空，并威胁人类。
The Yellowstone supervolcano is just one reminder that the Earth continues to seethe below our feet.
黄石的超级火山只是个提醒，地球持续在我们的脚下沸腾着。
Its mobile plates put the planet in a state of constant flux.
移动的板块使得地球的状态不断地变化。
In another few hundred million years, who knows how the landscape of North America will have changed.
谁知道再过几亿年后，北美的景观将变成什么模样。
As the continent slowly morphs into something unfamiliar, only geological time will tell.
随着大陆慢慢地变形成陌生的样貌，只有地质时间能说清。
