Once upon a time, South America lived harmoniously alongside Africa until a crack in the Earth drove the two continents apart.
很久以前，南美洲和非洲紧邻着，直到地球上出现一道裂缝，把两个大陆分开。
This breakup began about 200 million years ago during the separation of the supercontinent known as Pangaea.
这次分裂发生在大约2亿年前，当时被称为泛大陆的超级大陆开始分裂。
Their proximity back then explains why the same plant fossils and reptile fossils, like the Mesosaurus,
两块大陆曾紧紧相邻，这解释了为什么相同的植物化石和爬行动物化石，比如中龙化石，
can be found on the South American east coast and African west coast.
会出现在南美东海岸和非洲西海岸。
However, this evidence does not account for how the continents moved apart.
然而, 这个证据无法解释大陆是如何分离的。
For that, we'll need to take a close look at the earth below our feet.
因此, 我们需要更加仔细地看看我们脚下的地球。
Though you may not realize it, the ground below you is traveling across the Earth at a rate of about 10 cm/year,
虽然你可能没有意识到，但你脚下的陆地正在地球上以大约每年十厘米的速度漂移，
or the speed at which your fingernails grow.
也就是你指甲生长的速度。
This is due to plate tectonics, or the large-scale movement of Earth's continents.
这是由于板块构造或大陆的大规模移动。
The motion occurs within the top two layers of the Earth's mantle, the lithosphere and asthenosphere.
这种运动发生在地幔的最上面两层中，也就是岩石圈和软流层。
The lithosphere, which includes the crust and uppermost mantle, comprises the land around you.
岩石圈包括地壳和上地幔顶部，也就是你脚下的陆地。
Beneath the lithosphere is the asthenosphere the highly viscous but solid rock portion of the upper mantle.
在岩石圈以下是软流层，它是上地幔中粘稠度高，但又为固态岩石的部分。
It's between 80 and 200 km below the Earth's surface.
它在地表以下80千米到200千米之间的地方。
While the asthenosphere wraps around the Earth's core as one connected region,
软流层包裹着地核，使之成为一个连续的整体，
the lithosphere is separated on top into tectonic plates.
最上方的岩石圈被分为不同的板块。
There are seven primary tectonic plates that compose the shape of the planet we know today.
如今我们知道，地球表面是由七个主要板块构成的。
Like the other smaller tectonic plates,
和其他小板块一样，
the primary plates are about 100 km thick and are composed of one or two layers: continental crust and oceanic crust.
主要板块大约有100公里厚，由一或两层地壳组成：陆壳和洋壳。
Continental crust forms the continents and areas of shallow water close to their shores,
陆壳构成陆地和靠近海岸的浅水地区，
whereas oceanic crust forms the ocean basins.
而洋壳形成洋盆。
The transition from the granitic continental crust to the basaltic oceanic crust occurs beyond the continentel shelf,
从花岗岩的陆壳到玄武岩质的洋壳的转变，发生在大陆架以外的地方，
in which the shore suddenly slopes down towards the ocean floor.
在那里，海岸骤然下降到洋底。
The South American Plate is an example of a tectonic plate made of two crusts:
南美洲板块就是这样一个由陆壳和洋壳构成板块的例子：
the continent we know from today's map and a large region of the Atlantic Ocean around it.
我们从如今的地图中知道, 它由南美洲大陆和周围大部分的大西洋地区组成。
Collectively comprising the lithosphere,
这些板块构成岩石圈，
these plates are brittler and stiffer than the heated, malleable layer of the asthenosphere below.
比下面高温、粘稠的软流层更脆、更硬。

Because of this, the tectonic plates float on top of this layer, independently of one another.
正因为如此，构造板块互相独立的浮在软流层上。
The speed and direction in which these tectonic plates move depends on the temperature and pressure of the asthenosphere below.
这些板块移动的速度和方向，取决于下方软流层的温度和压强。
Scientists are still trying to nail down the driving forces behind this movement,
科学家们仍在努力研究造成这一运动的驱动力是什么，
with some theories pointing towards mantle convection,
一些理论认为是地幔的对流，
while others are examining the influence of the Earth's rotation and gravitational pull.
而其他一些则认为是由于地球自转还有引力作用的影响。
Though the mechanics have not been sorted out,
虽然力学原因没有弄清，
the scientific community agrees that our tectonic plates are moving and have been for billions of years.
但科学界一致同意我们的构造板块正在移动，而且已经进行了数十亿年。
Because these plates move independently, a fair amount of pushing and pulling between the plates occurs.
因为这些板块各自移动，板块之间就会产生大量的推和拉的相互作用。
The first type of interaction is a divergent boundary, in which two plates move away from one another.
其中第一种相互作用是分离型板块边界，两个构造板块向相反方向背离运动。
We see this in the Mid-Atlantic Ridge between South America and Africa.
比如南美洲和非洲之间的大西洋洋中脊就是这样。
The next interaction is when two plates collide, known as a convergent boundary.
第二种相互作用类型是板块碰撞，被称为汇聚型板块边界。
In this instance, the land is pushed upward to form large mountain ranges, like the Himalayas.
在这个例子中, 陆地被抬升，形成大山脉，比如喜马拉雅山。
In fact, the Indian Plate is still colliding with the Eurasian Plate, which is why Mount Everest grows one cm/year.
事实上, 印度板块与欧亚板块至今仍在对撞，这就是为什么珠穆朗玛峰每年升高一厘米。
Finally, there's the transform boundaries, where two plates scrape past one another.
最后一种类型, 是转换型板块边界，两个板块在水平方向相对滑动。
The grinding of the transform boundary leads to many earthquakes,
这种转换型边界的摩擦造成了地震的频发，
which is what happens in the 810 mile-long San Andreas Fault.
这就是发生在810英里长的圣安德烈斯断层中的情况。
The moving Earth is unstoppable, and, while a shift of 10 cm/year may not seem like a lot,
地球的运动是不可阻挡的，虽然每年移动十厘米看起来不多，
over millions of years our planet will continue to dramatically change.
而我们星球数百万年来的持续运动将带来沧海桑田的变化。
Mountains will rise, shorelines will recede, islands will pop up.
山峦会上升，海岸线会消退，岛屿会露出海面。
In fact, one projected map shows the cities of Los Angeles and San Francisco on top of each other.
事实上, 一幅预期的地图显示，洛杉矶和旧金山两个城市彼此将十分靠近。
Maybe South America and Africa will come together again, too. Only time will tell.
也许南美洲和非洲还会再次走到一起。这只有时间能够证明。