Earth Systems and Resources
AP Environmental Science Topic 4 7:28 English narration · English + 中文 subtitles burned in
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Two towns, forty kilometres apart, on opposite sides of one mountain range.
两个小镇相距四十公里，分别位于同一条山脉的两侧。
One of them gets three metres of rain a year — a rainforest.
其中一个每年降雨三米——是雨林。
The other gets less than a tenth of that — a desert.
另一个还不到它的十分之一——是沙漠。
Same latitude. Same ocean nearby.
纬度相同，离海也一样近。
What makes the difference?
是什么造成了差别？
The answer is in this topic.
答案就在这个专题里。
Unit Four is Earth's systems: the moving crust under our feet, the soil it makes, the air above it, the winds that circle the planet, and the water that runs off it.
第四单元讲的是地球的各个系统：脚下移动的地壳、它造出的土壤、 上方的空气、环绕行星的风，以及从陆地流走的水。
Let's start at the bottom.
我们从最底下开始。
Plate tectonics: Earth's crust is broken into plates that drift slowly on the hot mantle below.
地球的地壳被分成许多板块，在下方炽热的地幔上缓慢漂移。
What happens at their edges depends on which way they move.
边缘发生什么，取决于它们的运动方向。
At a divergent boundary the plates pull apart, and molten rock rises to make new crust.
在离散边界，板块彼此拉开， 熔融的岩石上升，形成新的地壳。
At a convergent boundary they collide, building mountains, volcanoes and earthquakes.
在汇聚边界，它们相撞，造出山脉、火山和地震。
At a transform boundary they simply slide past each other — no new crust and no volcano, but plenty of earthquakes.
在转换边界，它们只是彼此错动——没有新地壳，没有火山，但地震很多。
How slow is slow?
到底有多慢？
A plate moves five centimetres a year — about the speed your fingernails grow.
一个板块每年移动五厘米——大约和指甲生长的速度一样。
Now give it geological time.
现在给它地质时间。
Multiply five centimetres by one million years. That comes to five million centimetres, which is fifty kilometres.
用五厘米乘以一百万年，得到五百万厘米，也就是五十公里。
A movement you cannot even see, repeated for a million years, opens oceans and builds mountain ranges.
一个你根本看不见的移动，重复一百万年，就能张开大洋、造出山脉。
Those mountains eventually become soil.
那些山脉最终会变成土壤。
Soil starts as rock that weathers — broken down by water, ice and living things.
土壤始于岩石的风化——被水、冰和生物分解。
Dead plants and animals add organic matter on top.
死去的动植物在上面增添有机质。
Over hundreds or thousands of years this settles into layers we call horizons: dark organic topsoil, then paler mineral layers, then broken rock.
经过数百甚至数千年，这些逐渐沉积成一层层， 我们称为土层：深色的有机表土，然后是较浅的矿质层，再往下是碎裂的岩石。
Erosion is the removal of that soil by wind and water, and we speed it up whenever we strip the plants off.
侵蚀是风和水把这些土壤带走，而每当我们把植被剥去，就会加快它。
Soil forms slowly, so erosion faster than formation means the soil is simply gone.
土壤形成很慢，所以如果侵蚀快过形成，土壤就彻底没了。
Now soil composition and properties.
土壤到底由什么组成？
What is it actually made of? Sand, silt and clay, plus organic matter, water and air.
沙、粉砂和黏土，再加上有机质、水和空气。
Soil texture is the mix of those three mineral sizes — sand is coarse, silt is medium, clay is fine.
土壤质地就是这三种矿物颗粒大小的配比——沙最粗，粉砂居中，黏土最细。
Texture decides two properties the exam loves.
质地决定了考试最爱考的两个性质。
Porosity is how much space there is between the grains, so how much water the soil can hold.
孔隙度是颗粒之间有多少空隙，也就是土壤能储存多少水。
Permeability is how easily water moves through it.
渗透性是水穿过它的难易程度。
Sand drains fast but holds nothing.
沙排水快，但什么也留不住。
Clay holds water but drains badly.
黏土能保水，但排水很差。
Loam, a balance of all three, is the best soil for plants.
壤土是三者的平衡，是最适合植物的土壤。
Now look up.
现在往上看。
The atmosphere is layered.
大气是分层的。
The troposphere is the bottom layer — where we live, and where all the weather happens.
对流层是最底下的一层——我们生活在这里， 所有的天气也发生在这里。
The stratosphere sits above it, and it holds the ozone layer that blocks ultraviolet light.
平流层在它上面，其中的臭氧层能阻挡紫外线。
Above those come the mesosphere and the thermosphere.
再往上是中间层和热层。
As for what the air is made of: seventy-eight percent nitrogen, twenty-one percent oxygen, and about one percent everything else.
至于空气的成分：百分之七十八是氮，百分之二十一是氧， 其余大约百分之一是别的气体。
That one percent includes the greenhouse gases — a tiny share of the air that controls the planet's temperature.
这百分之一里包括温室气体—— 占空气极小的一部分，却控制着地球的温度。
Sunlight does not hit the Earth evenly, and that drives the winds.
阳光照到地球上并不均匀，这驱动了风。
At the equator the sun is strongest, so the air heats, rises, and dumps its rain — which is why the rainforests sit there.
在赤道，太阳最强，空气受热上升， 把水汽变成雨降下——所以雨林长在那里。
That air travels toward the poles, cools, and sinks at about thirty degrees, bone dry — which is why the great deserts sit there.
这些空气向两极移动、冷却， 在大约三十度处下沉，此时已极为干燥——所以大沙漠都在那里。
Those are the global wind patterns, and they make three convection cells in each hemisphere: Hadley, Ferrel and polar.
这样每个半球形成三个环流圈：哈得来环流、费雷尔环流和极地环流。
And because the Earth spins, every one of these winds is bent sideways. That is the Coriolis effect.
而由于地球自转，这些风全都被偏转——这就是科里奥利效应。
Water that falls on the land has to go somewhere.
落在陆地上的水总要去某个地方。
A watershed is all the land that drains into one common body of water — a river, a lake, or the sea.
流域是指所有汇入同一个水体的陆地—— 一条河、一个湖或大海。
The ridge line between two watersheds is called the divide: rain landing on one side goes one way, rain on the other side goes the other.
两个流域之间的山脊线叫分水岭： 落在一侧的雨往一边流，落在另一侧的往另一边流。
Watersheds matter because everything that happens on that land ends up in that water.
流域之所以重要，是因为那片土地上发生的一切最终都会进入那片水里。
Fertiliser from a farm, oil from a road, soil from a bare field — it all drains downhill together.
农田的化肥、马路上的机油、裸露田地里的泥土——全都顺坡一起流下去。
Now solar radiation and Earth's seasons.
为什么会有季节？
Why do we have them? Earth's axis is tilted by about twenty-three point five degrees, and it keeps pointing the same way all year.
地球的自转轴倾斜约二十三点五度，而且一整年都指向同一个方向。
So as Earth orbits the Sun, the hemisphere tilted toward the Sun gets more direct sunlight and longer days — that is its summer.
所以当地球绕太阳公转时，朝向太阳倾斜的那个半球得到更直射的阳光和更长的白昼—— 那就是它的夏天。
Six months later that hemisphere is tilted away, and that is its winter.
六个月后，那个半球背向太阳，那就是冬天。
Note the cause: the tilt, and not because Earth is closer to the Sun.
注意原因：是倾斜，而不是因为地球离太阳更近。
The distance barely changes.
距离几乎没有变化。
The same tilt is why the tropics stay warm all year and the poles stay cold.
同样的倾斜也让热带全年温暖，两极长年寒冷。
Earth's geography and climate: four things about a place decide it.
一个地方的气候由四件事决定。
Latitude sets the angle of the sunlight: straight down at the equator, slanted at the poles.
纬度决定阳光的入射角：在赤道垂直照下，在两极则很斜。
Elevation cools things down — go up a mountain and the temperature falls, roughly six degrees for every thousand metres.
海拔会降温——爬上山，气温就下降，大约每上升一千米下降六度。
The ocean moderates temperature, because water heats and cools far more slowly than land, so coastal places have milder summers and milder winters.
海洋能调节温度，因为水的升温和降温都比陆地慢得多， 所以沿海地区夏天和冬天都更温和。
And the fourth is mountains — which brings us back to our two towns.
第四个是山脉——这就把我们带回那两个小镇。
Here is the answer.
答案就在这里。
Wet air blows in from the ocean and meets a mountain range. It has nowhere to go but up.
潮湿的空气从海洋吹来，遇到一条山脉，除了向上别无去路。
As the air rises it cools, the water vapour condenses, and it rains — hard — on the windward side. That is our rainforest town.
空气上升时冷却，水汽凝结，于是在迎风坡下起大雨——那就是我们的雨林小镇。
By the time the air comes down the other side it has already lost its water, and sinking air warms and dries out.
等空气从另一侧下来时，水分已经丢光，而下沉的空气会增温变干。
That leeward side is the rain shadow, and that is our desert town.
背风的那一侧就是雨影区，那就是我们的沙漠小镇。
Same latitude, same ocean, one mountain in between.
同样的纬度，同样的海洋，中间只隔着一座山。
One last system, and it changes weather worldwide.
最后一个系统，它能改变全球的天气。
Normally the trade winds push warm surface water west across the Pacific, and cold, nutrient-rich water rises along South America, feeding a huge fishery. In an El Niño year those winds weaken. The warm pool slides back east, the cold upwelling is capped, and the fishery collapses.
正常情况下，信风把温暖的表层水向西推过太平洋， 而寒冷、富含养分的水在南美沿岸上涌，养育了一个巨大的渔场。
Rainfall moves with the warm water, so some regions flood while others go into drought.
在厄尔尼诺年，这些风减弱。 暖水团滑回东边，冷水上涌被压住，渔场随之崩溃。
La Niña is the opposite: stronger winds, and an unusually cold eastern Pacific.
降雨随暖水移动，于是有些地区洪水，另一些地区干旱。
El Nino and La Nina together are the biggest year-to-year swing in the system.
拉尼娜正好相反：信风更强，东太平洋异常寒冷。
Three ways to keep your marks.
三个保住分数的方法。
First, seasons come from the tilt of Earth's axis, not from the distance to the Sun — write that and you keep the mark.
第一，季节来自地轴的倾斜，而不是与太阳的距离—— 写清这一点就能拿分。
Second, soil forms slowly, so when erosion beats formation the loss is permanent.
第二，土壤形成很慢，所以当侵蚀快过形成时，损失是永久的。
Third, explain the global winds from two things: uneven heating, and the Coriolis effect from the spinning Earth.
第三，解释全球风带要说两点：受热不均，以及地球自转带来的科里奥利效应。
Get those right, and Unit Four is yours.
做对这些，第四单元就是你的了。