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Using point and examples from the lecture, explain two ways weathering occurs.
请用课上的观点和例子，解释说明风化发生的两种途径。
Listen to part of a lecture in a geology class.
请听地理课上的部分内容。
Rocks near the Earth's surface are directly exposed to elements in the environment such as air and water,
靠近地表的岩石直接暴露在像空气和水这样的环境元素中，
and also to conditions such as temperature change as well as to living organisms.
也会受到像温度变化和生物体这样的情况的影响。
And this exposure to the environment can actually cause even huge rocks to break into smaller pieces.
像这样暴露在自然环境中，实际上可能会导致巨大的岩石碎成小块儿。
This process is called weathering.
这个过程就叫做“风化”。
Let's talk about a couple ways weathering occurs.
我们来讲一讲风化发生的几种途径。
First of all, rocks are often exposed to water.
首先，岩石经常会接触到水。
In cold wet environments rocks can break due to water freezing inside of them.
在寒冷潮湿的环境中，岩石可能会因为内部的水分冻结而破裂。
How does this happen? Well, as I am sure you know, when water freezes it expands and over time this can lead to weathering.
这是如何发生的呢？我相信你们都知道，当水结冰的时候，它的体积会膨胀，而随着时间的推移，这就可能会导致风化。
Um, imagine a rock with a small opening or crack in it. It rains and water gets into the crack and stays there.
假设有这么一块岩石，它的表面有个小缺口或者裂缝。下雨的时候，雨水落进了裂缝里并留了下来。
Then, at night, the temperature drops and the water inside the crack freezes.
然后到了晚上气温下降，裂缝里的雨水结成了冰。
This growing, expanding ice pushes outward on either side of the crack causing it to get slightly bigger.
这块越来越大的冰从裂缝的两边不断往外伸展，把裂缝变得稍微大了一些。
When this happens again and again, the crack becomes larger and eventually pieces of the rock break off.
如果这种情况反复发生，裂缝会变得越来越大，最终部分岩石就会脱落。
OK, weathering can also be caused by plants, by a plant growth.
风化也会因为植物而产生，受到植物生长的影响。
If a plant seed gets blown into the crack of a rock, it may take roots. And its roots will grow down into the rock.
当一粒植物种子被风吹进岩石的裂缝之后，它也许会在此生根。而它的根会一直往下生长穿进岩石。
The plant's roots can cause the rock to break down, uh, fracture.
植物的根会导致岩石破裂。
You may have seen this with large trees growing on top of a rock, a great example of this.
你们也许见过大树长在岩石上面，这就是个绝佳的例子，
Usually there's enough dirt in the crack of a rock or on top of a rock to allow a tree to start growing there.
一般来说，岩石的裂缝里或者岩石上方有充足的泥土可以让一棵树开始在那儿生长。
As the tree grows over the years, the tree's roots extend downward into the crack and crevasses of the rock in search of water and nutrients.
当这棵树长了几年之后，它的根就会向下延伸进裂缝和岩石的缺口中，寻找水分和营养。
Over time, the roots get bigger and grow deeper, widening and enlarging the cracks, causing the rock to break apart.
随着时间的推移，树根会越长越大、越长越深，不断使裂缝变宽变大，导致岩石破裂。
