新视野大学英语读写教程听力 第三册 te-unit06-b

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[00:00.00]喜欢hxen.net，就把hxen.net复制到QQ个人资料中！Changes in the Balance of Nature
[00:-1.00]1  Perceptions are relative.
[00:-2.00]2  A single tree may seem large compared to a person.
[00:-3.00]If you compare it to a mountain,however,
[00:-4.00]the large tree seems small.
[00:-5.00]In other words, things in nature are large or small,
[00:-6.00]new or old, only in accordance with the measures
[00:-7.00]and the comparisons involved.
[00:-8.00]3  During the duration of one human lifetime,
[00:-9.00]not many things change. Even trees live longer than people,
[00:10.00]and the Earth itself is far older.
[00:11.00]The Earth was formed about five billion years ago from a rotating,
[00:12.00]circular cloud of dust and gases such as hydrogen and nitrogen.
[00:13.00]A billion years later, the planet had cooled,
[00:14.00]and the continents and the great bodies of water had formed.
[00:15.00]4  About 3.5 billion years ago, another great change occurred.
[00:16.00]The oceans began to develop an enormous system of living things,
[00:17.00]with many diverse forms of life,
[00:18.00]all dependent on one another.
[00:19.00]The first animals on this living sphere, the Earth,
[00:20.00]were primitive marine animals,
[00:21.00]and then around 500 million years ago these sea animals developed shells.
[00:22.00]Seventy million years later, the first fish appeared.
[00:23.00]Next, insects developed, about 400 million years ago.
[00:24.00]After another 200 million years,
[00:25.00]dinosaurs and the first mammals walked the Earth.
[00:26.00]About 200 million years ago,
[00:27.00]warm-blooded animals took to the air — the first birds.
[00:28.00]Fifty million years later,
[00:29.00]both birds and mammals were well established.
[00:30.00]About three million years ago, scientists believe,
[00:31.00]the first human beings walked the Earth.
[00:32.00]Life was now flourishing.
[00:33.00]5  In terms of the evolution of life on Earth,
[00:34.00]human beings have just arrived.
[00:35.00]Despite their short time on Earth, however,
[00:36.00]people have brought about enormous changes to the surface of the planet
[00:37.00]— changes far out of proportion to the interval of time
[00:38.00]they have occupied it.
[00:39.00]6  People Try to Control Resources
[00:40.00]7  People have more control over their surroundings
[00:41.00]than any other species on Earth.
[00:42.00]With the combination of intelligence and manual skill
[00:43.00](allowing us to make and use tools),
[00:44.00]people have found ways to use plant and animal resources,
[00:45.00]mineral ores, fuels, and many other of Earth's materials and resources.
[00:46.00]8  As the number of people on Earth increases,
[00:47.00]it becomes increasingly difficult for the population to survive
[00:48.00]on the resources of the land.
[00:49.00]The amount of land is limited.
[00:50.00]Although agricultural production can be increased
[00:51.00]by use of machinery such as tractors and the addition of fertilizer,
[00:52.00]the land ultimately can produce only so much food and no more.
[00:53.00]As the human population grows, people consume more.
[00:54.00]Clearly, some locations on Earth already have too many people;
[00:55.00]in many of these areas,
[00:56.00]future increases will surely bring about more poverty and suffering.
[00:57.00]Yet people in rich nations use proportionally
[00:58.00]far more of the available resources than people in poorer nations.
[00:59.00]As they consume these resources without restraint,
[-1:00.00]they also waste large amounts of them.
[-1:-1.00]9  People are only a very small fraction
[-1:-2.00]of all the living things on the planet.
[-1:-3.00]Yet their numbers create a drain on resources that can't be renewed.
[-1:-4.00]For example, the amount of water on Earth is limited;
[-1:-5.00]this water is cleaned through natural processes.
[-1:-6.00]However, the natural processes for filtering water
[-1:-7.00]can clean only a certain amount of water by removing the pollution.
[-1:-8.00]10  Likewise, a limited amount of petroleum