Perceptions are relative. A single tree may seem large compared to a person. If you compare it to a mountain, however, the large tree seems small. In other words, things in nature are large or small, new or old, only in accordance with the measures and the comparisons involved. 
During the duration of one human lifetime, not many things change. Even trees live longer than people, and the Earth itself is far older. The Earth was formed about five billion years ago from a rotating, circular cloud of dust and gases such as hydrogen and nitrogen. A billion years later, the planet had cooled, and the continents and the great bodies of water had formed. About 3.5 billion years ago, another great change occurred. The oceans began to develop an enormous system of living things, with many diverse forms of life, all dependent on one another. The first animals on this living sphere, the Earth, were primitive marine animals, and then around 500 million years ago these sea animals developed shells. Seventy million years later, the first fish appeared. Next, insects developed, about 400 million years ago. After another 200 million years, dinosaurs and the first mammals walked the Earth. About 200 million years ago, warm-blooded animals took to the air — the first birds. Fifty million years later, both birds and mammals were well established. About three million years ago, scientists believe, the first human beings walked the Earth. Life was now flourishing. In terms of the evolution of life on Earth, human beings have just arrived. Despite their short time on Earth, however, people have brought about enormous changes to the surface of the planet — changes far out of proportion to the interval of time they have occupied it. People Try to Control Resources People have more control over their surroundings than any other species on Earth. With the combination of intelligence and manual skill (allowing us to make and use tools), people have found ways to use plant and animal resources, mineral ores, fuels, and many other of Earth's materials and resources. As the number of people on Earth increases, it becomes increasingly difficult for the population to survive on the resources of the land. The amount of land is limited. Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer, the land ultimately can produce only so much food and no more. As the human population grows, people consume more. Clearly, some locations on Earth already have too many people; in many of these areas, future increases will surely bring about more poverty and suffering. Yet people in rich nations use proportionally far more of the available resources than people in poorer nations. As they consume these resources without restraint, they also waste large amounts of them. People are only a very small fraction of all the living things on the planet. Yet their numbers create a drain on resources that can't be renewed. For example, the amount of water on Earth is limited; this water is cleaned through natural processes. However, the natural processes for filtering water can clean only a certain amount of water by removing the pollution. Likewise, a limited amount of petroleum can be found under the Earth's surface. Petroleum is a valuable resource. Should people use it up to manufacture petrol for automobiles? As people work to control the planet and make life comfortable, are they using up resources that are needed for their survival? The Balance of Nature 
All natural systems tend toward balance among opposing factors or forces. Human activities can cause or accelerate permanent changes in natural systems. The smoke of one small fire causes no harm to the environment. Natural cleaning processes can clean the particles of smoke from the air. However, the collective smoke from thousands of factories, over the past two centuries, has caused enormous increases in air pollution levels worldwide. Cleaning this smoke has exceeded the protective ability of natural processes. The forests cannot clean the air fast enough. In spite of rapid population increase and industrial growth, some groups of people, often in remote areas, have been able to live in harmony with the planet. These people have not changed their ways of living from the ways of their ancestors. Called native peoples, they retain the ways of life that have remained unchanged for many generations. Many of their cultural values and ways of life include practices that return resources to the Earth. Human population growth is creating food shortages, problems of air quality, and changes in weather patterns. What is destroying rain forests and ruining the land and seas? What causes the acid rain that forms from water passing through polluted air? Why is there the threat of global warming? All these harmful results come from the too much use of resources and the human struggle to control the environment. The twentieth century began with powerful countries competing to take advantage of the Earth. As an outcome of their hunger for empires, the Earth was abused. Now people all over the world are living with the problems caused by this abuse. Now that they are no longer ignorant of the causes of the sickness of our planet, they seek ways to help the Earth, to give back what they take away. Previously, mankind only used the Earth. Now everyone must protect planet Earth, a planet in danger.
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