The air animals and plants use to live is only the first level of the air around the Earth (the troposphere). The day to day changes in this level of air are named weather; the changes between places far away from each other and from year to year are named the climate. Rain and storms are both in this level. Both come about because this part of the air gets colder as it goes up. Cold air becomes thicker and falls, and warm air becomes thinner and goes up. The turning Earth moves the air as well and air moves north and south because the middle of the Earth generally gets more power from the Sun and is warmer than the north and south points. At the same time, air over water (specially very warm water) gets water in it but, because cold air is not able to take in as much water, it starts to make clouds and rain as it gets colder. The way water moves around in a circle like this is called the water cycle.
Above this first level, there are four other levels. The air gets colder as it goes up in the first level; in the second level (the stratosphere), the air gets warmer as it goes up. This level has a special kind of oxygen called ozone. The ozone in this air keeps living things safe from damaging rays from the Sun. The power from these rays is what makes this level warmer and warmer. The middle level (the mesosphere) gets colder and colder with height; the fourth level (the thermosphere) gets warmer and warmer; and the last level (the exosphere) is almost outer space and has very little air at all. It reaches about half the way to the Moon. The three outer levels have a lot of electric power moving through them; this is called the ionosphere and is important for radio and other electric waves in the air. It is also where the Northern Lights are.
Even though air seems very light, the weight of all of the air above the outside of the Earth (air pressure) is important. Generally, from sea level to the top of the outer level of the air, a space of air one cm across has a mass of about 1.03 kg and a space of air one sq in across has a weight of about 14.7 lb. The mass of the air also keeps the Earth safe when rocks (meteorites) hit it from outer space. Without the air, the damage meteorites do would be much greater. Because of the air, meteorites generally burn up long before they get to the earth.
The air also keeps the Earth warm, specially the half turned away from the Sun. Some gasses – especially methane and carbon dioxide – work like a blanket to keep things warm. In the past, the Earth has been much warmer and much colder than it is now. Since people have grown used to the heat we have now, though, we do not want the Earth to be too much warmer or colder. Most of the ways people create electric power use burning kinds of carbon—especially coal, oil, and natural gas. Burning these creates new carbon dioxide and can cause more warming. A large discussion is going on now about what people should do about the Earth's latest warming, which has gone on for about 150 years. So far, this warming has been good for people: plants have grown better and the weather has been better than when it was colder before. Some people who learn about science, though, say that many bad things will possibly come about if the warming goes on.
About seven billion people live on Earth. They live in about 200 different lands called countries. Some, for example, Russia, are large with many large cities. Others, for example, Vatican City, are small. The five countries with the most people are China, India, the United States, Indonesia, and Brazil. About 90% of people live in the north half of the world, which has most of the land. Scientists think that people originally came from Africa. Now, 70% of all people do not live in Africa but in Europe and Asia.
People change the Earth in many ways. They have been able to grow plants for food and clothes for about ten thousand years. When there was enough food, they were able to build towns and cities. Near these places, men and women were able to change rivers, bring water to farms, and stop floods (rising water) from coming over their land. People found useful animals and bred them so they were easier to keep.
Et cetera
Et cetera means "and the rest" in Latin. It is often used in English to continue a list that is longer than what can be normally written. People most often write "et cetera" as etc.. Very rarely, it is also written "&c" because the ampersand, or the "&", is the same as "et", having been formed by 'e' and 't' being joined into a single letter. It is also the symbol for "and". Some people write it as "ect", but that is wrong since it incorrectly abbreviates "et cetera".
Experiment
An experiment is a test of an idea or a method. It is often used by scientists and engineers. An experiment is used to see how well the idea matches the real world. Experiments have been used for many years to help people understand the world around them. Experiments are part of scientific method. Many experiments are controlled experiments or even blind experiments. Many are done in a laboratory.
Experiments can tell us if a theory is false, or if something does not work. They cannot tell us if a theory is true. When Einstein said that gravity could affect light, it took a few years before astronomers could test it. General relativity predicts that the path of light is bent in a gravitational field; light passing a massive body is deflected towards that body. This effect has been confirmed by observing the light of stars or distant quasars being deflected as it passes the Sun.
Now, a hundred years or so after Einstein published his ideas, there have been many tests, all of which have been consistent with Einstein's predictions. But, one day, we might find the theory has some limits beyond which it does not work. What we test are implications of the theory, because the theory itself is too large and complicated to test all at once.
A controlled experiment is a kind of comparison. It often compares the results from experimental samples against control samples. Control samples are the same as the experimental sample, except for one difference. This difference is the one thing whose effect is being tested (the independent variable). A good example would be a drug trial. The sample or group receiving the drug would be the experimental group (treatment group); and the one receiving the placebo or an older treatment would be the control group.
An observational study is used when an experiment would be difficult, unethical, or expensive. Observational studies are not experiments. Experiments can control for other variables, and it allows the researchers to change something. Observational studies often do not have random samples, and they often have many variables.
Ethics
Ethics is the study of good and bad behaviour. It is one of the main parts of philosophy. Ethics tries to answer questions like:
When discussing ethics, the philosophy is generally separated into:
"Morality" is what someone thinks or feels is good or bad.
There are many different moralities, but they share some things.
For example, most people think that murder (killing somebody) is wrong.(compare Exodus 20:13)
Some philosophers have hope to find more things that moralities share.
They think that ethics should use the scientific method to study
things that people think are good or bad. Their work can be used
to test the fairness of a situation, such as how people should treat
each other. An example of this kind of thinking is the categorical imperative.
Many countries have laws based on this idea of fairness.
Understanding ethics can help people decide what to do when they have choices. Many think that doing anything or making any choice is a part of ethics.
Ethics is part of other fields of study in many ways. Here are some ways:
Along with aesthetics ethics forms part of axiology, the philosophy of what people like.
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