十大科学问题科学发现英语原版
霜降节气
WHY IS THE SKY BLUE
年的作文"I e skies of blue and clouds of white," Louis Armstrong crooned in his 1968 song "What a Wonderful World." And he probably did, given that his song is an ode to optimism. European rearchers have discovered that light from the blue part of the spectrum influences the emotions in a positive way, making us more responsive to emotional stimuli and more adaptable to emotional challenges [source: Opfocus].
But we digress. The reason the sky appears blue is becau of an effect called scattering. Sunlight has to pass through the Earth's atmosphere, which is filled with gas and particles that act like the bumpers on a pinball machine, bouncing sunlight all over the place. But if you've ever held a prism in your hands, you know that sunlight actually is made up of a bunch of different colors, all of which have different wavelengths. Blue light has a relatively short wavelength, so it gets through the filter more easily than colors with longer wavelengths, and as a result are scattered more widely as they pass through the atmosphe
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re. That's why the sky looks blue during the parts of the day when the Sun appears to be high in the sky (though it's actually the spot on the planet where you are standing that is moving, relative to the Sun).
宝宝饼干HOW OLD IS THE EARTH
At sunri and sunt, though, the sun's rays have to travel a longer distance to reach your position. That cancels out blue light's wavelength advantage and allows us to e the other colors better, which is why sunts often appear red, orange or yellow [sources: NASA, ScienceDaily].
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piano的复数形式The Earth's age is something that people have been arguing about, at times bitterly, for a long, long time. Back in 1654, a scholar named John Lightfoot, who calculations were bad upon the Book of Genesis in the Bible, proclaimed that the Earth had been created at precily Mesopotamian time, on Oct. 26, 4004 B.C. In the late 1700s, a scientist named the Comte de Buffon heated up a small replica of the planet that he had created and measured the rate at which it cooled, and bad upon that data, estimated th
at the Earth was about 75,000 years old. In the 19th century, the physicist Lord Kelvin ud different equations to t the Earth's age at 20 to 40 million years [source: Badash].
But all that was trumped in the late 1800s and early 1900s by the discovery of radioactivity, which was soon followed by calculation of the rates at which various radioactive substances decay [source: Badash]. Earth scientists have ud that knowledge to determine the age of the Earth's rocks, as well as samples from meteorites and rocks brought back from the Moon by astronauts. For example, they've looked at the state of decay of lead isotopes from rocks, and then compared that to a scale bad on calculations of how lead isotopes would change over time. From that, they've been able to determine that the Earth formed approximately 4.54 billion years ago with an uncertainty of less than 1 percent [source: U.S. Geological Survey ].
HOW DOES NATURAL SELETION WORKS
高骊山Like the age of the Earth, the theory of evolution -- first developed by biologist Charles Darwin in the mid-1800s -- is another subject that people tend to get worked up about. If
you've ever en the classic movie "Inherit the Wind," you probably already know about the infamous Scopes Monkey Trial of 1925. Famous attorney Clarence Darrow argued unsuccessfully upon behalf of a high school biology teacher named John Scopes, who was accud of violating a Tenne statute that
banned anyone from teaching that humans were descended from "a lower order of animals," and decreed that the Biblical story of creation was the only acceptable explanation [source: Linder]. In recent years, it's been anti-evolutionists who've fought in court and in legislatures for require that children learn "creation science" in school, in addition to evolutionary theory [source: Raffaele].
And if there's an idea that particularly bugs anti-evolutionists, it's Darwin's central concept, which is called natural lection. It's really not a difficult idea to understand. In nature, mutations -- that is, a permanent change in the genetic blueprint of organisms, which can cau them to develop different characteristics from their ancestors -- occur randomly. But evolution, the longer-term process by which animals and plants change ov
er multiple generations, is not up to chance. Instead, changes in organisms tend to become more common over time if the change helps the organism to better survive and reproduce.
For example, imagine that some beetles are green, but then, a mutation caus some beetles to be brown, instead. The brown beetles blend into their surroundings better than the green beetles, so not as many of them are eaten by birds. Instead, more of them will survive and reproduce, and may pass along the genetic change that will make their offspring brown. Over time, the beetle population will gradually shift to being brown in color. That, of cour, is the simple version. In practice, natural lection is bad upon averages, not specific individuals, and it's not quite as smooth and orderly of a process [source: UC Berkeley].
WILL THE SUN EVER STOP SHINING
This question reminds us of another pop song, Skeeter Davis's 1962 single "The End of the World," in which the singer wonders why the sun keeps on shining after her boyfriend
apparently has dumped her. The conceit of the lyrics is that the reality around us -- whether it's the shining sun or the birds singing in the trees -- is more durable than our fragile little feelings. In truth, though, our lovelorn lass had the misfortune to be born too soon -- by about 5.5 billion years, give or take a few. That's the point at which the sun, which like any other star is a gigantic fusion reactor, will run out of the hydrogen in its core that it burns as fuel to create sunshine and will start burning the hydrogen in its surrounding layers.
