Shulou(Shulou.com)11/24 Report--

About the measurement of the age of the earth, let's start with the story of a famous physicist who was hit in the face.

Of all the natural sciences, physics is undoubtedly the hardest and most revealing of the nature of the world.

In other words, if physicists argue with scientists in other disciplines about a scientific issue, physicists usually have the last laugh. But there are always exceptions. Physicists have also been "slapped in the face" by scientists in other disciplines. One of the typical examples of being slapped in the face is the famous British physicist Lord Kelvin.

Lord Kelvin, formerly known as William Thomson, was born in 1824 to an intellectual family in England. He is a child prodigy. He was admitted to the University of Glasgow at the age of 10 and became a professor at the University of Glasgow at the age of 22. Throughout his life, he published more than 660 scientific papers.

More importantly, he was one of the pioneers of thermodynamics and made a great contribution to the establishment of the first and second laws of thermodynamics; in addition, he invented the absolute temperature scale later named after himself. This made him one of the most famous physicists of the 19th century.

In addition to being famous in academic circles, Lord Kelvin Thomson is also a very successful entrepreneur. He set up a company to produce and sell a kind of nautical compass he invented; it soon became the largest supplier to the British navy, making him a lot of money. In addition, he set up an electricity company; so his home became the first house in Glasgow to be equipped with electric lights. More influential, he led a company that successfully laid the first undersea cable across the Atlantic.

Due to his outstanding contributions in academia and industry, William Thomson was canonized as the first Baron of Kelvin by the British royal family in 1892. But people are more accustomed to calling him Lord Kelvin.

Of course, there is no gold, no one is perfect. Lord Kelvin also played an own goal twice. The most famous oolong took place at the turn of the century in 1900.

In a speech that year, Lord Kelvin openly declared that the physics building had been built and that all that was left was simple tinkering. Although he mentioned that there were still two dark clouds floating in the sky of physics, he thought they were just two small problems that could be solved completely in no time. He was proved to be very wrong. At the beginning of the 20th century, those two dark clouds became two new physics edifices, namely relativity and quantum mechanics. This embarrassing story has even been written in junior high school textbooks in many countries, so that Lord Kelvin is still ridiculed by the world.

Another oolong played by Lord Kelvin was his miscalculation of the age of the earth. He estimated the age of the earth by thermodynamics: suppose that the earth was originally a huge fireball, which gradually cooled from the outside to the inside over time, thus becoming what it is today; and this cooling time is the age of the earth. In 1862, he published a paper claiming that the age of the earth was between 200 million and 400 million years old. In 1897, he published another paper claiming that the age of the earth was actually about 2400 years old.

You may wonder: why are the results of the two papers so different? This is because Lord Kelvin realized midway that, based on the theory of physics at the time, the sun could only burn for tens of millions of years at most. So he modified his theoretical model, which greatly reduced the age of the earth.

Soon, however, a group of unexpected people ran out and punched Lord Kelvin mercilessly in the face.

Sheldon Sheldon of the famous American TV series the Big Bang Theory, a rather conceited theoretical physicist, likes to belittle subjects other than theoretical physics. He particularly despised geology and even openly declared that geology was not a real science at all. Obviously, he doesn't know much about the history of physics. Because the people who came out against Lord Kelvin were a group of geologists.

You may want to ask: "how do these geologists calculate the age of the earth?" The answer is by looking at some ancient sedimentary rocks.

Sedimentary rock on earth, there is a very important type of rock called sedimentary rock. The structure of the sedimentary rock is layer by layer, and the lower the sedimentary rock, the older the age. By studying the deposition rate of a layer of rock, the time it takes to form the layer of rock can be calculated, and the time taken to form the whole sedimentary rock topography can be estimated by adding up the formation time of each layer of rock. Those geologists regard this time as approximately the age of the earth.

Many geologists have estimated the age of the earth in this way, and the number they have calculated is significantly larger than that published by Lord Kelvin. To cite two examples, Charles Darwin declared in the first edition of the Origin of species that the earth is at least 300 million years old, and Samuel Horton, a geologist at Trinity College, Cambridge University, claimed that the earth is as old as 2.3 billion years.

As a result, there are irreconcilable views on the age of the earth. Lord Kelvin believes that the age of the earth is only about 2400 million years. Geologists believe that the earth is at least hundreds of millions of years old.

Both sides have always been fair and reasonable, and women have always been reasonable. But in 1907, the emergence of a person completely upset the balance of the balance.

In order to explain the truth, I would like to tell you what "radioactivity" is. The so-called radioactivity refers to the phenomenon that unstable nuclei emit certain rays spontaneously and then decay into stable nuclei. In 1896, French physicist Anthony Becquerel was the first to discover the radioactivity of uranium.

Two years later, Pierre Curie and Marie Curie found that polonium was more radioactive. As a result, the three men shared the 1903 Nobel Prize in physics.

By the way, one more thing. The committee had intended to award the prize only to Anthony Becquerel and Pierre Curie. But Pierre Curie loved his wife so much that he insisted that Madame Curie be listed as the winner, otherwise he would not go to Sweden to receive the prize. After consulting Becquerel, the award committee made the following decision: Becquerel won a bonus of 1 and 2, while the Curies received a bonus of 1 and 4 each.

Fortunately for the winner of the 1903 Nobel Prize in Physics, Madame Curie was not buried by history because of Pierre Curie's insistence. In 1907, the man who broke the balance finally appeared on the stage. He is Ernest Rutherford, a famous British physicist.

In the field of physics, Rutherford is famous for looking down on other subjects. He once said such a famous saying: "all science in the world is either physics or stamp collecting." The implication is that compared with physics, other natural sciences are at the same level as stamp collecting. This sentence offended scientists in many other disciplines, among which chemists reacted most fiercely. In fact, they even "retaliated" against Rutherford by giving him a Nobel Prize in chemistry.

At the beginning of the 20th century, it was known that for radioactive elements, some of their nuclei would spontaneously decay into the nuclei of other elements, thus reducing the mass of radioactive elements.

In 1907, Rutherford discovered a wonderful phenomenon: for all radioactive elements, the time it takes for the nucleus to decay to only half (scientifically called the half-life) is fixed. For example, a radioactive element of 100 kilograms decays to only 50 kilograms, and the same radioactive element of 50 kilograms decays to 25 kilograms, which takes exactly the same time.

Ernest Rutherford's discovery is of great practical value. For example, if an antique contains a radioactive element, we can determine the age of the antique by measuring the ratio of the radioactive element to the element it eventually decayed.

In other words, we can use the half-life of radioactive elements as a standard clock to measure the age of ancient objects. In fact, the accuracy of measurement, whether it is Lord Kelvin's thermodynamic method or the geologist's method of sedimentary rock, is much worse than this method of using the half-life of radioactive elements.

By studying the decay of some ancient minerals, Rutherford found that the earth is at least 700 million years old. The result proclaimed a victory for geologists.

More importantly, Rutherford's discovery points the way for the measurement of the age of the earth. As long as you can find the oldest rock on earth, and then use the half-life of a radioactive element to calculate its age, you can estimate the age of the earth. Of course, exactly which radioactive element should be used is still an open question.

The next major contributor is the British geologist Arthur Holmes. Holmes is mainly concerned with an isotope of uranium, uranium 235. You should be no stranger to uranium 235, because it later became the main raw material for making atomic bombs. Uranium 235 is radioactive and can spontaneously decay to lead 207; more importantly, the half-life of uranium 235 is as long as 700 million years. So it can be used as an ideal clock to measure the age of the earth.

By determining the ratio of U-235 to Pb-207 in ancient rocks, Holmes published an article in 1927 claiming that the age of the earth was between 1.6 billion and 3 billion years old. In 1946, he published another article claiming that the age of the earth should be more than 3 billion years old.

In 1948, Harrison Brown, a professor of geology at the University of Chicago, also took a keen interest in the age of the earth. But he realized it was a big pit and didn't want to jump into it foolishly. So Brown handed over the task of determining the age of the earth to Claire Peterson, his doctoral student. In order to get Peterson to jump, Brown tricked him into saying that the subject was "easy". As a result, Peterson was tricked into coming in.

Claire Peterson, the Terminator of the difficult problem of the century, thus stepped onto the stage of history.

In the past, people used to measure the age of the earth to look for some very old rocks. But the problem is that the so-called ancient rocks were actually formed long after the birth of the earth. In other words, if you only study the rocks on the earth, you may greatly underestimate the age of the earth.

Peterson took a different approach and put forward a very bold conjecture: the meteorites that fell from space were actually building materials left over from the early days of the formation of the solar system, and their interior retained the most primitive chemical components of the solar system. In other words, these meteorites are actually as old as Earth.

In this way, as long as Holmes's method is used to determine exactly how many years these meteorites have existed, the age of the earth can be calculated. This wonderful idea, like a flying immortal, has brought a real dawn to solve the age of the earth in this century.

Of course, the road to success is often not smooth. In the actual measurement process, Peterson encountered a big problem: as soon as the meteorite samples were exposed to air, the content of lead in the samples increased significantly; in other words, these samples were easily contaminated by lead in the air. To deal with this problem, Peterson set up the world's first sterile laboratory at the California Institute of Technology, where he works. He carefully selected samples of ancient meteorites in a sterile laboratory and accurately determined the ratio of uranium to lead. His efforts finally paid off seven years later.

Photo Source: pexels1955 year, Peterson officially announced at an academic conference that the exact age of the earth is 4.55 billion years. This result has not changed much up to now. After nearly a hundred years of efforts, mankind has finally measured the age of the earth.

You might as well say a few more words about Peterson. Because measuring the age of the earth is not the culmination of Peterson's life.

After becoming famous, Peterson began to care about another question: why does the atmosphere contain so much lead? By studying the snow cover of different ages in Greenland, he found that the amount of lead in the atmosphere suddenly exploded in 1923. That year, three American giants (General Motors, DuPont and New Jersey Standard Oil) formed a joint venture called Ethyl gasoline and began to sell leaded gasoline to the world.

Since then, Peterson began a long struggle to protect the environment. He often publicly attacked ethyl gasoline companies and called on the government to legislate as soon as possible to ban the sale of leaded gasoline.

The counterattack of the ethyl gasoline company was very fierce. It uses all kinds of connections to prevent Peterson from getting any more funding for scientific research. In addition, it has put constant pressure on Caltech's board of directors to get Peterson out of his job.

This is an almost impossible task: an ordinary person has to fight against a huge interest group alone. Fortunately, Peterson didn't give up. Under his constant appeal, the awareness of environmental protection has gradually awakened in the hearts of the American people. In 1970, the U.S. Congress introduced the Clean Air Act; in 1986, the U.S. government banned the sale of all leaded gasoline. After decades of hard struggle, Peterson finally had the last laugh.

Author: Wang Shuang part of the image source network copyright belongs to the original author Editor: Zhang Runxin this article comes from the official account of Wechat: Origin Reading (ID:tupydread), author: Wang Shuang, Editor: Zhang Runxin

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