has a history of 4.6 billion years since its birth, and the age of the earth is about 4.6 billion years. Humans are composed of atom , so does it also mean that the lifespan of atoms in human bodies is 4.6 billion years?
This is a very interesting question. Dig deeper, is the lifespan of the particles that make up the macroscopic object the same as the lifespan of the macroscopic object? Does atoms have a lifetime? What is its lifespan?
In order to explain this problem clearly, we first start from other aspects.
What types of atoms are mainly composed of the human body?
Whether it is the white clouds floating in the sky or the horses running underground, they are all made of atoms, and the entire solar system is also made of atoms.
includes artificial and naturally occurring. Currently, humans have discovered 118 elements, and there are more than 90 natural elements on the earth. The carbon-based life on the earth is mainly composed of 28 elements. The human body is mainly composed of 11 elements: oxygen, carbon, hydrogen, nitrogen, phosphorus, sulfur, chloride, potassium, sodium, calcium and magnesium. They account for 99.9% of the total mass of the human body. In addition, the human body also contains more than a dozen necessary trace elements.
Here we need to explain that there may be several isotopes for the same element of ( proton number the same, neutron number different), one of which we call nuclide , and a nuclide corresponds to a kind of atom.
For example, hydrogen element, it is the simplest element in the universe, and it has three isotopes. In the universe, hydrogen exists in the form of three isotopes: hydroxide H, deuterium D and tritium T. Among them, hydroxide is a nuclide of hydrogen element. Its relative abundance of in nature is about 99.985%. What we usually call hydrogen atom refers to hydroxide. It consists of an proton and an electron. The mass is 1. It is the simplest atom in the universe. Deuterium is composed of a proton, an neutron, and an electron, with a mass of 2 and a relative abundance of about 0.015%; as for the relative abundance of tritium, it is less than 0.001%, with a mass of 3, and atomic nucleus, contains one proton and two neutrons.
The above figure is a schematic diagram of atomic structure of diphtheria and deuterium
atoms have long and short lifespans
atoms are not infinite, the lifespans of different types of atoms are different. The lifespan of atoms is theoretically equivalent to that of the universe. The lifetime of unstable atoms is different, with a length of up to billions of years and a shorter than a few seconds.
atoms are composed of protons, neutrons and electrons. The lifespan of atoms that stabilize elements can be estimated by the average lifespan of these particles. Among them, the average lifespan of electrons is infinite, the average lifespan of free protons is at least 10^35 years, and the average lifespan of free neutrons is about 15 minutes. However, under the constraints of the nucleus, the lifespan of neutrons will become very long, and neutrons can also stabilize the nucleus. It is generally believed that protons are very stable and do not easily decay, and their lifespan is longer than that of the universe. It can be seen that the lifespan of the atoms of the stable elements composed of these particles is also very long. If no accidents occur, it will be almost as long as the lifespan of the universe. The lifespan of an atom that is unstable varies greatly. All radionuclides are unstable. They spontaneously decay into stable atoms in the form of particles or rays emitted to the outside world. The elements in the periodic table of elements with atomic number (or proton number) 84 and later are radioactive element . Many stable elements also have radioactive isotopes, which will be transformed into stable elements through decay.
For the lifetime of radioactive elements, that is, the lifetime of unstable atoms, we can use half-life to describe it.
The picture above shows the half-life of some nuclides
So what is half-life ?
half-life is for radioactive elements (more accurate, it should be called radioactive nuclei). Only radioactive elements have half-life. For example, the isotope of carbon element, carbon 14, has a radioactive half-life of about 5730 years, which means that after 1 kilogram of carbon 14 atoms, there are only 0.5 kilograms of carbon 14 atoms left, and the other 0.5 kilograms will decay into stable nitrogen 14 atoms.
The lifespans of different nuclides of the same element are also very different. For example, the isotopes of the polonium element, Polonium 210 and Polonium 215, one half-life is as long as three months, and the other is only 0.00018 seconds. Among the three isotopes of hydrogen, tritium is radioactive and has a half-life of 12.33 years.
Atoms Creation and Destruction
One atom can become another atom through nuclear reaction . The methods of nuclear reaction include nuclear fusion , nuclear fission, decay of the nucleus, and particle bombardment.
The earliest batch of atoms in the universe originated from Big Bang . At that time, the main element in the universe was hydrogen, and hydrogen would form stars under the action of gravity. After the first batch of stars in the universe age and die, they will throw out a large number of new elements (such as carbon, oxygen and other elements).
The galaxies in the universe are mainly composed of stars. Each star is a nuclear fusion reactor, creating new atoms all the time. In addition to hydrogen, light elements such as iron are almost all produced in the melting pot of stars. When a star reaches the end of life, a supernova explosion may occur under the action of gravity, and the heavy elements behind the iron are formed in just a few seconds.
If there are no stars, there will be no sufficient raw materials to form the earth, and life will not be born. The earliest batch of atoms in the universe are hydrogen atoms, and other atoms are formed by fusion of hydrogen atoms on this basis.
89% of cosmic rays are free protons, and 10% are alpha particles (i.e. helium 4 nucleus). Protons and electrons will spontaneously combine to form hydrogen atoms. In addition, cosmic rays may undergo nuclear reactions with other atoms.
For stable atoms, we cannot determine its age; only the atoms of radionuclides can determine age
There are no two identical leaves in the world, but from the perspective of the microscopic world, this is not the case.
determines the number of nucleons. Different proton numbers correspond to different elements, and different neutron numbers correspond to different nuclides. We cannot label the same stable atoms, that is, they are completely homosexual.
For example, two hydrogen atoms, we cannot tell which one is newly generated, which one is later, and how many years have they been going through.
For radionuclides, we can judge its approximate age by measuring its decay. It is based on this principle that scientists can use radioisotopes to date ancient organisms and can also be used to identify antiques.
As shown in the figure, the dating range of different radioactive elements
conclusion
6666% of the human body is water, and water is composed of hydrogen atoms and oxygen atoms, and the hydrogen atoms in water are likely to be born in the past few million years. There are some other elements, which are most likely just born recently. In addition, the human body also contains trace amounts of radioactive isotopes. In fact, not only are there in the human body, but radioactive isotopes are distributed everywhere in nature. However, the radiation dose is very small and cannot be detected at all, and it is not harmful to the human body itself. The radioactive elements in these human bodies will also decay, and their lifespan will definitely not be several billion years.
It can be seen from this that not all atoms have a history of billions of years like the earth. Atoms also have creation and elimination, and atoms also have lifespans. It is incorrect to one-sidedly believe that atoms in our body have a history of billions of years.
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