Life is the most wonderful and fascinating natural phenomenon. Today, there are more than 6.5438+0.5 million species of animals, more than 400,000 species of plants and more than 200,000 species of microorganisms on the earth, which constitute a life world full of butterflies, birds and flowers, beautiful scenery, colorful reproduction and evolution, and endless life. From mountains to plains, from deserts to grasslands, from the air to rivers and lakes.
However, 4.6 billion years ago, when the earth was formed in the universe, it was not only hit by hundreds of millions of comets and meteorites, but also took about 654.38 billion years to lower the temperature by several thousand degrees Celsius. At that time, the earth was a lifeless and desolate world. After about 654.38 billion years, it seems that simple cyanobacteria appeared on the earth. Therefore, for the first time on earth, this is a question that people are generally concerned about the origin of life on earth.
The origin of life is an important scientific topic in contemporary times, but it is also the most basic biological problem that is little known so far. In this article, we will introduce several theories about the origin of life.
There have been various hypotheses about the origin of life in history, such as "God's Creationism" (that life is created by God or God) and "Spontaneous Generation" (that life, especially simple life, occurs naturally from inanimate matter). Most of these hypotheses are based on speculation and have been denied by people. Judging from the research papers put forward by the international conference on the origin of life held in recent years, contemporary hypotheses about the origin of life can be divided into two categories:.
The theory of chemical evolution holds that life originated from a series of chemical evolution processes from inorganic to organic and from simple to complex under the condition of primitive earth, while the theory of cosmic embryology holds that the original life on earth came from outer space of the earth and only developed on the earth later.
Chemical evolution theory
Biological molecules such as nucleic acid and protein are the material basis of life, and the key to the origin of life lies in the origin of these biological substances, that is, on the lifeless primitive earth, abiotic substances produce various organic substances and biological molecules through chemical action due to natural reasons. Therefore, the origin of life is first of all the origin and early evolution of primitive organic matter. The role of chemical evolution is to create a class of chemical substances, which constitute common "structural units" such as amino acids and sugars, as well as life forms such as nucleic acids and protein.
1922, biochemist Oberlin was the first to put forward a verifiable hypothesis, that is, some inorganic substances on the primitive earth became the first organic molecules under the action of energy from lightning and the national emblem sun. After a lapse of 3 1 year, American chemist Miller first experimented with this hypothesis in 1953. He is like the atmospheric composition on the primitive earth. Ammonia and steam, etc. Organic amino acids were synthesized by spark heating and discharging. After Miller, many other important biomolecules, such as purine, pyrimidine, ribose, deoxyribose, nucleoside, nucleotide, fatty acid, porphyrin and lipid, were synthesized under the condition of simulating the primitive earth. +0965 and 19865438+ insulin and yeast alanine transfer ribonucleic acid were synthesized for the first time in China. Protein and the formation of nucleic acid are the turning point from inanimate to living. The successful synthesis of these two biomolecules has opened a new era of synthetic life to study the origin of life.
Generally speaking, the chemical evolution of life includes four stages: from small inorganic molecules to small organic molecules; Forming organic macromolecules from small organic molecules; From organic macromolecules, a multi-molecular system that can maintain its own stability and development; From a multi-molecular system to primitive life.
Cosmic embryo species theory
In the past and now, many hypotheses belonging to the theory of cosmic embryo have been put forward. For example,1put forward at the 10th International Conference on the Origin of Life in July, 1993 that "the organic substances that cause chemical reactions and lead to life are undoubtedly brought by comets that collide with the earth"; Others infer that one of the comets that collided with the earth crossed the universe with a "life embryo" and left it on the newborn earth, thus giving birth to life on the earth. A few years ago, a space physicist and an astrophysicist also explained the origin of life on earth as: the source of life on earth may come from one or several comets that fell into the ocean four billion years ago, and they also believed that comets provided the raw materials needed for the birth of life on earth (they called them "comets").
Although some scientists have strong objections to this hypothesis (they think that "comets bring some substances, but they are not decisive, and the substances necessary for life already exist on the earth"), although this view is still a problem that needs further proof, through the exploration and research of organic molecules on meteorites, comets, interstellar dust clouds and other planets, we can understand the formation and development laws of those organic molecules and compare them with those on the earth.