What we are?

More than 96 % of body weight is only 4 chemical elements: carbon, oxygen, hydrogen and nitrogen. They are the basis of life. Very important are also sulphur and phosphorus. Body contains a number of other elements like metals (calcium, potassium, sodium, magnesium, iron, copper, manganese, zinc, aluminum, lead and others)and non-metals (chlorine, iodine, fluorine, bromine, silicon and others). It is sometimes said that the body contains almost all elements of the periodic table. Most of these elements are found in the body in very small quantities. They are called micronutrients.
Let us return, however, to the four basic elements that make up more than 96 % of our weight. Most of them have oxygen, which one provides about 3/5 weight of the whole body. Followed by carbon - about 1/5, hydrogen is about 1/10 and nitrogen - about 1 /25th of our mass. Elements of these free well known to us. Carbon is carbon, graphite, diamond (we know that free carbon occurs in three forms), oxygen, hydrogen and nitrogen gases. It is clear that our body does not consist of diamonds and gases, and of complex compounds of four major elements with a number of others. Therefore, given the ratio of oxygen, carbon, hydrogen, and nitrogen may not reveal the essence of life. If we had based their ratio not by weight, and the number of atoms, it would be that the light of these elements - hydrogen - spread in the body the most.
So, its atoms in the body more than all other atoms together. However, as already mentioned, it is not the case, and in those chemical compounds that make up our body.
Most of all in the body of water - up to 2/3 of the mass. Water, as we shall see, is absolutely necessary for life, but it is still of secondary importance.
The main role belongs to the third of our body mass, which is its so-called dry residue. The main compounds are proteins, fats and carbohydrates, as well as related substances. All these substances are so characteristic of living organisms, in what has been called organic. "Skeleton" of complex molecules of these substances are long chains of carbon atoms, and therefore the carbon can be considered the most important of chemical elements of the living body. It is the ability of the carbon atoms be joined together in a long chain led to the emergence of complex organic compounds whose molecules sometimes in the hundreds of thousands of times more than the molecules of inorganic compounds, and therefore have a much more significant and unique chemical features.
If schematically imagine a molecule of protein, fat or complex carbohydrates in the form of a tree, we can say that the trunk and main branches of its forms an extensive chain of carbon atoms, and the "leaves" are the atoms of hydrogen and other elements. In places the "branch" of the tree role of "nodes" play a greater part of the atoms of oxygen and nitrogen, as if holding branches of the carbon chain.
Complex organic substances are found only in living organisms, in their secretions or residues. Hence arose in the views idealistically minded people a sharp line between living and inanimate. So if the first link, connecting both of the world, was that in a living organism there is not a single chemical element, which would not be in the inanimate nature (i.e., the basis of animate and inanimate bodies uniform), the second such link has been proven by scientists the opportunity to get organic matter in the laboratory by simple reactions between inorganic substances. At first it was established in respect of urea, and then were synthesized and more complex connections. Scientists already know how to create carbohydrates, fats and approached protein synthesis. The obtained data allow to understand, as was the development of organic substances from inorganic nature.
Well-known specialist in the field of the problem of the origin of life academician A. I. Oparin indicates that the development of this began with education in the Earth's atmosphere hydrocarbon compounds of carbon and hydrogen, first, and then more complex. Join these, being very active chemically react with water vapor in the atmosphere and waters that covered a considerable part of our planet (the so-called primary ocean). As a result of interaction of hydrocarbons with water to their molecule joined the oxygen atoms; there was alcohols, aldehydes, organic acids and finally substances type of simple carbohydrates and fats. As is known, carbohydrates and fats are composed of only three elements: carbon, hydrogen and oxygen. But, of course, of particular importance was the formation of organic substances containing nitrogen, since nitrogen is a compulsory component of the protein. In the atmosphere of the early Earth was much ammonia and when interacting with the above derivatives of hydrocarbons are formed nitrogen-containing amino acids. Meanwhile, amino acids are the building blocks of many thousands have created the "building" of a protein molecule. There are only about 30 different amino acids, but are connected together in a different order, they create a countless variety of naturally occurring proteins. The interaction between the amino acid dissolved in the primary water of the ocean, led for many millions of years to the formation of the first proteins. The emergence of proteins that are able to engage in the exchange of substances with the environment, marked the appearance on Earth of a new form of motion of matter - life.
It is necessary to emphasize once again that the process of development was millions of years. The chemical reaction between complex organic substances occur in normal conditions it is extremely slow. This is what causes chemists to create complex substances are not the ways in which they were created over millions of years nature, and to look for a special, "fast" way.