Carbon, Silicon, Life

In terms of valency, silicon resembles carbon. Both have the valency of four. However, silicon cannot substitute carbon in most of the instances from chemical or biochemical perspective. The percentage of silicon in human body is only minuscule unless we consider someone like Pamela Anderson. Next to oxygen, carbon is the most abundant element by mass in human body. Outside body - if we consider earth's crust - silicon is the most abundant element by mass next to oxygen. Thus, if carbon represents the life forms, silicon represents the non-life forms (inanimate). 

Despite the abundance of silicon in the environment, the evolutionary process has chosen carbon to develop life forms. In other words, the 3 billion years old evolutionary process has essentially discarded silicon while developing life forms. Evolution is the most intelligent phenomenon happened on earth and it has chosen carbon. Strangely our mythologies say the opposite - from clay to man! Life form can change into clay - it is scientifically possible. Petrified trees are now part of every museum, tree turned into stone, not vice versa!

Carbon is a unique element and the proteins (enzymes, muscles, etc), DNAs, hormones, neurons and almost every vital thing in our body stand as an evidence for carbon's versatility. 

Silicon cannot compete with carbon in its versatility even though mimicking our neural network using silicon should be possible at least in future. For that matter, any element which has similar conductivity properties should be able to do. People have successfully replaced silicon at least in laboratory level, for example, with molybdenum or carbon nanotubes.  I would agree that silicon may create intelligence, may be by passing Turing test. However, silicon cannot form (or be a part of) life. 

Of course, it depends on how we define life! The scientistsmay define it as a form which is self sustainable, having organic unity, reproducible and responsive to stimuli. They keep adding many other features. However, it still remains impossible to fit all life forms into these definitions and one or two forms always remain as exceptions. I wonder how these scientists forget one important phenomenon, death. They all think about sustainability ignoring the fact that destructibility is also a part of life - it is at least a part of life of all the life forms we know.

To me life is defined by death. Something that cannot die cannot be a life form. You can break a robot, but you cannot kill a robot. This definition is applicable to any life form on the earth. 

No life form can survive death. If it is the case with earth, it should be the case with the universe too. No celestial body contains any element that cannot be found on earth. Helium was first discovered on the sun, not on the earth. The discovery was made from India (but not by Indians)! The scientists thought that they had found one extraterrestrial element that was not located on earth. Later helium was also found to be available in uranium ore on earth itself. It is an example to say that the earth is the face of the universe. What we have here could be the best that the universe has offered. It will keep offering more.