Answer:  

Dr. Satoru Nakashima, who is actually studying “origin of life based on material interaction”, kindly answered the question above.
 
 
It is a very hard question to answer. Even the researchers in this particular field do not have a concrete answer yet. I will try my best, however, to explain as clearly as possible.
 
Why are living creatures made of carbon atoms?
 

1. The universe consists of 70.0 % of hydrogen (H), 28.0% of helium (He), 0.92 % of oxygen (O), 0.34 % of carbon (C), and 0.12 % of nitrogen (N). Living creature use all of these but helium. Since helium is an inert gas and does not react with other elements, it is not suitable for living creatures. I assume that we, the living creatures on earth, originally came from the outer universe.
     

2. Hydrogen, oxygen, carbon, and nitrogen are abundant in the universe, and they are the basic elements for organic molecules. Probably organic molecules were formed in various locations in the universe. Among these four elements, only carbon atoms have four arms for bonding and are able to combine with hydrogen, oxygen, nitrogen, and carbon in various manners. As a result, a variety of organic molecules with different chemical reactions and functions would be created.
    

3. From organic molecules to living creatures (chemical evolution)
    
   It is assumed that some organic molecules (mainly small molecules) had already been created in the universe. It is, however, not easy to bond small molecules together and create polymers. External energy or some catalysts are necessary to do that. 
   
   We assume that the following chemical evolution had been taken place, but it needs further research:
   
   Small organic molecules → Polymers → Polymers gather together and create the functions of life.
   
   The organic molecules, whose main structures are made of carbon atoms, seem to polymerize and become complicated polymer substances such as protein (folded structure) and DNA (double helix). They seem to hold the key to the various functions (e.g. enzyme, genetic information) that are essential for life.

  
Is it possible to form a living creature using other atoms, such as silicon?
 

1. First of all, there is not so much silicon in the universe. Silicon seemed to exist in some certain areas, and they accumulated, collided, and unite with one another, forming an “earth-type planet” which is rich in silicon.
     

2. Silicates, which are mainly made of silicon atoms, were formed on the planets such as earth. They are rocks. 
    
   Silicate minerals (e.g. quartz) have silicon chains with some oxygen, and there are other ions such as sodium and potassium in between.
    

3. It requires fairly high temperature and pressure to alter the structures of minerals, glasses and magmas which are made of silicon atoms. So it is very difficult to change the structures in accordance with the environment. 
    

4. However, silicon is very important as silicon semiconductors used in electronic circuits. So a new silicon creature, which has only an electronic brain, might be possible. 

  
Acknowledgement
We would like to thank Dr. Satoru Nakashima for his kind answer.
  
 
This article is translated by Chemistryquestion.com from the original article in Chemistryquestion.jp.  Please let us know if you find any errors.