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  Chemistry timeline
     
c. 13.7 billion years ago
 
Narrative history in HistoryWorld     
Hydrogen and helium nuclei form in the first three minutes, with perhaps another 300,000 years before they combine with electrons to form atoms       
c. 13 billion years ago
 
Narrative history in HistoryWorld     
As gravity exerts its pressure within parts of the expanding fireball, subnuclear particles merge into more complex elements       
c. 450 BC
 
Narrative history in HistoryWorld     
Empedocles states that all matter is made up of four elemental substances - earth, fire, air and water       
c. 420 BC
 
Narrative history in HistoryWorld    
The Greek philosopher Democritus declares that matter is composed of indivisible and indestructible atoms      
c. 380 BC
 
Narrative history in HistoryWorld     
A Greek text, attributed to Polybus, argues that the human body is composed of four humours       
c. 300 BC
 
   
Epicurus postulates a universe of indestructible atoms in which man himself is responsible for achieving a balanced life