Answer is 4 ½ billion.
Scientists think the earth's age is 4 ½ billion. This calculation is based on the radioactive dating. Since the formation of the earth, the time period has been divided into 3 major geological time periods as eon. They are phanerozoic, proterozoic and archean. 
 
        
                    
             
        
        
        
In order to solve this, we need to know the standard cell potentials of the half reaction from the given overall reaction.
The half reactions with their standard cell potentials are:
<span>2ClO−3(aq) + 12H+(aq) + 10e- = Cl2(g) + 6H2O(l) 
</span><span>E = +1.47 
</span>
<span>Br(l) + 2e- = 2Br- 
</span><span>E = +1.065
</span>
We solve for the standard emf by subtracting the standard emf of the oxidation from the reducation, so:
1.47 - 1.065 = 0.405 V
        
             
        
        
        
You need to find the whole molar mass of the compound using the periodic table to add the values. 
Na2CO3= (2 x 23.0) + 12.0 + (3 x 16.0)= 106 g/mol
H2O= 10 x [ (2 x 1.01 ) + (16.0) ]= 180.2 g/mol
the total molar mass is 106 + 180.2 = 286.2 g/mol
the percentage of water you can find by doing "parts over the whole"
H2O%= 180.2 / 286.2 X 100= 63.0%
        
             
        
        
        
Explanation:
For example, Identify the number and type of ions formed in a reaction of calcium and carbon. Step 1: Determine the number of valence electrons for each element and whether the element loses or gains electrons. Calcium has 2 valence electrons and is a metal so it will give up two electrons.