if a mole of marbles cover Beijing, how deep will the marbles be?

Area of Beijing: A ≈ 16400km²

 

Take standard marble diameter: d = 5/8"

 

Number of marbles of 1 marble depth required to cover Beijing: N ≈ A/d² ≈ 6.5*10¹³

 

One mole of marbles = Avogadro's number worth of marbles; Av ≈ 6*10²³

 

Depth of Avogadro's number of marbles on Beijing ≈ d*Av/N ≈ 1.5*10⁵ km  

 

They would reach about half way to the moon!