The water molecules now in your body were once part of a molecular cloud. Only about onemillionth of the mass of a molecular cloud is in the form of water molecules, and the mass density of such a cloud is roughly 4.0×10−21 {\rm g}/{\rm cm}^{3}

Question

Estimate the volume of a piece of molecular cloud that has the same amount of water as your body.

Answer 1

Assuming an average human body mass of 70 kg, the mass of water in the body is approximately 0.04 kg. Dividing this by the mass density of the molecular cloud (4.0×10−21 {\rm g}/{\rm cm}^{3}) gives a volume of 1.0×10−17 {\rm cm}^3.