Density Grams or kilograms
Volume is liters milliliters or cm cubed
If there was more water area and less land more animals would adapt to the water life than land. Like for example more evolving fins or even amphibians
just staying in water and no longer needing legs or the things they use for living on the land.
The mass of Hydrogen is 2 g/mol
The mass of Helium is 4 g/mol
