Each of these words _can_ mean the same thing. The solid surface of the planet, the dirt. The slight distinction between the three can generally be thought of as: The earth is a generic term for the solid surface of the planet. The ground is a very localized area of the earth. Think "right below your feet". And land is used to refer to a specific area of the planet, but more generic than ground. It's a confusing distinction to try to explain. Please let me know if I didn't explain it well enough. Earth can also refer to our planet in general.

They are quite similar, but you do use them for different things. To me - ground is about a physical level. Above ground, below ground, at ground level. There is also an electrical term meaning a similar thing. Earth can be the whole planet, or the soft material at the surface (i.e not rock). Electrically, it is usually the same as ground. Land usually refers to an area. 'The land enclosed by the fence'. 'How much land have you got?'