We assert that you own your labor since you own the activity resulting from your living. The act of acquiring already pre-existing matter and energy around is ones own and thus we say one owns his body; the act of acquiring itself is labor. It is not the pre-existing matter and energy itself that is owned, but the activity that got mixed into it producing higher orders of organization. This activity is not a vague notion but rather can be described scientifically through entropy and information. "As entropy quantifies the degree of disorder in a system, any envisioned lifeform must have a higher degree of order than its supporting environment." (Azua-Bustos, Vega-Martinez, 2013) This is how we recognize the existence of life in other planets.
When people say they own Land however (for example, because of scarcity), they are making a claim that is quite different. They are claiming that the already pre-existing matter and energy itself is owned. But how do you do that without employing mere force or threat of force? It is a kind of ownership that is through aggression or backed by aggression rather than an ownership through created labor. How does one reserve land for ones self indefinitely without a guarantor who is willing to exact force on behalf of that person? Or how do you own land absolutely, in the right-libertarian sense, without a monopoly of force - or ironically, a State?