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I sometimes ask the deep philosophical question, why does a tree not sink into the ground it grows out of? It blows people's minds when I explain that the reason is because the tree is mostly water and CO2, a gas and a liquid coming from the sky.

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Trees don't sink into the ground because (a) a tree's root system is as large in the ground as it stands out of the ground and (b) the pressure of the weight of the tree is distributed across the (large) surface area of that root system.

Trees aren't light, by any stretch of the imagination. That solid mass is mostly water. Try lifting up a 1' or 2' section of a tree trunk that's 1-2' in diameter sometime.

I believe gp meant, "if the bulk of a tree's mass comes from dirt, why isn't the dirt around the tree used up as the tree gains mass?"

That's because the ground doesn't hold up trees, trees pin down the ground. Also, trees grow into the ground, not out of it.

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