Oil, here is another analogy for you to attempt to get your head around. Take a litre of water and boil it in a saucepan, eventually that litre will not exist in the saucepan any more as it will evaporate. Pumice is formed by the molten rock "boiling", gases are escaping and only when the molten rock cools does it form bubbles. Now you might state the rock is expanded, however the amount of Gases that have evaporated into the atmosphere are high. Obviously the Earth's core and Magma are continuously hot enough to evaporate gases, some energy is lost into geothermal gieser's. This loss means that if there was even the smallest growth in regards to what you suggest, it would be lost elsewhere. I guess you can say the Earth is "Flat" as opposed to "Open".
No, Like I said it's "Flat". As it degasses bubbles are trapped so a volume can be maintained as it loses some (not alot) of mass. [Obviously the Earth's mass is added to via external entities (Meteorites) and plantlifes "photosynthesis" could actually also convert photonic energy into mass not just use it as a catalyst for cellular changes (However this could prove to be untrue). Albeit if it was true it would explain how the very surface of the earth's crust has developed over billions of years. This would suggest an "Open" system but since we are just dealing with the Earths internal Mechanisms, it's "Flat"]
