So, we've gone off to another star system and decided to build a Dyson bubble--a continuous statite, supported by radiation pressure, surrounding a star--with a surface gravity of 1g to live on.
Now, clearly, the bubble has a total surface area of hundreds of thousands of Earths--plenty of space! Except... we don't actually get to use all of that. Since the ground is held up by radiation pressure, we can't exceed a certain maximum areal density. Colonies have to be built in widely-separated dimples, with unobtainium cables spreading their weight over an enormous surrounding area. So, to figure out what kind of living area we'll actually have available, it's not sufficient to just know how much total surface area we have to work with--we need to know how many multiples of Earth's biosphere's mass we can support.
And to do that, we need to know how much the ecosphere--or at least the portions of it necessary to support human life, if that's less than all of it--actually weighs.
So, if we were to leave all of the mantle rock and metal behind and just strip off the life-supporting surface of the planet, how much would it weigh?