They mention that water already on earth would have boiled off in its youth. I don't understand this, wouldn't the vapor stay around the planet, then return to liquid when the planet cooled?
Or else, what would have attracted the water away from the earth's atmosphere? And if so, why wouldn't it have attracted away the azote and oxygen and all of the atmosphere at the same time? Or was there not yet an atmosphere?
Simulations do not like this scenario. The gravity is not enough to counter the expansion due to the heat, so the water (vapour) leaks off far and wide with little chance of coalescing in the inner solar system.
Yeah, that doesn't make sense. Venus is a good deal smaller and was able to hold a dense atmosphere, so Earth should be even more able to hold water vapor. Probably lost most bare hydrogen though.
Or else, what would have attracted the water away from the earth's atmosphere? And if so, why wouldn't it have attracted away the azote and oxygen and all of the atmosphere at the same time? Or was there not yet an atmosphere?