this might be a physics question, but... I don't understand something about thermodynamics. About how mass cannot be destroyed or created, really. They say that the earth gains mass every year from meteorites, right? And more people are born every year, and grow, etc., adding mass to the planet as well (and I understand that this is just the movement of mass from, say, the food they eat and what-not), but does that mean that the rate of death and decay of life is exactly proportional to the rate of birth, growth, and consumption of living things, or are we consantly gaining (or losing) mass, on earth? And if so, what does this mean for the future?