Mass: Creation & Destruction - What Does it Mean?

[ThomasFuhlery]

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?

 

[HallsofIvy]

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?

Yes, it is true that the Earth gains mass every year from meteorites- not very much compared to the mass of the Earth itself. No, "more people born every year" (not to mention animals, plants, etc.) do not add mass. As you say, that's just recycling: a baby's mass comes from the food it's mother eats. While growing a person (or animal, plant, etc.) gains mass because the food it eats has mass (and the oxygen taken in, etc.). Except for the small amount of mass added by meteorites (and I guess we now ought to subtract the mass of space probes sent out) the mass of the Earth is a constant. What does that mean for the future? Basically that it is "steady state" and things (well, the mass of the earth) will stay about the same. Of course, it also means that the Earth's "biosphere" is a closed system and very bad things can happen if you pollute a closed system.