Assuming mass has not accreted from elsewhere, why would you think that there would be a mass change just because at different times it is in different forms (mineral --> plant --> animal --> mineral)?
Now, here is something to chew on: Perhaps the earth (and other planets and stars) IS increasing in mass. That it has increased substantially over millions of years. This has been posited because of zero point energy conversion to matter at the cores (centers) of celestial bodies.
Consider that the largest land animals today are elephants. They cannot run or jump. (But they can shuffle faster than humans can run.) How, millions of years ago, was it possible for dinosaurs to be much larger than elephants and other land animals today? Today, it is not be possible for animals of that size to exist because their bones and musculature would not be able to support them against the larger gravity (due to larger earth mass) of today.