I've had a terrarium in a sealed mason jar on my desk at work for 2 or 3 years now and have never once opened it. It seems like everything grows much much slowe

I've had a terrarium in a sealed mason jar on my desk at work for 2 or 3 years now and have never once opened it. It seems like everything grows much much slower in there. There's some type of grass that has maybe grown 2 inches in that time and a leafy plant that hasn't grown appreciably either. The leaves don't really fall off, so decomposition is at a minimum. Perhaps the waste products of decomposition keep the bacteria and whatnot in balance.