If the same amount of matter exists before and after changing, then is Earth like a closed ecosystem? Does is it contain a specific amount of matter until an outside source adds more matter into it?
Earth is not 100% closed. We gather material from space (both asteroids and dust) as well as losing some material to space (mostly gas in the high athmosphere being pushed away by solar winds)
Also since matter can be created from energy and vice versa a small amount of matter is lost in nuclear decay processes.
But overall yeah, those are tiny amounts compared to the size of earth. For the most part you can assume the amount of matter on earth stays pretty constant.
We’re regularly losing and gaining small amounts of matter from atmosphere that gets skimmed off from solar winds, small bits of matter coming into the atmosphere even if it “burns up” on the way in, etc….
That said, for practical purposes in a human lifetime: yes, the total mass on earth is relatively constant since those changes are quite small relative to the total mass you’re talking about.
in terms of being closed, no, we receive vast amounts of energy from the sun, and lose equal amounts to space. in terms of matter alone, small amounts fall to us all the time, and rarely some matter escapes, but it’s very hard to get matter off earth.
the amount of matter we receive isn’t constant: we fly through different fields and get a few meteor showers a year. it also wasn’t constant in the past, when the solar system was forming vast amounts of matter were coalescing to form what we now call earth.
depending on how precise(theoretical) you want to get either yes or very very VERY slowly decreasing(maybe).
ELI5 yes that is exactly right we are part of earth and will return to become the next generation of earthlings like the dinosaurs and germs before us, while drinking the same water as them. That is until we rocket into space and we lose those atoms forever until some asteroids can come and add some spice to the mix.