The Layout

So I am starting a project with some of my fellow students. We are making a ecosystem in a pop bottle. Our goal is to grow some onions in the bottle and have a worm survive for the rest of the school year and maybe beyond. The layout of our bottle consists of having two inches of gravel at the  bottom of bottle filled with water to the top of the gravel. Then we will have rich soil filled from the top of the gravel to the middle of the bottle. In the dirt there will be micro-organisms working the soil. There will also be a worm keeping the soil fresh. On the top layer of the soil we will plant onions somewhat near the edge of the bottle so we can watch them grow. Then the rest of the bottle is room for the onions to grow and for air space. That is our ecosystem in a bottle layout.