First, fill the jar's bottom with sand a few inches deep.

Color the water light blue. Slowly pour water into the jar, so it fills it about 2/3 full.

Slowly pour in the oil until about an inch from the top of the jar.

Squeeze a thick layer of foam shaving cream around the inside edge of the jar to resemble puffy clouds. Squeeze a very thin layer on the top of the oil in the center of the jar opening, leaving one or two little holes with no shaving cream. The little holes with no shaving cream make it much easier to drop stuff into the jar.

Now it is time to start the density experiment: The sand represents the ocean floor, the water is the ocean water, the oil is the sky, and the white shaving cream is the clouds.

If you are using glitter, sprinkle that over the shaving cream to represent rain. It will not go through the shaving cream, so that means the rain is still stuck in the clouds.

Sand is heavier than water, water is heavier than oil, and oil is heavier than shaving cream, so that is why the density jar is layered that way. Start dropping in ocean objects to see which will go down in the sand, which will float in water, and which will float in the oil. It all depends on the weight of the objects we are using. I had some ocean objects on the sand, some floated in the water for a few minutes, and the whale and the sea plant floated in the oil.