Two Aquarium Galleries, One Watery Planet

Planning an Aquarium Water Exhibit

An aquarium is preparing an exhibit that compares its River Gallery with its Ocean Gallery. The River Gallery has fresh water, and the Ocean Gallery has salt water. For this project, the staff count only the water in these two displays, not water elsewhere in the building. Their planning records show 4,000 gallons in the River Gallery and 6,000 gallons in the Ocean Gallery. The staff will place a graph beside the displays so visitors can compare the amounts. The graph's bars use the same unit and the same scale. Each gallery name identifies the water included in that bar.

A second part of the exhibit will show water across the whole Earth. It will include water far beyond aquariums, homes, and towns. The staff use rounded scientific estimates to make a simple model: imagine all of Earth's water divided into 100 equal units. In this model, 97 units represent salt water and 3 units represent fresh water. Each unit represents one hundredth of the total, or 1%. These numbers are rounded, so they are useful for showing the broad pattern rather than an exact count. The Earth model and the aquarium records describe different collections of water.

The fresh water in the Earth model includes more than the water people can see flowing in rivers. It also includes fresh water frozen in glaciers and ice sheets, water stored underground, and water in lakes and other places. Frozen water still counts as water in the model. Water underground counts even though it cannot be seen from the surface. The exhibit team wants visitors to notice what each graph includes before drawing a conclusion. Visitors will make an Earth graph from the model's numbers and then compare it with the aquarium graph. Labels, units, and bar heights will help them explain what is alike and what is different.