The illustration shows the ecological change occurred in Glacier Bay of Alaska, after a retreating glacier exposed barren rock. Basis time, drawing is divided vertically in to five sections using dotted lines.

1. Within 15 years - Bare rocks can be seen.
2. Between 15 to 35 years - Grass started to grow.
3. Between 35 to 80 years - Small plants started to grow.
4. Between 85 to 115 years - Trees started to grow.
5. After more than 115 years - Hemlock and spruce forest are currently found in the area.