Images courtesy of NASA and NOAA These cylinders contain layers of ice, with each layer corresponding to one warming and cooling period, or one year. With these
samples, scientists can count the number of layers under the surface to determine when a layer was made. They can also
analyze a layer to tell what chemicals were abundant in the Earth's atmosphere when that layer was made
A scientist analyzes a sample of ice from a layer that is 2.500 layers from the surface. She finds that it contains an unusually high
amount of volcanic ash. The information from her sample suggests that a large volcanic eruption occurred on Earth about
years ago