Geologists take core samples of soil and rocks on Earth and examine the core samples to learn things about Earth’s history. The core samples can tell them about the climate or the types of animals that were alive at a certain time. They can even figure out when volcanoes erupted in the past by looking for layers of volcanic ash. Core samples can also be used to learn about other planets and bodies in our solar system. NASA missions have gathered core samples from the Moon and Mars for future analysis. Like the Earth, candy bars have multiple layers of different ingredients. When you take a core sample using a clear straw, you can see the layers.