This word has a special meaning in mineralogy — or the study of minerals. To mineralogists, an inclusion is any material trapped inside a mineral as it forms. That material could be a rock trapped inside another rock. It can be a bug or a feather stuck in a glob of amber. It could be a bubble of gas trapped inside a gem. Inclusions can reveal important insights about the ancient world. For example, an insect trapped in amber can tell scientists a lot about what life was like when the amber formed — all the way down to a bug’s last meal. Climate scientists are interested in inclusions in other substances as well. They look for inclusions of gas bubbles in ancient ice cores or salts. Those bubbles can tell scientists what the Earth was like long ago.