From a crystal cave filmed for the original “Journey to the Center of the Earth” to seven weeks in Antarctica, Linda Welzenbach, senior research associate with the National Planetary Institute, took North Hall Middle School students across the planet and through millions of years Friday morning. Welzenbach spoke to Russ Crain’s sixth-grade science classes and to eighth-graders in the Edison-Earhart Exploration Academy. She was the Smithsonian Institution’s National Museum of Natural History’s collections manager for 15 years.