This three-act film tells the story of the detective work that solved the mystery of what caused the disappearance of the dinosaurs at the end of the Cretaceous period. Shot on location in Italy, Spain, Texas, Colorado, and North Dakota, the film traces the uncovering of key clues that led to the discovery that an asteroid struck the Earth 66 million years ago, triggering a mass extinction of animals, plants, and microorganisms. Science practices in geology, physics, biology, chemistry and paleontology all contributed to the solution to this compelling mystery. Lesson plans are included that have students identify evidence and construct an explanation to tie it together. Summary questions are included at the end and a class discussion is recommended. (This activity will be the only one evaluated in this review.) Another resource is “Finding the Crater” where students “visit” different K-T boundary sites. There are also lessons where students analyze various characteristics of the asteroid such as its size and energy, chemical data about the asteroid, and the iridium fallout from an asteroid impact. A hands-on activity where students study the differences in foraminifera fossils below and above the K-T boundary is also included as well as an article that outlines more details about each of the discoveries covered in the film. You can view the film on the website or HHMI will send you a free DVD. Lesson plans including teacher notes and a student handout can be found at http://www.hhmi.org/biointeractive/following-trail-evidence. Other extensions can be found at http://www.hhmi.org/biointeractive/browse?kw=day+the+mesozoic+died