Natural history collections can be viewed as "libraries of knowledge" of the biological world, and specimens within those collections represent the "books" within the biological library. Museum specimens document organisms, past and present, occurring in a specific place and time. Preserving this biodiversity facilitates understanding the world in which we live and the changes occurring on Earth over time. These changes usually occur naturally based on environmental and biological influences. Other times change may occur due to the impact of humans invading a given area and impacting the plants and animals living in that region.