In addition to his many famous writings , Henry David Thoreau (1817-1862) took careful notes about the natural world around him. For example, on his daily walks he recorded the exact date when wildflowers of various species bloomed each spring. Today, biologists are using his notes to investigate long-term changes in the biology of Walden Woods. For example, in 2008 Biologists at Harvard University published an article in the Proceedings of the National Academy of Sciences  about how climate change is impacting the forest where Thoreau lived. Last year a team of researchers from Boston University published an article in PLoS ONE  which focused on how climate change has caused record-breaking early blooming dates of spring wildflowers.
Thoreau had no way to predict that his notes would be used as they are today. His notes, which scientists now view as a historic data set, serve as an excellent example of how data can be reused and repurposed in ways unimaginable to the original collector of the data.