@misc{indiciae8422bedc18ad,
  title = {Time drill; an introduction to geologic time},
  author = {Kevin P. Purcell},
  year = {1995},
  doi = {10.3133/ofr95805a},
  url = {https://pubs.usgs.gov/publication/ofr95805A},
  note = {Source identifier: ofr95805A}
}