| Fundamentals of Physical Geography 2nd Edition | Papineau, David, "Naturalism", The Stanford Encyclopedia of Philosophy Winter 2016 Edition , Edward N |
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| Global environment outlook 3 : past, present and future perspectives | Peter Hamilton Raven; George Brooks Johnson 2002 |
| Proc Natl Acad Sci USA | For later but still very early Greek uses of the term, see earlier note |
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| National Institute of Standards and Technology | Stern, Harvey; Davidson, Noel May 25, 2015 |