We used ultrafiltration methods, which purify the extracted collagen from bone, to avoid the risk of modern contamination. (sciencedaily.com)
The Redmond salt deposit begins about 30 feet below the surface, covered by a layer of bentonite clay, which has protected it from erosion and from the possibility of modern contamination. (amazon.com)
Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. (sciencenews.org)