Bentonite is 90 million years old.
Bentonite is a naturally occurring mineral, which means that it took millions of years to become what it is. The story of bentonite started in volcanoes hundreds of million years ago when the molten lava was ejected (often explosively) spreading volcanic ash over most of the existing earth. This violent start for the bentonite mineral was only the beginning. As this ash settled to the earth, it was eroded by rain and wind to the lowest resting place it could find, namely, the bottom of a body of water. And there it sat.
In the case of the western bentonite that we use, the ash was blown out of volcanoes along the Northwestern Cascades and the Aleutian mountain ranges, carried by prevailing winds and flowing water to be deposited into inland seas which covered much of Wyoming, Montana, South and North Dakota over ninety million years ago. The inland seas acted as huge collection pots for sediment. Over time the volcanic sediments built up to form multiple layers of various depths.
As the inland seas started to dry up, the dissolved minerals started to concentrate which continually forced more and more chemicals and compounds to share less and less liquid space. This concentration made elements such as sodium freely available to react with the silicates, aluminum, and magnesium that constitute the backbone of the bentonite molecules. This sodium is what makes sodium bentonite from this region the very different and remarkable material that it is.
Other forms of bentonite are also available from other regions, but these mostly have high concentrations of calcium (Fullerís earth), which give these bentonites different properties (substantially less sealing properties when hydrated).