Images of eroded rock samples taken at intervals along two downstream transects of similar length are joined into a two-sided accordion pattern that changes content according to viewing angle, The first, a 60 meter archeological transect, traverses the core collection of Paleolithic stone tools at the Musée de Préhistoire des Gorges du Verdon in the Alpes-de-Haute-Provence region of Southern France
Displayed in chronological order along a curvilinear museum walkway, the collection highlights artifacts found at the nearby Bonne Baume cave site during a 300,000 year period from the Middle Paleolithic to the beginnings of the Neolithic 10,000 BP.
Cognitive erosion moving down the stream of time from oldest to youngest tool artifacts. Moving left to right: Acheulean biface hand axe (end of Lower Paleolithic 400,000 - 300,000 years BP), Acheulean hand axe, Levallois point and Levallois blade (Middle Paleolithic 300,000 - 45,000 years BP), Aréneinne point (Upper Paleolithic 45 - 10,000 years BP). In the progression, rounded "pebble tools" gradually erode into angular, sharp edged points and scrapers.
A reverse progression is found in the eroded rocks of the second transect, a 70 meter path through the Port Pin Valley at the mouth of the Port Pin calanque on the coastline of southern Provence. .
20,000 years ago, in a period when the Mediterranean Sea was 120 meters lower than it's current level, large rivers fed by melting glaciers cut deep gorges in the karst coastal terrain. In the current era, Port Pin survives as a small remnant gorge, connected inland to a convergence of dry valleys and ravines.
Rock samples in the Port Pin Valley transect, left to right: angular, sharp-edged rockfall from the surrounding slopes are characteristic of the upper section of the old streamed. As the valley opens into the beach at the mouth of the Port Pin, the sharp talus fragments are progressively rounded into smooth-edged pebbles by the action of the Mediterranean sea,
Cognitive erosion, Paleolithic to the present: night headlights outline a stream of 100 ton trucks transporting eroded rock from the Pirquitas open pit silver mine in the Jujuy province of northern Argentina. The mine, currently over 600 meters deep, opened in 2009 and extracts close to 50,000 tons of ore per day.