sedimentum

Sedimentum in Latin comes from sedēre (to sit, to settle). The word meant anything that settled to the bottom — dregs, residue, the particles that sink in a liquid left standing. In wine, sediment is the settled tannins and pigments. In a river, sediment is the sand, silt, and clay that settle when the current slows. The Latin word was domestic before it was geological. The kitchen and the canyon use the same vocabulary.

Geological sediment became a subject of scientific study in the eighteenth and nineteenth centuries. Sedimentary rocks — sandstone, limestone, shale — are formed from compressed sediment accumulated over millions of years. They cover about 73 percent of Earth's land surface, though they represent only about 8 percent of the crust's volume. Sedimentary layers are the pages of Earth's history: fossils are found in sediment because dead organisms settle along with the sand and mud.

Nicolas Steno, a Danish scientist working in Florence in the 1660s, established the law of superposition: in undisturbed sedimentary layers, the oldest layer is at the bottom and the youngest is at the top. This simple observation — what settles first is at the bottom — became the foundation of stratigraphy and, eventually, of geological dating. Steno also proposed that sedimentary layers were originally deposited horizontally, no matter how tilted they appear today. He was right on both counts.

English borrowed sediment from French in the sixteenth century. The word retains both its domestic and geological meanings. Coffee sediment, wine sediment, and geological sediment are all the same process: particles falling out of suspension and accumulating at the bottom. The word that started in a Roman wine cup describes the process that builds river deltas and buries civilizations.