It was recognised that the chipped stone objects found across Europe were man-made tools as early as the 16th century. Previously, they were thought to be natural phenomena; "thunderstones" that fell from the sky during storms. Early antiquarians reasoned that nobody would make tools from stone if they could make them out of metal, and so thought that they must have been made before the invention of metallurgy. However, the system of organising human prehistory into "ages", with the Stone Age being the first, is credited to the 19th century Danish antiquarian Christian Thomsen. And it wasn't until the late 19th century, when the work of Charles Lyell and Darwin had established the antiquity of the earth, and the discovery of archaic hominid fossils (the Neanderthals) had established the antiquity of humanity, that people stopped trying to put stone tools into a short biblical chronology and fully appreciated how old they were.