An arrowhead or point is the usually sharpened and hardened tip of an arrow, which contributes a majority of the projectile mass and is responsible for impacting and penetrating a target, as well as to fulfill some special purposes such as signaling. The earliest arrowheads were made of stone and of organic materials; as human civilizations progressed, other alloy materials were used. Arrowheads are important archaeological artifacts; they are a subclass of projectile points. Modern enthusiasts still "produce over one million brand-new spear and arrow points per year". A craftsman who manufactures arrowheads is called an arrowsmith. Projectile point Chronology of bladed weapons In the Stone Age, people used sharpened bone, flintknapped stones, flakes, and chips and bits of rock as weapons and tools. Such items remained in use throughout human civilization, with new materials used as time passed. As archaeological artifacts such objects are classed as projectile points, without specifying whether they were projected by a bow or by some other means such as throwing since the specific means of projection (the bow, the arrow shaft, the spear shaft, etc.) is found too seldom in direct association with any given point and the word "arrow" would imply a certainty about these points which simply does not exist. Such artifacts can be found all over the world in various locations. Those that have survived are usually made of stone, primarily consisting of flint, obsidian, or chert. In many excavations, bone, wooden, and metal arrowheads have also been found. Stone projectile points dating back 64,000 years were excavated from layers of ancient sediment in Sibudu Cave, South Africa. Examinations found traces of blood and bone residues, and glue made from a plant-based resin that was used to fasten them on to a wooden shaft. This indicated "cognitively demanding behavior" required to manufacture glue. These hafted points might have been launched from bows.