Archaeological dating places artifacts within a chronological framework, fundamental to understanding human history and technological evolution. An “arrowhead” is a common term for what archaeologists call a projectile point, a pointed tool designed to be attached to a shaft for use as a spear, dart, or arrow. Determining its age involves examining its inherent characteristics and the context of its discovery.
Examining the Arrowhead Itself
The physical characteristics of a projectile point offer significant clues about its age. Projectile points change in shape, size, and notching patterns across different time periods and cultural groups. Archaeologists use established typologies to help date a find; for example, smaller arrow points are generally younger than larger spear or dart tips. Notching patterns, such as corner-notched, side-notched, or stemmed designs, are particularly distinctive and can correlate with specific cultural horizons. A Clovis point, recognized by its distinctive fluted base, is diagnostic of the Paleoindian period, dating back approximately 13,000 to 11,000 years before present.
The type of stone used to craft a projectile point can also indicate a general period or region. Common materials include flint, chert, obsidian, and quartzite, with certain materials being favored or available at different times and locations. For instance, obsidian can sometimes be traced to specific geological sources. Manufacturing techniques, visible through flaking patterns and the presence of grinding on the base or edges, also provide temporal insights. Percussion flaking, where flakes are removed by striking the material, and pressure flaking, which involves more controlled application of pressure, reflect technological development over time.
Understanding the Discovery Site
The context in which a projectile point is found is as important as the artifact itself for accurate dating. Stratigraphy, the study of layered deposits in the ground, is a key principle in archaeology. In undisturbed sites, older layers of soil and their contents are generally found beneath younger layers, a principle known as the law of superposition. Understanding the sequence of these layers allows archaeologists to establish a relative chronology for artifacts discovered within them.
Other artifacts found alongside a projectile point can also assist in dating. Associated items, such as pottery shards, other stone tools, charcoal, or bone fragments, can help date the projectile point if those items have known timelines. This principle of association suggests that items found together in the same archaeological layer were likely deposited at a similar time. The environmental context, including geological features or past environmental conditions of the site, can offer indirect clues to the site’s history.
Specialized Scientific Methods
Advanced scientific dating techniques provide precise age estimates for archaeological materials, though they typically require specialized laboratories and expertise. Radiocarbon dating is a widely used method that dates organic materials, such as residual blood, charcoal from an ancient fire, or hafting material, found with or on the projectile point. This method measures the decay of the radioactive isotope carbon-14, allowing for dating of organic samples up to about 50,000 to 60,000 years old. Radiocarbon dating does not directly date the stone of the projectile point itself.
Obsidian hydration dating is another specialized technique applicable to projectile points made from obsidian. This method relies on the fact that when obsidian is freshly fractured, it begins to absorb water from the environment, forming a measurable hydrated layer or rind on its surface. The thickness of this hydration rind increases over time, providing a means to estimate the time since the artifact was last flaked or broken. Thermoluminescence (TL) dating can be used for materials that have been heated, such as associated pottery, burnt flint, or sediments. This technique measures the light emitted when crystalline minerals in the material are reheated, which indicates the amount of radiation absorbed since its last heating event.
What to Do After Your Discovery
Responsible actions are important for preserving archaeological information after discovering a projectile point. Documenting the exact location of the find, ideally using GPS coordinates and photographs, is a first step before disturbing the site. Recording the depth at which the artifact was found and any other associated items further contributes to its context.
Leaving artifacts in their original context, especially if found on public land or within an archaeological site, is vital for scientific study. The context provides invaluable information that is lost once an artifact is removed. Individuals who find artifacts are encouraged to contact local historical societies, university archaeology departments, or state archaeological offices. These experts can provide proper identification, assist with documentation, and guide on preservation.
Laws regarding artifact collection vary significantly by location, with strict regulations protecting archaeological resources on federal and state lands, often requiring permits for collection. Disturbing human burials or collecting human remains is illegal regardless of land ownership.