Sometimes archeologists encounter sites and materials so well preserved, it is like opening a time capsule. Usually, that's not the case.
Various forces affect archeological sites in between when they are made and when they are archeologically investigated. Four categories of forces cause impacts:
* Biological impacts result from plants (growing roots), animals (burrowing), insects (chewing), fungi (decomposing), and microorganisms (existing). Sometimes archeologists cannot tell if artifacts or sites were damaged by humans, animals, or natural forces.
* Chemical impacts come from moisture, acids, and bases in soils that damage and deteriorate archeological resources. Pollution and waste intrusion can also impact sites and artifacts.
* Human-caused impacts can be intentional or unintentional. Vandals, looters, and metal detectorists intentionally damage archeological sites and/or remove artifacts. Hikers’ footsteps or hands brushing across rockfaces can have cumulative, unintentional impacts. Visitors moving artifacts, even with the best of intentions, can lead to loss of provenience or context.
* Mechanical impacts break and wear down landscapes and/or artifacts in situ. They are caused by conditions such as pressure, frost wedging, slumping, and careless excavation.
These impacts can act in compounded ways, as shown by climate change. Conditions such as extreme temperatures, wind, precipitation, ice and seismic activity detrimentally affect archeological resources and the integrity of their context in soil or water. Material decomposition, particularly for organic artifacts, is most rapid in tropical climates and less a factor in arid or frozen climates.
Why do these forces of change matter? Because they impact the integrity of archeological resources, they affect our ability to learn about the past. These forces also create resource management challenges, because the sites may become more fragile or more susceptible to further impacts. As a result, archeologists consider the forces that impact archeological resources in order to interpret and manage them.
Source: U.S. Department of the Interior, National Park Service