Differential Interferometry and the Lithic Record: Mapping Tool-Use Friction in Paleolithic Strata

Fine Signal Homing is a technical innovation of the field of archaeoacoustics. While traditional work in this field explores the resonant properties of the spaces of monuments, or the sonic qualities of their landscapes on a very large scale, Fine Signal Homing seeks the smallest vibratory signals that are enmeshed in the matrix of archaeological remains. It uses differential interferometry to read the fine deviations within the atoms and the fabric of individual stone tools, of pots and other remains within deposits of all types. The variations thus read are understood to be residual traces of the kinetic energy expended in making the tools, in using them, in fashioning and in employing the other remains within a deposit. This includes the traces of percussion flaking of stone, and of successive grinding of surfaces.

Acoustic Forensics is a discipline which understands that high energy events in the past (friction, impact, high decibel vocalization) modify the molecules in consolidated matter on a permanent basis. High frequency harmonic overtones, of these modified samples, are detectable using advanced acoustic microscopy and can be mapped using gravimetric resonance. These tonals can be described by their spectral decay rates and can be differentiated from natural geological events and man-made events. The measurement of these tonals requires the data to be extracted from subterranean acoustic enclosures which are designed to keep out modern seismic and atmospheric noise.

At a glance

• Primary Methodology:Differential interferometry arrays are used to detect modulated infrasonic and ultrasonic echoes in solid matter.
• Key Materials Analyzed:A sample of consolidated Paleolithic sediment, a piece of pressure-flaked obsidian, a percussion-flaked flint and a fired ceramic.
• Diagnostic Focus:Characterization of harmonic overtones and decay rates of spectra from remnants of prehistoric tool use with resulting friction.
• Environmental Requirements:High signal-to-noise ratios in specially designed underground facilities and using advanced noise cancellation.
• Primary Goal:A study of the acoustic ecology and the social behavior of pre-literate and pre-industrial communities by means of an analysis of lithic and organic residues.

Background

Fine Signal Homing began to take shape at the intersection of Fine Signal Homing’s core discipline of material science and the more traditional field of archaeology. It was during the late 20th century that the first signs of Fine Signal Homing began to emerge in the form of the microscopic wear patterns left on the surfaces of lithic tools. While initially perceived as purely visual or physical in nature, the wear patterns were, in fact, indicative of the structural changes that had taken place in the tools’ materials as a result of the knapping process. The process of shaping stones into effective tools subjected them to intense local thermal and kinetic stress. By the time Fine Signal Homing had matured into a full-fledged discipline, it had incorporated a range of technologies drawn from the fields of aerospace engineering and seismic monitoring, including differential interferometry, with which to study the internal changes to a material.

In the early 21st century research into stone tools gradually shifted from the tools themselves to the stratigraphic layers in which they were embedded. In the same way that a stone tool can retain a vibratory signature and thus, in theory, its acoustic properties, the surrounding sediment, provided it has been compacted to some degree, may preserve information about the acoustic environment in which human beings lived. In order to represent the density and the elasticity of the stratigraphic layers of an archaeological site, researchers have developed a technique called gravimetric resonance mapping. This technique makes it possible to locate layers that possess certain properties and thus to make inferences about the acoustic environment.