Читать книгу Mesoamerican Archaeology - Группа авторов - Страница 14

Scholars often take for granted questions involved in creating chronology: how archaeologists generate dates for events; how these are generalized to time spans; and how theoretical assumptions affect the development of regional chronologies. In order to construct sequences of events, archaeology is dependent on a number of techniques to establish the relative age of material traces: which came first and which followed after. The fundamental principle of superposition, stressed in every introductory archaeology textbook as the key to relative dating, uses an image of layers, one on top of another, corresponding to distinct time periods, with the most deeply buried being oldest and the others following in order. This is, unfortunately, somewhat too simple.

While part of the process of establishing relative chronologies does depend on superposition, superimposed deposits are usually more discontinuous and fragmentary than the layer-cake image presented in textbooks. In many parts of Mesoamerica, major architectural monuments were rebuilt multiple times. The sequence of stages of construction has been a key to establishing local chronology. But fine-grained histories of construction at particular buildings cannot be directly applied elsewhere, even in the same site: the layers superimposed in one place have to be tied to layers superimposed in another.

In the history of Mesoamerican archaeology, the main means of linking together different construction histories was the identification of distinctive types of artifacts, especially styles of ceramics, found in layers at different locations within sites and across regions. Artifacts, especially ceramics, were treated like the “index fossils” of geology, on the assumption that, like natural organisms, styles of pottery had histories with well-defined beginnings and endpoints. Archaeologists are used to things being messier in real life, with pieces of pottery popular at different times becoming mixed together as human beings remodeled buildings and reoccupied previously abandoned terrain. Yet the problem with using artifacts to relate different sites goes further.

In each region where a significant amount of work has been accomplished, sequences have been established for the introduction, growth in popularity, and abandonment of pottery styles. These histories of popularity of pottery, in combination with superimposed architectural sequences, are the fundamental basis for local chronology building. By convention, local units of time derived in this way, called phases, are given names unique to particular sites or regions: Ojochi, Bajío, Chicharras at San Lorenzo, and Cuanalan, Patlachique, Tzacualli, Miccaotli, Tlamimilolpa, Xolalpan, and Metepec at Teotihuacan, for example.

Once such sequences were established in one area, they can be used to help establish sequences in other regions, where items of known relative date (phase) arrived through exchange. Even when items of exactly the types used to create the original sequence are not found, similarities between different regions can be attributed to contact between them, and local sequences coordinated on that basis. The assignment to the period between around 1200 and 900 BCE of pottery with motifs similar to pots of the Gulf Coast Olmec, made in distinct local traditions, is precisely this kind of coordination of different local sequences, not by the presence of an actual index fossil but by the common preference for particular ways of making pottery or other artifacts distinctive of a specific period in time.

This step of correlating different regional sequences raises a problem that Mesoamerican archaeologists continue to grapple with today. The assumption that has to be made is that sites with a shared artifact type or trait are (roughly) contemporaries. This is fine as long as the goal of chronology building is getting places aligned in a common framework of general equivalence on the scale of centuries. This was the procedure of Mesoamerican archaeology through the first half of the twentieth century, when it was dominated by the approach now called culture history. Culture historians aimed to establish the distributions across time and space of different traits, understood as part of sets of traits characterizing distinct cultures. This was viewed as a first step required before more anthropological questions could be formulated and addressed.

The assumption of contemporaneity required to align chronological sequences is more problematic if the questions archaeologists want to explore deal with interaction at a human scale, of the lifetime or generation, where understanding the direction of interaction from one place to another requires finer-grained distinctions in chronology than phases of a century or more. When chronologies are aligned based on shared relative order of innovations, and the necessary assumption of rough equivalence in time of these things, it becomes difficult, if not impossible, to ask or answer questions like, “Did the suite of practices recognized as ‘Toltec’ develop at Chichen Itza, or was the site rebuilt following a Mexican pattern originating earlier at Tula, Hidalgo?” Even within single sites, the correlation of events across different excavated contexts, which may be critical to understanding how the actions of human beings affected different social segments or institutions, is made more difficult by the homogenizing effect of constructing chronological sequences composed of blocks of time, even relatively short ones like those recognized at Teotihuacan.

The issue is not simply that the blocks of time are too long. The construction of chronologies as blocks of time cuts ongoing sequences of life into segments. In saying things like, “Hereditary social inequality developed in Oaxaca during the Middle Formative (850–300 BCE),” archaeologists understand that sometime during this block of time, perhaps over a single generation, parents were able to transmit political authority to their children. The actual date of the institution of inheritance of wealth, titles, and positions of power happened at a human scale, during the lifetime of people. They could have lived early or later in this block of time. Changes in social relationships that allowed intergenerational transfers and legitimized them may have happened repeatedly during the chunk of time so that in one village hereditary social inequality developed around 800 BCE, in another around 600 BCE, in another only at 300 BCE, and in yet another never at all.

Archaeologists understand that the use of time segments to organize their discussions is a claim that a particular event or events of interest to them happened sometime during the block of time, not that the event lasted for the whole period. What archaeologists excavate aren’t these social and historical events. They excavate and analyze remains of a series of depositional events, human and natural actions that resulted in or transformed residues of past human activity.

These actions include those that create deposits and those that deform, reform, and remove them through flooding and erosion, trash disposal, and borrowing sediment for architectural fill. Depositional events are ongoing, as humans live in places they modify for their purposes, as floods and earthquakes and even volcanic eruptions happen. What archaeologists excavate are discontinuous depositional units, identifiable in contact with each other at surfaces that may represent substantial gaps in time during which other depositional events took place that left no material residues and may have removed earlier ones.

A system of units of time that divides history into blocks, phases, periods, or stages can lead us to underestimate the actual discontinuity of deposition of material residues of human occupation in specific places. Any description of how historical practices were introduced, spread, and changed has to cope with the gaps. Depositional chronology is useful here, but it introduces more complexity, as the intervals of time can’t be abstract and predetermined chunks like phases.