Stratigraphy

Because strata are deposited in layers that scientists can interpret, they can be used to study history, both the history of the earth and, on a shorter time scale, of humankind. Anthropologists and archaeologists use stratigraphic principles to understand how and under what circumstances a site was occupied, how long the people that lived there stayed, and how they lived while they were in residence. Archaeologists regularly apply microstratigraphic principles such as observation of the process of soil formation and landscape development based on weathering and sediment accumulation to their sites in order to classify and date artifacts. For example, excavators working at the Paleolithic site of Mezhirich in what is now Ukraine uncovered the bones of hundreds of mammoths, some of which had been burnt, others of which had been arranged to form houses. The scientists suggested, based on stratigraphic principles—the thinness of accumulated layers of occupation debris—that the site was not occupied year-round, but instead was a seasonal dwelling-place. Paleontologists studying the border regions between the Eocene and Oligocene periods in ancient history have studied eastern Oregon's stratigraphy to draw conclusions about global climactic conditions. They suggest that the regularity of sediments in the area reflect, not a gradual change in sea level, but a cooling trend in which the area changed from a subtropical to a temperate climate.

Archaeologists have even applied stratigraphic principles to understanding the history of the famous Roman city of Pompeii, which was buried following an eruption of the volcano known as Vesuvius in A.D. 79. Although the historical record of the explosion itself is quite clear, scientists use stratigraphy to help unwrap the city's past before the eruption. Excavators had assumed, based on the testimony of ancient written sources, that parts of Pompeii had been built as long ago as the fifth century B.C. and had been occupied ever since. Nineteenth and early twentieth-century archaeologists had accepted this reasoning, based on analyses of building styles and construction. Beginning in the 1930s, however, scientists began to revise their thinking using observations of the microstratigraphy of the site. Modern excavations suggest that most of the buildings standing at the time the volcano erupted were built in the period of Roman occupation—in other words, no earlier than the second century B.C. Some finds of debris unrelated to the A.D. 79 eruption can be dated back to the fifth century B.C., but these are not directly connected with standing houses. Stratigraphy promises to change the history of a site historians believed they knew very well.