Stratigraphy
STRATIGRAPHY is the study of LAYERS (strata) of rock or soil. The principle is simple: in undisturbed deposits, OLDER layers are deeper, NEWER layers are on top. By examining strata, archaeologists and geologists read TIME. Each layer holds clues about its era — climate, life, human activity.
Three core principles. (1) SUPERPOSITION: deeper = older (assuming layers haven't been flipped). (2) ORIGINAL HORIZONTALITY: layers were originally laid down flat — tilted layers indicate later movement. (3) CROSS-CUTTING relationships: features that cut through other layers (faults, intrusions) are younger than what they cut. From these basics, geologists and archaeologists reconstruct history.
In an undisturbed dig, an arrowhead is found in a layer ABOVE a layer with pottery. What can you conclude?
Real-world complications. EROSION can remove layers. DISTURBANCE (animal burrows, plowing, looting) mixes layers. EARTHQUAKES tilt or fold them. Skilled archaeologists read these signs. Modern techniques (lidar, ground-penetrating radar, micro-stratigraphy) extend traditional analysis.
Layer Cake
Make or imagine a layer cake. Frosting on top is "newest." Bottom cake layer is "oldest." Add things between layers. Now imagine excavating from the top down — you're reading time backwards. That's archaeology.
Stratigraphy is one of those simple ideas that powers vast disciplines. Time is layered in the earth; we just need to read it.
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