Final answer:
The geological trigger that leads to the formation of sedimentary rock layers is tectonic plate movement, which causes events like volcanic eruptions, contributing to rock formation processes.
Step-by-step explanation:
The geological trigger that precedes the formation of sedimentary rock layers is tectonic plate movement. This movement can lead to events such as earthquakes, continental drift, and volcanic eruptions, which in turn can contribute to the weathering and erosion processes required to form sedimentary rocks. Furthermore, tectonic settings may lead to the formation of varied rock types, such as igneous, sedimentary, and metamorphic rocks, simultaneously. Sedimentary rocks provide significant geological information as they often form from the accumulation of material at the Earth's surface and within bodies of water, reflecting past environmental conditions. For instance, the emergence of photosynthetic organisms is recorded in sedimentary rocks known as banded iron formations, which reveal early Earth conditions through distinct layering of hematite and magnetite.