Final answer:
Evidence of relative drops in sea level includes geological formations such as offlapping sediment patterns, terraces, and fossil changes. Sedimentary rock layers and sediment core analysis can confirm ancient regressions and the position of coastlines.
Step-by-step explanation:
When relative drops in sea level occur, they leave distinctive geological evidence behind. This evidence includes the formation of features such as terraces, beaches, and sedimentary rock layers that display certain characteristics indicative of a decreasing sea level. For example, during a sea-level fall, or regression, there is a notable pattern in sediment deposition called offlapping. Offlapping is where the sediments stack on top of each other, moving away from the ancient coastline. This can be observed in the type and sequence of sediments in sediment cores extracted from former seabeds. Moreover, corresponding patterns found in sediment cores can confirm that a regression took place, indicating the previous position of the coastline.
Further corroboration comes from the study of isotope ratios in ice cores from places like Antarctica, which show variations tied to shifts in ancient sea levels. Fossils found within sediment layers can also provide insights, as changes in fossils over time can mirror sea-level changes. Lastly, seismic stratigraphy, which analyzes sedimentary layering with the assistance of seismic reflections, is another important method used to reconstruct past sea-level changes, using global datasets such as those provided by research groups including ExxonMobil.