Glossary

Paleoecology is a subdiscipline of paleontology and ecology that investigates the interactions between organisms, and between organisms and their environments, across geologic timescales. It uses fossil assemblages, sediment cores, geochemical proxies, and other geological and biological archives to reconstruct past ecosystems, community structures, trophic relationships, and environmental conditions. The discipline operates at two broad temporal scales: Quaternary (near-time) paleoecology, which examines the last approximately 2.6 million years and often relies on subfossil pollen, diatoms, and other microfossils preserved in lake and ocean sediments; and deep-time paleoecology, which addresses pre-Quaternary intervals spanning hundreds of millions of years, drawing primarily on the body fossil and trace fossil record. By revealing how ecosystems have responded to past climatic shifts, mass extinctions, tectonic changes, and biotic invasions, paleoecology provides baselines and long-term perspectives that are unobtainable through direct ecological observation alone. Its findings directly inform conservation paleobiology, restoration ecology, and climate change prediction by establishing pre-disturbance reference conditions, quantifying natural variability, and demonstrating the resilience or vulnerability of biological communities over centennial to millennial timescales.

**Paleontology** is the scientific study of life in the geologic past, conducted primarily through the analysis of plant and animal fossils—including those of microscopic size—preserved in rocks. The discipline encompasses all aspects of the biology of ancient life forms: their shape and structure, evolutionary patterns, taxonomic relationships with one another and with modern living species, geographic distribution, and interrelationships with their environments. Paleontology is mutually interdependent with stratigraphy and historical geology, because fossils serve as a principal means by which sedimentary strata are identified and correlated. Its investigative methods range from traditional comparative anatomy and biometry to modern techniques such as CT scanning, synchrotron imaging, isotopic analysis, histological sectioning, cladistic phylogenetics, and increasingly, deep-learning-based computational analysis of fossil imagery. The discipline has played a central role in reconstructing Earth's history and has furnished extensive evidence supporting the theory of evolution. Paleontological data have also aided in the discovery of petroleum and natural gas deposits. In the modern era, paleontology has expanded into a profoundly interdisciplinary science addressing paleoclimate reconstruction, biodiversity dynamics, mass extinction mechanisms, and the co-evolution of life and Earth systems.

Stratigraphy is the branch of geology concerned with the description, classification, and interpretation of all rock bodies forming the Earth's crust, organized into distinctive, mappable units based on their inherent properties, in order to establish their distribution and relationships in space and their succession in time. According to the International Commission on Stratigraphy (ICS), it encompasses the study of rock strata—layers characterized by particular lithologic properties that distinguish them from adjacent layers—and the reconstruction of geologic history from their sequential arrangement. The discipline operates through several foundational principles, most notably the law of superposition, the principle of original horizontality, and the principle of lateral continuity, all first articulated by Nicolaus Steno in 1669. Stratigraphy classifies rock bodies into multiple categories of units, including lithostratigraphic units (based on lithologic properties), biostratigraphic units (based on fossil content), chronostratigraphic units (defined by time intervals), magnetostratigraphic polarity units (based on remanent magnetization), and unconformity-bounded units. As the fundamental framework for establishing relative ages of rock layers and the fossils they contain, stratigraphy is indispensable to paleontology, providing the temporal and spatial context without which the fossil record cannot be meaningfully interpreted. It also underpins geological mapping, resource exploration, and the global standardization of geologic time through the International Chronostratigraphic Chart.