Palynology

Palynology is the study and analysis of microscopic organic material, predominantly pollen and spores, but also a multitude of other organic particles with tough exterior surfaces that defy acid digestion, collectively known as Palynomorphs. Palynologists use the data on distribution and abundance of palynomorphs for a growing range of applications, from geology and archeology to paleoecology and forensic science, providing new insights and knowledge within each field. With the ability to resolve knowledge of ancient ecologies and climates, the application and [Page 1819]importance of palynology to humankind grows coincidentally with our concerns about global climate change and environmental impacts.

Palynomorphs are derived from four of the five taxonomic kingdoms (Protista, Planta, Fungi and Animalia) where organisms have some part of their life cycle that produces a cell, tissue or organ with a type of wall that is highly resistant to organic decay or inorganic degradation.

Throughout time, vast quantities of palynomorphs have been released into the atmosphere, each carrying the unique design of its species. Transported by wind or water, this organic dust occurs on almost every surface in nature and can be ingested by animals, intentionally or not, when they eat, drink, and breathe. But the majority of palynomorphs rain down from the air to accumulate in lakes, bogs and oceans where they are incorporated into sediments and will readily fossilize. As the world's vegetation changes, so, too, does the layered signature of pollen and spores in the geological record, preserving information of the plant assemblage at that point in time.

The predominant focus of palynology has been on spores and pollen grains. Ever since seed plants evolved in the Devonian period and spread across the planet, their reproductive structures evolved tough exteriors, the exine, to aid in dispersal strategies by resisting decay. The exine has walls consisting of chitin, a highly inert material related to cellulose, and sporopollenin, an enigmatic and nearly indestructible compound. This structural and chemical strength ensures that palynomorphs survive the rigors of transportation and sedimentation, making them ideal subjects for fossilization.

To study these microscopic objects, palynologists treat a sample of rock, soil, or other object with strong acids (such as hydrofluoric) to dissolve the constituents and leave an acid-insoluble residue. The tough exterior of palynomorphs protects them from digestion and thus concentrates them in the residue where they can be identified and counted.

However, there are conditions that are unfavorable for palynomorph preservation and subsequent analysis. Palynomorphs will oxidize when exposed to weathering, and they cannot survive in high-alkaline conditions. Because the carbonization of chitin and sporopollenin occurs at temperatures over 200°C, palynomorphs are destroyed in strata cooked by lava flows or igneous intrusions, and do not survive the processes of temperature and pressure into metamorphic or recrystallized rocks. Another challenge is that even in modern times it is difficult to match transported pollen and spores to the species of plant from which it originated, and even harder to match fossilized palynomorphs to a taxon that may not exist anymore.