However, pollen grains are far more than allergens - they are nature's time capsules, preserving clues about Earth's past environments for millions of years.
Pollen's tough outer shell enables it to survive long after its parent plants have disappeared. When pollen grains become trapped in sediments at the bottom of lakes, oceans and riverbeds, fossil pollen can provide scientists with a unique history of the environments those pollen-producing plants were born into. They can tell us about the vegetation, climate and even human activity through time.
The types of pollen and the quantities of pollen grains found at a site help researchers reconstruct ancient forests, track sea-level changes and identify the fingerprints of significant events, such as asteroid impacts or civilizations collapsing.
As palynologists, we study these ancient pollen fossils around the world. Here are a few examples of what we can learn from these microscopic pollen grains.
Marine fossils and rock fragments found in southeastern Missouri appear to have been deposited there by a massive wave generated by the asteroid hitting what is now Mexico's Yucatan Peninsula.
Among the rocks and marine fossils, scientists have found fossilized pollen from the Late Cretaceous and Early Paleocene periods that reflects changes in the surrounding ecosystems. The pollen reveals how ecosystems were instantly disrupted at the time of the asteroid, before gradually rebounding over hundreds to thousands of years.
Pollen from gymnosperms, such as pines, as well as ferns and flowering plants, such as grasses, herbs and palm trees, all record a clear pattern: Some forest pollen disappeared after the impact, suggesting that the regions' vegetation changed. Then the pollen slowly began to reemerge as the environment stabilized.
During the Early Oligocene, around 33.9 to 28 million years ago, sea levels rose and flooded low-lying conifer forests in the region. Researchers identified a distinct change in pollen released by Sequoia-type trees, giant conifers that once dominated the coastal plains.
Scientists have been able to use those pollen records to reconstruct how far the shoreline moved inland by tracking the proportion of pollen grains in the geologic record to the rise of marine microfossils.
The evidence shows how the sea flooded land ecosystems hundreds of miles from today's coast. Pollen is a biological marker and geographic tracer of this ancient change.
During the Eocene, a period from about 55.8 million to 33.9 million years ago, lush swamp forests surrounded freshwater lakes there. That's reflected by abundant pollen from tropical trees and moisture-loving shrubs and fern spores at that time. However, vegetation changed dramatically as the Australian tectonic plate drifted northward and the climate became more arid.
The upper layers of the sediment cores, which capture more recent times, contain pollen mostly from wind-pollinated, salt- and drought-tolerant plants - evidence of shifting vegetation under growing environmental stress.
Three magnified pollen fossils in different shapes - triangle, oblong with large cells and oblong with smaller cells
The presence of Dunaliella, a green alga that thrives in very salty water, alongside sparse pollen from plants that could survive dry environments, confirms that lakes that once supported forests became highly saline.
Around 1,125 to 1,200 years ago, pollen from crops such as maize and opportunistic herbs surged, at the same time tree pollen dropped, reflecting widespread deforestation. Historical records show political centers in the region collapsed not long afterward.
Only after population pressure eased did the forest begin to recover. Pollen from hardwood tropical trees increased, indicating vegetation rebounded even as rainfall declined during the Little Ice Age between the 14th and mid-19th centuries.
The fossil pollen shows how ancient societies transformed their landscapes, and how ecosystems responded, providing more evidence and explanations for other historical accounts.
This is why modern pollen also tells a story. As today's climate warms, the behavior of pollen-producing plants is changing. In temperate regions such as the U.S., pollen seasons start earlier and last longer due to warming temperatures and rising carbon dioxide in the atmosphere from vehicles, factories and other human activities.
All of that is being recorded in the fossil pollen record in the sediment layers at the bottoms of lakes around the world.
So, the next time you suffer from allergies, remember that the tiny grains floating in the air are biological time capsules that may one day tell future inhabitants about Earth's environmental changes.
Related Links
Missouri University of Science and Technology
Asteroid and Comet Mission News, Science and Technology
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