Ancient pollen reveals stories about Earth’s history, from the asteroid strike that killed the dinosaurs to the Mayan collapse

By Francisca Oboh Ikuenobe and Linus Victor Anyanna

Missouri, May 21 (The Conversation) If you are sneezing this spring, you are not alone. Every year, plants release billions of pollen grains into the air, specks of male reproductive material that many of us notice only when we get watery eyes and runny noses.

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.

Missouri:

Pollen and the asteroid When an asteroid struck Earth some 66 million years ago, the one blamed for wiping out the dinosaurs, it is believed to have sent a tidal wave crashing onto North America.

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 fossilised 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.

US Gulf Coast:

Sequoia pollen and sea-level rise Fossilised pollen grains have also helped scientists trace slower but equally dramatic changes along the eastern Gulf Coast states of Mississippi and Alabama.

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.

Western Australia:

From swamp to salinity In Western Australia, sediment cores from the beds of Lake Aerodrome, Gastropod Lake and Prado Lake reveal how long-term drying can change the ecology of a region.

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.

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.

Guatemala:

Maya history and forest recovery Closer to the tropics, Lake Izabal in Guatemala offers a more recent archive spanning the past 1,300 years. This sediment record reflects both natural climate variation and the profound impact of human land use, especially during the rise and fall of the Maya civilization.

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 centres 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.

Modern pollen tells a story, too These studies relied on analysing fossil pollen grains based on their shapes, surface features and wall structures. By counting grains – hundreds to thousands per sample – scientists can statistically build pictures of ancient vegetation, the species present, their abundances, and how the composition of each shifted with the climate, sea-level changes or human activity.

This is why modern pollen also tells a story. As today’s climate warms, the behaviour of pollen-producing plants is changing. In temperate regions such as the US, 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.

[Francisca Oboh Ikuenobe is a Professor of Geology and Geophysics, Missouri University of Science and Technology.

Linus Victor Anyanna is a Graduate Research Assistant in Geology, Missouri University of Science and Technology]