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.

When an asteroid struck Earth some 66 million years ago, the one blamed for wiping out the dinosaurs, it is believed to have

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