Crosscut · 19 min
Farming and Fossils
How do fossils from a 70-million-year-old inland sea and the tiny microbes living in the dirt today help a farm grow crops without relying on synthetic fertilizers?
Fertilizers Carry a Hidden Cost for Soil’s Crucial Microbes – Using Less as Prices Rise Might Pay Off for Farms in Unexpected Ways × An Ancient Sea Once Split North America Down the Middle. The Beautiful Multicolored Ammonite Shells From Its Waters Are so Perfectly Preserved That They Still Shimmer Today
Published 2026-07-12
0:00 / 18:53 · Narrator Sulafat/Charon/Vindemiatrix
In this episode
The Conversation
Fertilizers Carry a Hidden Cost for Soil’s Crucial Microbes – Using Less as Prices Rise Might Pay Off for Farms in Unexpected Ways
by Esther Ndumi Ngumbi, Assistant Professor, Department of Entomology; African-American Studies, University of Illinois Urbana-Champaign
The connection
Shimmering ammonite shells buried in the American Midwest are the literal foundation of the region's farmland. A piece from Smithsonian Magazine earlier this week traces how a prehistoric inland sea left behind the minerals that make this soil so productive. It’s striking to think that modern harvests rely on a 70-million-year-old graveyard. Yet, the health of that same dirt is under pressure. Writing on July 8th, Esther Ndumi Ngumbi points out that synthetic fertilizers might be choking the microscopic life that keeps crops healthy. Putting these observations together suggests that a farm's success depends on honoring a legacy of life that spans from the prehistoric deep to the invisible world currently living underfoot.
Esther Ndumi Ngumbi leaves the listener looking at the dirt beneath a tractor’s tires as a crowded, living city. The focus is on the immediate—how a farmer in Illinois or Iowa might trade expensive synthetic chemicals for the work of invisible fungi and bacteria. It’s a persuasive case for trusting the biology of the present to feed the world. But move from the microscopic to the prehistoric, and the ground starts to look even older. The piece from the Smithsonian shifts the perspective from the microbes currently swimming around corn roots to the massive marine lizards and shimmering ammonites that swam over the same spots 70 million years ago. While Ngumbi points to the natural workforce keeping plants alive today, this next story traces the origin of that fertile ground back to a salt-water sea that once split North America in two. It’s a striking pivot. One writer focuses on what’s living in the soil right now; the other suggests that the richness of the American prairie is actually a gift from a long-vanished ocean. Notice how the iridescent sheen of a fossilized shell in South Dakota isn't just a museum piece—it’s a clue to why the dirt in the Midwest is worth farming in the first place.
The dust kicked up by a tractor in Iowa was once the floor of a prehistoric ocean, filled with shells and salt. Today, that same ground houses billions of microscopic creatures working to keep the corn green. A field looks like a simple place to grow food, yet it binds together ancient fossils and modern microbes. What lingers is the image of the ground as a finite inheritance. If that’s true, how does one decide what to take and what to leave for the next thousand years?