“This Is From a Meteorite”: Scientist Stunned by Water Inside 400-Million-Year-Old Plant

Ancient horsetails may hold the key to understanding Earth’s prehistoric climate.

A group of scientists from The University of New Mexico has discovered that an ancient and unusual plant could hold the key to revealing details about Earth’s distant climate history.

The research, led by Zachary Sharp, a professor in UNM’s Department of Earth and Planetary Sciences, was recently published in the Proceedings of the National Academy of Sciences (PNAS). The study centers on horsetails, a family of hollow-stemmed plants that have survived on Earth for more than 400 million years.

The researchers found that water moving through these plants experiences such a powerful natural purification process that its oxygen isotope composition closely matches that of meteorites and other materials from beyond our planet.

“It’s a meter-high cylinder with a million holes in it, equally spaced. It’s an engineering marvel,” Sharp said. “You couldn’t create anything like this in a laboratory.”

Decoding Desert Mysteries

The team’s discovery sheds light on long-standing questions about oxygen isotope patterns in desert plants and provides scientists with a new way to study past climate conditions, particularly in dry regions.

In water, oxygen isotopes serve as natural markers that help researchers trace where the water originated, how quickly plants release it through transpiration, and what the surrounding humidity levels might have been. However, because the heavier isotopes are present in only tiny quantities, it has been challenging to accurately model how their ratios shift under real-world environmental conditions.

Sharp’s team collected samples from smooth horsetails (Equisetum laevigatum) along the Rio Grande in New Mexico, measuring how the isotope ratios evolved from the plant’s base to its tip. The uppermost water samples showed unprecedented readings, values that previously seemed to fall far outside of the range of anything on Earth.

This past July, Sharp had the opportunity to present this research at the Goldschmidt Geochemistry Conference in Prague.

“If I found this sample, I would say this is from a meteorite,” Sharp said during the conference. “But in fact, these values do go down to these crazy low levels.”

Rewriting Climate Models

The new data allowed the researchers to refine their models, offering fresh insights into previously unexplainable results from other desert plants. Sharp believes these improved models could be used to understand ancient climate systems as well.

Fossilized horsetails, which once grew up to 30 meters tall, contain tiny silica structures called phytoliths that may preserve isotope ratios for millions of years. These phytoliths act as a “paleo-hygrometer,” or an ancient humidity gauge, according to Sharp.

“We can now begin to reconstruct the humidity and climate conditions of environments going back to when dinosaurs roamed the Earth,” he said.

This research adds to UNM’s growing contributions to geosciences and positions horsetails — some of nature’s oldest survivors — an unlikely but powerful climate storytellers.

Reference: “Extreme triple oxygen isotope fractionation in Equisetum” by Zachary Sharp, Jordan Wostbrock, Anthony Gargano, Vincent Hare, Jessica Johnson, Thure Cerling, Payal Banerjee, Catherine Peshek, Cloe Knutson, Lauren Hartzell, Erick Cano, Elena Stiles, Kelley R. Bassett, Kira Holland, Michael H. Dowd, Jarunetr (Nadia) Sae-Lim, Teresa Dominguez, Dalton Bryant, Eduardo Di Marcantonio, Jensen Wainwright, Maxwell Horsford, Paul Botté, Catherine Gagnon, Paula J. Rudall and James Ehleringer, 28 October 2025, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2507455122

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