A research team from The University of New Mexico has published findings that shed light on how an ancient plant could help scientists better understand Earth’s climate history. The study, led by Professor Zachary Sharp from the Department of Earth and Planetary Sciences, appears in the Proceedings of the National Academy of Sciences (PNAS) under the title “Extreme triple oxygen isotope fractionation in Equisetum.”
The research focuses on horsetails, a type of hollow-stemmed plant that has existed for over 400 million years. According to the study, water moving through these plants undergoes a natural distillation process so intense that its oxygen isotope ratios are similar to those found in meteorites or extraterrestrial materials.
“It’s a meter-high cylinder with a million holes in it, equally spaced. It’s an engineering marvel,” said Sharp. “You couldn’t create anything like this in a laboratory.”
The discovery provides new explanations for unusual oxygen isotope data previously observed in desert plants and offers scientists another method for reconstructing past climates, especially in dry regions. Oxygen isotopes serve as tracers that can reveal information about water sources, plant transpiration rates, and atmospheric humidity. However, heavier isotopes are rare and difficult to analyze under natural conditions.
Sharp’s team collected samples from smooth horsetails (Equisetum laevigatum) along the Rio Grande in New Mexico. They measured changes in isotope ratios from the base to the tip of each plant and found uppermost water samples with values not previously recorded on Earth.
In July, Sharp presented these results at the Goldschmidt Geochemistry Conference held in Prague. During his presentation he noted: “If I found this sample, I would say this is from a meteorite,” adding, “But in fact, these values do go down to these crazy low levels.”
With this new data, researchers have refined their models and gained insights into earlier unexplained results involving other desert plants. Sharp believes that such improved models could also be used to interpret ancient climate systems.
Fossilized horsetails—which once grew up to 30 meters tall—contain silica structures called phytoliths that may preserve isotope ratios for millions of years. These phytoliths function as what Sharp describes as a “paleo-hygrometer,” or an ancient gauge for measuring humidity.
“We can now begin to reconstruct the humidity and climate conditions of environments going back to when dinosaurs roamed the Earth,” said Sharp.
This study adds to ongoing geoscience research at The University of New Mexico and highlights horsetails as valuable indicators for understanding Earth’s environmental past.
