This prehistoric plant produces water that seems to come from another world

A discovery that challenges our assumptions

This water seems to have come straight from space. Yet it is indeed from Earth, extracted from the hollow stem of a prehistoric plant that is still very much alive: Equisetum, better known as horsetail. Analyses have revealed that this water possesses the most extreme oxygen isotopic signature ever measured in a terrestrial material.

This discovery does more than just push the known chemical boundaries of water on our planet. It forces scientists to rethink how plants, fossils, and even desert climates account for the phenomenon of evaporation. A single plant stem has just added a new layer of complexity to a picture we thought we had mastered.

The Surprising Mechanism of the Horsetail Stem

The mystery lies along the smooth, jointed stem of the horsetail. By collecting water samples from the base to the tip of the plant, Dr. Zachary Sharp of the University of New Mexico uncovered a fascinating process. As water rises through the stem, its oxygen composition undergoes a gradual yet radical transformation.

At the base, the levels fall within a typical natural range. But the closer one gets to the tip, the higher they climb, reaching levels of enrichment never before observed. The stem itself concentrates heavy oxygen as moisture escapes into the dry air, long before the water reaches even a single leaf. The fact that this transformation occurs within a single plant—rather than in an extreme environment such as a salt lake—calls for a closer examination of the mechanisms of evaporation.

The process is relentless. At each segment of the stem, water evaporates through the wall. Water molecules containing lighter oxygen escape first, leaving behind those with heavier oxygen. Each upper section therefore receives water that is already enriched, which in turn evaporates, creating an extreme gradient toward the top. Dry wind and heat can intensify this phenomenon, offering a new explanation for certain strange isotopic data observed in desert plants.

Oxygen, a Chemical Telltale

The oxygen content in water is not uniform. It carries a chemical signature that allows scientists to trace the origin of the moisture and its path. A water sample contains several types of oxygen, called isotopes, which are atoms of the same element but with different masses. It is the ratio between these isotopes that tells a story.

During evaporation, nature performs a simple sorting process: molecules containing light oxygen—which are more volatile—evaporate first. The remaining liquid therefore becomes concentrated in heavy oxygen. Without careful interpretation, this sorting can skew analyses and make a lake, a leaf, or a fossil appear wetter or drier than it actually was.

To circumvent this pitfall, Zachary Sharp’s team simultaneously tracked three different forms of oxygen. This approach is crucial because heavy oxygen is rare, and slight biases can go unnoticed if only a single ratio is measured. By analyzing three signals at once, the researchers were able to test models of water circulation in plants with a level of precision that standard measurements cannot achieve.

When a Plant Transcends the Boundaries of the Solar System

Horsetail is not just any plant. Its history dates back to the Devonian period, about 400 million years ago, reflecting an exceptionally long lineage. It was in the water within its stem that the proportion of heavy oxygen reached its peak—so much so that Dr. Sharp reacted by saying, “If I had found this sample, I would have said it came from a meteorite.”

This finding has quite simply expanded the known range of oxygen signatures on Earth and in the solar system fivefold, providing modelers with a new physical limit to incorporate into their calculations. But the story doesn’t end there. Horsetails are among the greatest accumulators of silica in the plant world. Within their tissues, they form tiny glassy structures called phytoliths, which can survive long after the plant has died.

However, data from Sharp’s team revealed a major discrepancy: the oxygen isotope signature in the silica of the phytoliths did not match that of the water circulating in the stem. This discrepancy is a serious warning. It means that analyses of fossil phytoliths—especially if they are based on an average of the entire stem—may tell us a false story about past humidity.

Correcting Models to Better Understand the Past

Scientific models that predict the chemistry of water in plants rely on a number of constants. One of them turned out to be slightly inaccurate. Using measurements taken along the entire length of the horsetail stem, Zachary Sharp’s team was able to adjust a key parameter in the evaporation models so that it better matches how water vapor actually moves through dry air.

This update helped explain previously puzzling oxygen readings in desert animals and plants that drink highly evaporated water. Refining these constants won’t resolve all uncertainties, but it reduces the risk of attributing to biology a signal that was actually dictated by physics.

Scientists have long used oxygen signals from fossil phytoliths to estimate the humidity of ancient climates. Since air humidity influences the rate at which water escapes from plants, the isotopic signature left behind can reflect how dry the air was. As Dr. Sharp points out: “We can now begin to reconstruct the humidity and climatic conditions of environments dating back to the time when dinosaurs roamed the Earth.” He qualifies this, however, by noting that the variation observed in phytoliths limits what these fossils can reveal without additional context.

A Scientific and Educational Adventure

This breakthrough was made possible by a collaborative approach. A summer course combined fieldwork with laboratory analysis, allowing students to gain hands-on experience with real-world data. Fourteen of them participated in collecting the stems and measuring the oxygen signatures at the University of New Mexico’s facilities.

Back in Albuquerque, New Mexico, the Stable Isotope Center analyzed the samples, while electron microscopes examined the silica forming within the stems. This hands-on approach is essential, as climate tools advance more rapidly when students and seasoned scientists apply them together to the complexities of nature.

Ultimately, the extreme isotopic signatures of horsetail water provide scientists with a new tool for testing climate models and fossil indicators. Future work will need to map similar signals in other plants and environments, particularly where drought pushes evaporation to its limits. The study was published in the journal Proceedings of the National Academy of Sciences.

Source: earth.com

This prehistoric plant produces water that seems to come from another world