Wild Ungulates on Lake Baikal May Be Eating Earth for Its Rare-Earth Elements
Along the western shore of Lake Baikal, wild ungulates are repeatedly visiting patches of carbonate-rich earth and eating the soil—an unusual behavior known as geophagy. A new study suggests that these animals may not be seeking only salt, clay, or calcium, as conventional explanations for mineral-lick visits often propose. Instead, the earth may provide unusually accessible rare earth elements (REEs), a group of metals better known for their role in electronics, magnets, and green technologies than for their possible biological significance. Geological and hydrobiogeochemical investigations in the valleys of the Sredniye Homuty and Hargino streams indicate that the animals’ mineral licks contain REEs in forms that can be released under the mildly acidic conditions of a ruminant’s abomasum, the stomach compartment where digestion becomes strongly acidic.
The finding adds a surprising dimension to one of nature’s most widespread but still poorly understood behaviors. Deer, elk, moose, wild sheep, cattle, elephants, primates, parrots, and other animals have all been observed deliberately consuming soil, clay, weathered rock, or mineralized water. Such behavior can help animals obtain sodium and other minerals, neutralize plant toxins, buffer digestive acidity, or supplement nutrients missing from their diets. In the Lake Baikal region, however, the researchers found a particularly distinctive chemical setting. The surrounding mountain-taiga landscapes formed largely on carbonate rocks contained very little sodium, while the available food had an imbalanced calcium-to-magnesium-to-phosphorus ratio. The study argues that the earth itself may offer a chemically targeted supplement unavailable in the local vegetation.
The researchers measured an average sodium concentration of 0.0431 grams per kilogram in dry grass, including sedges of the genus Carex, collected from the study area. That concentration was broadly comparable to the quantity of sodium available to animals in the carbonate “kudurits,” the earthy materials consumed at mineral licks. This result weakens the idea that sodium alone explains the animals’ attraction to the sites. The team also calculated a calcium:magnesium:phosphorus ratio in the feed of approximately 3:1:1, compared with a cited nutritional reference ratio of 0.6:1:1. Because calcium, magnesium, and phosphorus compete and cooperate in absorption, bone formation, muscle function, and cellular signaling, such an imbalance could create physiological pressure for animals to seek other mineral sources. Yet the most striking contrast emerged from the rare earth measurements.
When the researchers simulated the acidic environment of the abomasum using hydrochloric acid adjusted to approximately pH 2, the carbonate earth released an average of 13.461 milligrams of rare earth elements per kilogram. The amount extracted from the mineral-lick material was about 50 times greater than the corresponding amount available in plant food. This distinction is crucial: total elemental concentration does not necessarily equal biological availability. Minerals locked inside resistant crystal structures may pass through the digestive tract with little interaction, whereas ions weakly attached to clay surfaces, carbonates, or weathered mineral phases can dissolve under acidic conditions. The experiment was designed to estimate that potentially accessible fraction, although it did not directly measure how much REE ultimately enters an animal’s bloodstream.
Rare earth elements are not a single nutrient in the same sense as sodium, iron, or phosphorus. The group includes the 15 lanthanides, along with scandium and yttrium, and they often occur together because of their similar chemical behavior. Most exist in the +3 oxidation state and readily bind to oxygen-containing minerals and organic compounds. Their tendency to substitute for calcium in some mineral lattices is particularly relevant to biology: ionic sizes and charges can be similar enough for lanthanides to interact with calcium-sensitive proteins, cell membranes, and bone-related processes. Laboratory and animal studies have reported effects of elements such as lanthanum and cerium on cellular signaling, calcium-dependent phenomena, bone formation, metabolism, and nervous-system function. Other studies have documented toxicity at excessive exposures. The new research therefore does not establish that REEs are essential nutrients for Baikal’s ungulates; it proposes that they may influence physiology at trace levels and help explain a behavior that sodium deficiency alone cannot.
The suggested mechanism centers on the neuroimmunoendocrine system, a network linking the nervous, immune, and endocrine systems. These systems communicate through hormones, neurotransmitters, cytokines, and shared molecular receptors, coordinating stress responses, metabolism, reproduction, growth, and defense against disease. Because rare earth ions can interact with calcium channels, cell membranes, enzymes, and signaling pathways, the authors propose that accessible REEs might have subtle biological effects across this network. Such a hypothesis remains provisional. The study did not demonstrate a specific REE deficiency, identify a receptor or pathway in the wild animals, or show that consuming the earth changes health, behavior, or reproductive success. Instead, it combines geochemical measurements with previous physiological research to suggest a testable explanation: animals may be responding to a trace-element landscape that is invisible to conventional nutritional surveys focused on major minerals.
The geology of the Lake Baikal shore may be central to the phenomenon. Carbonate rocks weather through reactions involving carbonic acid in rainwater and soil, gradually releasing calcium and creating alkaline or weakly buffered environments. As rocks break down, clay minerals and fine particles can retain trace metals on charged surfaces. Changes in acidity, organic matter, drainage, and redox conditions can then determine whether those elements remain locked in the soil or become mobile. The study’s target valleys appear to combine carbonate-derived soils with vegetation that is poor in sodium and exceptionally low in total REEs. In that context, localized weathering products may act as “geochemical anomalies”: small patches of earth containing a chemically unusual and potentially more accessible mixture than the wider landscape. Animals could locate them through taste, smell, learned movement patterns, or repeated use of sites passed through generations.
The results also complicate the popular image of a mineral lick as a simple salt block provided by nature. Mineral licks are chemically diverse, and different species may visit the same site for different reasons. Clay can adsorb alkaloids and other plant compounds, potentially reducing toxicity; it can also bind water and influence gut contents. Carbonate material may buffer acids, while particular trace elements could affect digestion or metabolism. The researchers’ earlier work in other regions has linked geophagy to rare-earth anomalies, whereas studies in landscapes with low REE concentrations have shown that ungulates may still consume earth, indicating that no single explanation applies everywhere. Food chemistry, seasonal changes, pregnancy, lactation, parasite exposure, and the mineral composition of local rocks may all contribute. The Lake Baikal study is best understood as evidence for a context-dependent nutritional behavior rather than a universal prescription for why animals eat soil.
There is also a reason for caution before translating the finding into claims about “natural supplements.” Rare earth elements can be biologically active without being beneficial, and their effects depend on dose, chemical form, route of exposure, and the animal’s physiology. Some compounds are poorly absorbed and can remain in the gastrointestinal tract; others may cross biological barriers or accumulate in tissues. Laboratory research has reported adverse effects from prolonged or high exposure to certain REEs, including possible impacts on the nervous system and other organs. The Baikal investigation measured extractability under simulated stomach conditions, not long-term safety or nutritional benefit in living deer, elk, or other ungulates. It also did not determine the exact mixture of elements responsible for the high extractable value. More work will be needed, including measurements of blood and tissue concentrations, controlled feeding experiments, seasonal dietary surveys, and observations linking lick use with age, sex, pregnancy, health, and reproductive status.
For now, the study offers a vivid example of how animal behavior can reveal hidden connections between geology and physiology. A trampled patch of earth beside a Siberian stream may look like mud or weathered rock, yet its mineral chemistry could reflect ancient bedrock, modern water movement, plant uptake, and the digestive chemistry of the animals that visit it. By showing that Baikal’s carbonate earthy substances release far more rare earth material under abomasum-like acidity than local plant foods, the researchers have identified a plausible reason for the ungulates’ persistent geophagy and opened a new question about trace elements in animal biology. The next breakthrough may come not from finding another mineral lick, but from proving whether the rare earths in these licks are merely tolerated passengers, useful supplements, or signals that animals have evolved to seek in landscapes where the chemistry of life is written into the ground.
