The Silent Accusation of the Pomegranate Tree — Biological Evidence of the Mercury Mystery in the Qin Mausoleum Underground Palace

When you walk into the sealed mound of the First Emperor’s mausoleum, those twisted branches and sparse leaves inevitably draw attention. These pomegranate trees, averaging only 1.5 meters in height, form a striking contrast with the surrounding farmland edges outside the mausoleum area, which are three to four meters tall and of normal size. They are not naturally dwarfed but have been stunted by an invisible “poison” force.

Horrific Data Revealed by Soil Testing

Geological sampling in 2002 opened a door to scientific discovery. Detectives found astonishing levels of mercury in the soil near the tree roots—1440ppb, which is 80 times higher than normal farmland soil. The mercury absorption in the leaves was even more shocking, exceeding safety standards for consumption by 20 times. This is not a genetic issue with the trees but a long-term consequence of mercury vapor volatilized from underground.

Tracing the origin of this discovery points back to 1981. The geological team conducted the first mercury content measurement within a 12,000-square-meter area at the center of the sealed mound, revealing a ring-shaped distribution of increasing mercury concentration, with the highest value being 25 times the levels measured in surrounding farmland. To eliminate interference from the soil’s natural mercury content, the team even compared these samples with soil data from the original source—the fish pond soil—showing that the mercury levels in that area were completely normal. This indicates that the abnormality comes entirely from underground.

Remarkable Correlation Between Historical Records and Modern Data

Even more astonishing is that the spatial distribution pattern of these mercury anomalies perfectly matches the geographic descriptions in the “Records of the Grand Historian,” which states “using mercury for rivers and streams.” The highest mercury concentration is in the northeast, corresponding precisely to the locations of Bohai and the Yellow Sea within the Qin Empire’s territory; the second highest is to the south, reminiscent of the Yangtze River basin under Qin rule; and almost no anomalies are detected in the northwest, which coincides with the origin of the Qin state and the sparsely waterlogged Longxi region. Over a span of two thousand years, ancient texts and modern instrument readings point to the same fact.

Biological Mechanism of Mercury Vapor Torture

The dwarfing of the pomegranate trees fundamentally results from long-term exposure to mercury vapor. Mercury vapor is seven times denser than air and deposits around plant roots, interfering with the absorption of key microelements like iron and magnesium, thereby hindering chlorophyll synthesis. The result is the twisted branches and sparse leaves we see.

Archaeologists once conducted a trial planting at the edge of the sealed mound. They planted poplar trees, and after three years, measuring the annual rings showed that poplars near the mercury anomaly center had rings only one-third the width of those farther away. But pomegranate trees are different—they have inherently resilient roots that tolerate poor soil and adversity, making them one of the few species capable of surviving in mercury-contaminated environments. As a result, they inadvertently became natural “mercury pollution bioindicators.”

Estimating Reserves: Historical Context

Based on the actual excavation area of the underground palace (170 meters east-west, 145 meters north-south) and the depth of mercury influence, experts made a bold estimate. Assuming an average mercury layer thickness of 10 centimeters, the total mercury stored inside the mausoleum could reach over 100 tons.

This figure must be understood within the context of mining activities during the Qin and Han dynasties. The Baguo widow’s Bayu cinnabar mine and the mercury mines in Qinggou, Xunyang, Shaanxi, had already been scaled up at that time. Over 3,000 ancient mines have been discovered in the Xunyang area, and Qin Dynasty pottery jars excavated there confirm it was once an industrial base for mercury extraction. Based on the distillation technology of that era, 1 ton of cinnabar could produce 0.86 tons of mercury. Therefore, the demand for 100 tons of mercury would require at least 116 tons of cinnabar, which is equivalent to several years of production from the Baguo mines plus additional from Xunyang, enough to meet the needs of the underground palace.

Physical Structure and Mercury Vapor Ascent Pathways

Even more intriguing is that the depth distribution of mercury anomalies perfectly matches the actual structure of the mausoleum. Geophysical data show that the stone walls of the tomb are intact at 34 meters below the sealed earth, and the tomb chamber’s top is 72 meters below the surface, indicating that the mercury layer likely resides at the bottom of the tomb chamber. Over two thousand years, mercury vapor has slowly risen along tiny cracks between rammed earth layers, forming a “mercury gas belt” in the middle of the sealed earth, which has affected the growth of surface vegetation.

In 2025, laser scanning provided new insights. Researchers discovered 12 radial fissures within the sealed earth, each 2-5 centimeters wide. These natural channels serve as “highways” for mercury vapor diffusion, allowing underground mercury vapor to continuously and steadily seep upward.

Current Protective Measures and Eternal Testimony

Today, staff in the mausoleum area regularly prune these dwarf pomegranate trees to prevent fallen fruit from polluting the environment. Even visitors’ contact with the tree trunks must be cautious—mercury content on the bark can reach 0.5ppm, and immediate handwashing is required after contact.

These seemingly ordinary trees are actually living bridges connecting history and science. Through their twisted branches and sparse leaves, they prove to the world that Sima Qian’s romantic description of “using mercury for rivers and streams” is not an exaggeration but a tangible testament to ancient China’s mobilization of the entire nation to extract mercury resources across mountains and rivers. As modern technology gradually reveals the outline of that “liquid landscape” from two thousand years ago, the pomegranate trees on the sealed earth continue to silently tell the story of an unsolidified silver ocean deep within the tomb.