How much mercury is actually in the tomb of Qin Shi Huang? Experts say: The pomegranate trees on the mountain can explain everything.

The pomegranate trees on the mound covering the tomb of Qin Shi Huang are living evidence that unravels the mystery of mercury in the underground palace. These trees, which average only 1.5 meters in height, have twisted branches and sparse leaves, forming a stark contrast to the normal pomegranate trees outside the tomb area, which are three to four meters tall.

Geological sampling in 2002 showed that the mercury content in the soil around the tree roots reached 1440 ppb, 80 times that of ordinary soil, and the mercury absorption in the leaves exceeded edible standards by 20 times — they did not grow this way naturally, but were stunted by mercury vapor that volatilized underground.

This anomaly began with the first mercury measurement in 1981. The geological team found that the mercury concentration increased in a circular pattern within a 12,000 square meter area at the center of the mound, with the highest value being 25 times that of surrounding farmland. To eliminate interference from the soil background, the testers specifically compared the soil from the fish pond where the soil was taken from the mound, and the results showed normal mercury levels.

The distribution pattern of the mercury anomaly closely matches the description in the "Records of the Grand Historian" that states "mercury represents all rivers and streams": the highest concentration is on the northeast side, corresponding to the location of the Bohai Sea and Yellow Sea in the territory of the Qin Empire; the south side is next, echoing the Yangtze River Basin; and there are almost no anomalies in the northwest, which is exactly the water-scarce area of Longxi, the birthplace of the Qin state.

These data point to a fact: the mercury in the underground palace has been slowly volatilizing through cracks in the mound for over two thousand years. The stunting of the pomegranate trees is the result of long-term exposure to mercury vapor. Mercury vapor is seven times heavier than air and accumulates around the root system, inhibiting the plant's absorption of iron and magnesium, leading to chlorophyll synthesis being obstructed.

Archaeologists once tried planting poplar trees at the edge of the mound, and after three years, measurements showed that the growth rings of the poplar trees near the center were only one-third the width of those on the outskirts, while the pomegranate trees, due to their strong resistance to poor soil and adversity, became one of the very few tree species that could survive in mercury-polluted areas, thus becoming a natural "indicator of mercury pollution".

Experts estimated based on the excavation area of the underground palace (170 meters east-west and 145 meters north-south) and the depth of the mercury anomaly that if we assume an average thickness of the mercury layer of 10 centimeters, the total reserve could exceed 100 tons. This number needs to be understood in historical context: the Ba Guo Fu Qing's Ba Yu Dan Sha mine and the mercury mine in Xunyang, Shaanxi had already formed large-scale mining during the Qin and Han dynasties.

In the Xunyang mining area alone, over 3,000 ancient mine shafts have been discovered, and the Qin dynasty pottery unearthed here confirms that this was once a mercury refining base. According to the distillation technology of the time, 1 ton of cinnabar could yield 0.86 tons of mercury, so 100 tons of mercury would require at least 116 tons of cinnabar. This is equivalent to several years of production from the Ba Yu mining area, supplemented by Xunyang, to possibly meet the needs of the underground palace.

Moreover, the depth of the mercury anomaly corresponds with the structure of the underground palace. Geophysical surveys show that the stone palace walls 34 meters below the mound are intact, and the top of the burial chamber is 72 meters from the surface, with the mercury layer most likely located at the bottom of the burial chamber. For two thousand years, mercury vapor has risen along the rammed earth seams, forming a "mercury gas belt" in the middle of the mound, precisely affecting the vegetation on the surface.

A laser radar scan in 2025 discovered 12 radioactive fissures inside the mound, 2-5 centimeters wide, which have become "highways" for mercury vapor diffusion.

Today, staff in the tomb area regularly trim these stunted pomegranate trees to prevent fruit from falling and causing pollution. Visitors must wash their hands immediately after touching the trunks, as the mercury content absorbed by the bark can reach 0.5 ppm.

These seemingly ordinary trees are, in fact, a link between history and science — they prove with their twisted branches that Sima Qian's account of "mercury representing all rivers and streams" is not an exaggeration, but rather evidence of ancient China's mobilization of national resources to mine mercury across mountains and rivers.

As technology brings the "liquid landscape" of two thousand years ago into view, the pomegranate trees on the mound continue to silently tell the story of the silver ocean that never solidifies deep within the underground palace.