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A group of researchers recently discovered an unusual radioactive anomaly at the bottom of the Pacific Ocean. Specifically, they found a radioactive isotope of beryllium known as beryllium-10 (10Be).
There’s something weird deep under the sea. The anomaly is characterized by a high concentration of the beryllium-10 isotope in the seafloor strata at two distant locations in the Pacific Ocean. The discovery suggests that it may represent a widespread phenomenon.
Experts are uncertain about the cause of the anomalous concentration, but they have several hypotheses. In particular, they believe it might be due to astrophysical events or changes in ocean currents. Regardless of the cause, the research team estimates that this event likely occurred around 10 million years ago.
The study findings were published in Nature Communications.
The result of a collision. Beryllium-10 is a rare isotope that forms on Earth when cosmic rays interact with the oxygen and hydrogen in the atmosphere. The resulting beryllium eventually falls into the ocean and binds to marine sediments.
The half-life of 10Be is around 1.4 million years. After this time, half of the beryllium nuclei will have decayed into boron. Like other radionuclides (unstable forms of elements that decay by releasing radiation to become more stable), beryllium-10 is valuable for geological dating.
Geological calendar. One of the most well-known radioisotopes is carbon-14, which is found in organic samples and has a relatively limited dating range. While carbon-14 can only be used to date objects up to 50,000 years old, beryllium-10 allows experts to date materials that are up to 10 million years old.
Surprising samples. Researchers found unexpected levels of beryllium by studying geological samples collected from the bottom of the Pacific Ocean, several miles deep. The team used accelerator mass spectrometry to measure the beryllium content and date the several layers of sediment.
They identified an anomaly in sediments dating back around 10 million years. In that region, the team found the concentration of 10Be to be twice as high as expected. Researchers also examined multiple samples to ensure that this finding wasn’t due to contamination.
Different hypotheses. The big question now is what caused the unexpected accumulation of beryllium-10. The research team proposes two possible hypotheses to explain this phenomenon: one related to ocean currents and the other to astronomical events.
The first hypothesis suggests that a sudden change in ocean circulation may have caused beryllium to be distributed unevenly throughout the oceans, leading to a concentration in the Pacific Ocean.
The second hypothesis explores two possibilities. The first possibility is that a supernova may have increased the atmospheric production of 10Be by exposing the Earth to a higher influx of cosmic rays. The second possibility considers a hypothetical decrease in the intensity of the Earth’s magnetic field. This would’ve reduced the protection of the atmosphere against cosmic rays, resulting in increased production of beryllium-10.
Image | Jeremy Bishop | HZDR | Koll, Lachner, et al. (2025)
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