Strange signal from the bottom of the ocean detected by scientists for first time

We already know a lot about Earth's history, there's still so much we need to find out.

Scientists are still searching for methods to date ancient geological events, for example. However a surprising discovery from the bottom of the Pacific Ocean may provide a new key method for dating key historical geological events dating back millions of years.

A new study, involving the discovery of a signal dating back 10 million years, could serve as a global time marker and improve how scientists synchronise geological records that span millions of years. A research team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), working with TUD Dresden University of Technology and the Australian National University (ANU), found an unexpected increase in a very rare radioactive isotope in seabed samples from the Pacific.

Items found by archaeologists, such as bones, or wood remnants, can be dated fairly accurately this way. But there's a problem. “The radiocarbon method is limited to dating samples no more than 50,000 years old,” HZDR physicist Dr. Dominik Koll explained. “To date older samples, we need to use other isotopes, such as cosmogenic beyllium-10 (10Be).”

Beryllium-10 , the rare isotope, is formed when cosmic rays with lots of energy hit oxygen and nitrogen in Earth's upper atmosphere. It then falls to Earth with rain and builds up in ocean sediments over time. With a half-life of 1.4 million years, it helps scientists track events from up to 10 million years ago, making it a valuable tool for studying Earth’s ancient history.

Koll and his team analysed ferromanganese crusts collected from several kilometres beneath the Pacific Ocean. The crusts collected are rich in iron and manganese and form slowly over millions of years, preserving a record of changes in the environment.

The samples were purified using a technique called Accelerator Mass Spectrometry (AMS) which also allowed them to measure the ¹⁰Be content with high accuracy.

The researchers were met with a surprise. Koll recalled: “At around 10 million years, we found almost twice as much 10Be as we had anticipated. We had stumbled upon a previously undiscovered anomaly.

“As a result, 10Be could have become particularly concentrated in the Pacific Ocean.”

Another hypothesis suggests a nearby supernova could have increased cosmic ray intensity, leading to a rise in ¹⁰Be production. The plan now is to analyse more samples in the future. If the anomaly is seen worldwide, the astrophysical hypothesis would gain support. If it is localised, changes in ocean circulation would be a more likely cause.

This anomaly still has the potential to completely flip geological dating. Koll said: “For periods spanning millions of years, such cosmogenic time markers do not yet exist. However, this beryllium anomaly has the potential to serve as such a marker.”

The study was published in Nature Communications.

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