A European-Australian research team has encountered an unexpected accumulation of the rare radioactive isotope beryllio-10 at the bottom of the Pacific Ocean. Draed about 10 million years ago, this anomaly can serve as a global “time marker” that will improve geological dating methods in the deep past.
But the mystery remains why much of this isotope has been present for 10 million years, and the answer can be out of this world.
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The beryllium-10 is an example of radionuclide: atomic nuclei (known as isotopes) that decompose in other elements over time by releasing protons or neutrons.
If an isotope is known at a stable speed and its half -life (the time that has been half of the ‘father’ atoms in ‘daughter’), scientists can measure the relative concentrations of elements in a given sample and calculate their age.
This is called radiometric dating, and can be used to determine the age of ancient things from a rock to a fossil and a wooden artifact.
The most common method is carbon dating, using the radioactive carbon isotope, 14C. but 14C only has a short half life of approximately 5,700 years.
Credit: Hzdr / Blrck.de
“The radiocarbon method is limited to dating samples of no more than 50,000 years,” says Dominik Koll, physicist from Helmholtz-Zentrum Dresden-Rossendorf (Hzdr) and author aimed at recent research. “To date, the oldest samples, we need to use other isotopes, such as cosmogenic beryllium-10 (10Be).”
This isotope has a half -life of 1.4 million years, allowing researchers to give objects 10 million years ago.
For example, 10BE has previously been used to delay the fossil dating of Australopithecus for one million years, and to confirm a massive solar storm indicated by the rings of the old trees.
Koll’s research group discovered an unexpected amount of 10Be in samples of Ferromanganesa cortex, taken from the seabed of the Pacific Ocean.
Formed slowly and constantly of iron and manganese, this cortex is “one of the most pristine geological archives”, as Koll and their colleagues write in their new article.
When the team measured its 10Being happy, the results were surprising.
“In about 10 million years, we find almost double 10Be as we had anticipated, ”reports Koll. “We had found an anomaly previously discovered.”
This deviation could improve geological dating methods in a deep time, providing an independent ‘time’ marker to help synchronize different data sets.
“For periods that cover millions of years, such markers of cosmogenic time still do not exist,” explains Koll. “This beryllium anomaly has the potential to serve as a marker.”
The unsolved anomaly
But the question remains: why does this surprising accumulation exist?
The key may be how 10Be is formed. The vast majority are created when cosmic rays crash against the Earth’s atmosphere and interact with oxygen and nitrogen atoms. He 10Be is deposited throughout the planet through precipitation. On Earth, it is fixed in soils, locked in ice or transported through river systems. Some isotopes reach the seabed, where slow growth manganese nodules can absorb it.
The research team suggests two possible explanations for the massive accumulation of 10Be 10 million years ago.
First, the evidence suggests that about 10 to 12 million years ago, oceanic circulation around Antarctica changed dramatically. This may have caused 10Be to distribute unequally around the planet, with a concentration in the Pacific.
Alternative options are astrophysical. The researchers propose that a supernova may have exploited near the earth at this time, temporarily increasing the cosmic rays that bombard our atmosphere and increase the general production of 10Being. Or, perhaps the Earth’s protective helosphere was damaged, leaving it more vulnerable to cosmic rays.
“Only the new measurements can indicate whether the beryllium anomaly was caused by changes in ocean currents or has astrophysical reasons,” says Koll.
The investigation appear In the newspaper Nature communications.
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