Scientists have created a way to date Earth's densest and oldest polar ice by studying the composition of krypton gas trapped within old air bubbles, according to an Oregon State University press release.
Research was published this week in the journal PNAS.
Researchers used a new dating method called Atom Trap Analysis (ATTA) to analyze the ice, which was recovered from the McMurdo Dry Valleys in Antarctica.
"The oldest ice found in drilled cores is around 800,000 years old and with this new technique we think we can look in other regions and successfully date polar ice back as far as 1.5 million years," said Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the PNAS article. "That is very exciting because a lot of interesting things happened with the Earth's climate prior to 800,000 years ago that we currently cannot study in the ice core record."
Buizert and his colleagues said potential uses include dating meteorites found in Antarctic ice, analyzing the Earth's cycle of ice ages and climate, according to the release.
Krypton is a noble gas that can be found in the atmosphere at low levels or approximately one part per million, according to the release. In the upper atmosphere, exposure to cosmic rays could transform a krypton isotope into a decaying radioactive isotope.
Air bubbles in ancient polar ice contains some of these radioisotopes, according to the study. Researchers can determine how long the gas has been trapped in the ice by comparing the stable krypton isotopes to the radioisotope's state of decay.
This is basically how the researchers used carbon-14 techniques to date the ice. This method is only accurate back to approximately 50,000 years, according to the study.
"That is very exciting because a lot of interesting things happened with the Earth's climate prior to 80,000 years ago that we currently cannot study in the ice core record," Buizert said.
Due to the small amount of krypton in the air, a great deal of ice has to be melted first to obtain enough samples. A device that's able to count, or trap, individual atoms is also required, according to the release.
The device was developed in 2011 by a team of nuclear physicists from Argonne National Laboratory in Illinois.
The study's authors obtained over 600 pounds of ice chunks from Taylor Glacier, Antarctica, melted them, and trapped the escaped air in flasks in order to test the atom trap.
They estimated that the ice was approximately 120,000 years old. Now the authors want to find older ice.
"Most people assume that it's a question of just drilling deeper for ice cores, but it's not that simple," said study co-author Edward Brook, an Oregon State University geologist, according to the release. "Very old ice probably exists in small isolated patches at the base of the ice sheet that have not yet been identified, but in many places it has probably melted and flowed out into the ocean."
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