Ice carbon dating
Comparing the proportion of stable-to-radioactive isotopes provides the age of the ice.
Though scientists have been interested in radiokrypton dating for more than four decades, krypton-81 atoms are so limited and difficult to count that it wasn't until a 2011 breakthrough in detector technology that krypton-81 dating became feasible for this kind of research.
"Most people assume that it's a question of just drilling deeper for ice cores, but it's not that simple," said Edward Brook, an Oregon State University geologist and co-author on the study.
"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." There also are special regions where old ice is exposed at the edges of an ice field, Brook pointed out.
Living organisms are constantly incorporating this C-14 into their bodies along with other carbon isotopes.
When the organisms die, they stop incorporating new C-14, and the old C-14 starts to decay back into N-14 by emitting beta particles.
The researchers determined from the isotope ratio that the Taylor Glacier samples were 120,000 years old, and validated the estimate by comparing the results to well-dated ice core measurements of atmospheric methane and oxygen from that same period.
Now the challenge is to locate some of the oldest ice in Antarctica, which may not be as easy as it sounds.
Scientists have discovered new relationships between deep-sea temperature and ice-volume changes to provide crucial new information about how the ice ages came about.
The new atom counter, named Atom Trap Trace Analysis, or ATTA, was developed by a team of nuclear physicists led by Zheng-Tian Lu at Argonne National Laboratory near Chicago.
In their experiment at Taylor Glacier in Antarctica, the researchers put several 300-kilogram (about 660 pounds) chunks of ice into a container and melted it to release the air from the bubbles, which was then stored in flasks.
"The international scientific community is really interested in exploring for old ice in both types of places and this new dating will really help," Brook said.
"There are places where meteorites originating from Mars have been pushed out by glaciers and collect at the margins.
Radiocarbon dating can easily establish that humans have been on the earth for over twenty thousand years, at least twice as long as creationists are willing to allow.