Stalagmites found in a cave in China is being hailed as the "Holy Grail" for accurate radiocarbon dating by scientists.
A new study revealed that a pair of stalagmites inside the Hulu Cave near Nanjing, China has a seamless, chronological atmospheric record dating back from the last Ice Age. The stalagmites can refine the calibration of carbon-14, making dating of artifacts a lot more precise.
Details of the stalagmites were published in the journal Science.
Recalibrating Radiocarbon Dating
Radiocarbon dating, a method developed in the 50s, is used by archaeologists to date organic compounds accurately. It is based on radioactive carbon-14 which is continuously created.
While reliable, radiocarbon dating needs calibrating based on the level of carbon-14 in the atmosphere that varies from year to year. Trees and stalagmites can be used to calibrate, but the former only goes back to around 13,000 years ago and the latter can be a little unreliable. Sometimes, the measurement of carbon-14 in stalagmites are skewed by "dead carbon" that dilutes the substance.
'Holy Grail' Of Carbon Dating
However, scientists led by Hai Cheng of Xi'an Jiaotong University discovered stalagmites that have unusually low levels of dead carbon, allowing an accurate carbon-14 calibration way beyond the limits of tree rings.
"The Hulu carbon-14 dataset provides a robust reconstruction of the atmospheric carbon-14 history beyond the current tree ring limit of around 14,000 years before present," explained Cheng. "This is a substantial contribution toward the refinement of the carbon-14 calibration curve."
The stalagmites have an unbroken record from 54,000 years ago. The team used a highly reliable technique called thorium-230 dating to analyze hundreds of layers within the stalagmites and establish a chronological baseline for a more precise radiocarbon dating.
Larry Edwards, a geologist from UC Berkeley, co-author of the study, and one of the people who developed the thorium-230 technique shared to Gizmodo that the stalagmites also contain carbon derived from limestones inside the cave. To make an accurate analysis, the team had to make corrections for limestone-derived carbon but found that the stalagmites have very little of the substance.
"The new Hulu record has less uncertainty and resolves previously unknown fine-scale structure," added Cheng.
For archaeologists, the discovery means they can date the organic compounds from 14,000 to 54,000 years ago more accurately and confidently. The data could also be of use to climate scientists who wanted to gauge atmospheric changes from thousands of years ago.