Scientists now say their key tool for dating ancient artifacts might be wrong by 10,000 years, which could push back the timing of key events in history and improve our understanding of climate change and ancient civilizations.

Their study could force to rethink the dates when events occurred, especially the period when modern humans lived alongside Neanderthals in Europe. It suggests that modern humans might have lived in Europe far longer than thought and that prehistoric paintings recently found in the Chauvet cave, in southern France, might be 38,000 years old rather than the estimated 33,000 years.

A research team made up of English and American scientists found large variations in levels of the carbon-14 isotope, which is used as the basis of carbon dating, preserved in a 19 inch stalagmite recovered from a submerged cave in the Blue Holes of the Bahamas. These are limestone caverns that were created when sea levels were nearly 330 feet lower than they are today.

These findings suggested dramatic changes in the amount of radioactive carbon in Earth?s atmosphere during the last Ice Age, probably as a result of changes in the strength of the planet?s magnetic field. The field shields Earth from the cosmic rays that create carbon-14 in the atmosphere, and this would have altered the levels of the isotope during the past 45,000 years.

Dr. David Richards of the University of Bristol, who did the study with colleagues in Arizona and Minnesota, says, ?Beyond about 20,000 years ago there are some dramatic swings in radiocarbon concentration, which means the age offset between the radiocarbon age and true calendar age can be up to 8,000 years.? This means that radiocarbon dating, which depends on the steady decay of carbon-14, is less reliable if an artifact is older than 16,000 years.

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