Bomb radiocarbon dating
When the slope was steep, the uncertainty was typically ± 1 year.Since 2000, that same measurement precision yields a chronological uncertainty of ± 2-4 years.In fact, the natural production of radiocarbon has varied as well. Before the industrial revolution, from 1800 - 1400 AD, the natural production of radiocarbon was high, so dates are "too young." From 1400 AD to 300 BC they are "too old," and prior to 300 BC , they are too young.
Caution must be exercised when dating an elevated sample since the pulse is double valued.
The surplus "bomb" radiocarbon is just one of the effects human have had on the ratio of C.
During the industrial revolution (1850 - present) increasing amounts of fossil fuels were combusted.
Nitrogen atoms high in the atmosphere can be converted to radiocarbon if they are struck by neutrons produced by cosmic ray bombardment.
The rate of bombardment is greatest near the poles, where the Earth's magnetic field is dipping into the Earth and therefore does not deflect incoming cosmic rays.
Search for bomb radiocarbon dating:
It is relatively easy to achieve 0.5-0.8% precision when analyzing recent full-sized samples.