Radiocarbon dating example
How It Works: Carbon has 3 isotopic forms: Carbon-12, Carbon-13, and Carbon-14.
The numbers refer to the atomic weight, so Carbon-12 has 6 protons and 6 neutrons, Carbon-13 has 6 protons and 7 neutrons, and Carbon-14 has 6 protons and 8 neutrons.
Looking at the graph, 100% of radiocarbon in a sample will be reduced to 50% after 5730 years.
In 11,460 years, half of the 50% will remain, or 25%, and so on.
The Mayan calendar used 3114 BC as their reference.
More recently is the radiocarbon date of 1950 AD or before present, BP.
In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.
One good example would be the elevated levels of Carbon-14 in our atmosphere since WWII as a result of atomic bombs testing.Plankton absorbs, Carbon-14 from the ocean much like terrestrial plants absorb Carbon-14 from the air.Since plankton is the foundation of the marine food chain, Carbon-14 is spread throughout aquatic life.The extra neutrons in Carbon-14’s case make it radioactive (thus the term, radiocarbon).Radiocarbon is produced in the upper atmosphere after Nitrogen-14 isotopes have been impacted by cosmic radiation.
Limitations and calibration: When Libby was first determining radiocarbon dates, he found that before 1000 BC his dates were earlier than calendar dates.