Carbon analysis
All organisms absorb the carbon isotope C14 during their lifetime, but the intake stops when the organism dies. By measuring the amount left in the remains, one can calculate how old they are.
Using the carbon method, scientists can date the remains of both plants and animals back up to 50,000 years or so.
The isotope C14 is a radioactive substance that forms in the atmosphere due to the effect of cosmic radiation on nitrogen.
This radioactive carbon is part of the biological cycle on Earth and is absorbed by plants as well as animals and humans. When the organism dies, the intake of C14 stops and the breakdown of the material begins. It literally reduces its amount over time.
Carbon atoms usually have six protons and six neutrons, and ordinary carbon is therefore called C12. However, this heavier isotope, C14, has eight neutrons.
Today, only a thousandth of a gram is needed to determine the age of the remains of an organism. The sample is placed in an accelerator which, in the simplest terms, can distinguish the heavy C14 from the normal C12.
The carbon method is not completely accurate
The so-called half-life of carbon-14 is 5,730 years, but after that time only half of the original amount remains.
And after a double half-life, only 25% of the original amount of C14 remains.
However, the measurement method is not completely accurate because the C14 content of the atmosphere is not completely constant, but changes from year to year due to changes in the magnetic field of both the Earth and the Sun.
The uncertainty range is +/-40 in remains from the Middle Ages and +/-100 years in remains from the Stone Age.
Fish can also cause errors in age determinations, for example on the remains of settlements from the Stone Age. Namely, fish contain rather little C14, and if the Stone Age people prepared fish in their clay vessels, results could possibly be obtained that were many thousands of years old.
In fact, this was not fully revealed until after a Danish study in 2013, when scientists cooked freshly caught fish in clay pots and then dated them using the C14 method.
The results showed that the freshly caught fish was 2,000 years old, and the pottery itself also looked much older than it actually was.
