Method of dating fossils
In analyzing the other fossils found around the newly discovered hominid bones.
Many fossils of the other creatures, such as ancient elephants and rhinos, have been dated before at other locations using the volcanic ash, potassium-argon method described above.
A dating method used by Richard Bailey at Oxford University measures the amounts of radiation absorbed by sand grains in and around a bone specimen by measuring radioactive isotopes in the sand and comparing that to a sophisticated radiation transport model using data from a CT scan of the specimens.
The age of the specimen is determined by calculating the yearly rate at which radiation had been absorbed by the sand grains.
This method dates objects by measuring the periodic reversals of the north and south magnetic poles, which have occurred at known times and rates.
Carbon-14 has a half-life of 5,730 ± 40 years, meaning that every 5,700 years or so the object loses half its carbon-14.