Last month, many around the world read about the unveiling of the remarkably intact remains of two Australopithecus sediba individuals from the Malapa cave site in South Africa.
What these remains mean for the way we draw our family tree – are they or aren’t they our direct ancestors, for instance – is still being debated.
The new method is based on the fact that over the past 60 years, environmental levels of radiocarbon have been significantly perturbed by mid-20th-century episodes of above-ground nuclear weapons testing.
Before the nuclear age, the amount of radiocarbon in the environment varied little in the span of a century.
Over the past six decades, the amount of radiocarbon in people or their remains depends heavily on when they were born or, more precisely, when their tissues were formed.
Forensic anthropologists at The University of Arizona took advantage of this fact in a recent study funded by NIJ.
We don’t really know why it happens, or even when it is likely to happen next, but every several hundred thousand years or so, the Earth’s magnetic field reverses. We know this, because when rocks are formed, they are indelibly marked with the normal or reverse polarity of their birth time, or chron.
So, if you know the radioactive isotope found in a substance and the isotope's half-life, you can calculate the age of the substance. Well, a simple explanation is that it is the time required for a quantity to fall to half of its starting value.
So, you might say that the 'full-life' of a radioactive isotope ends when it has given off all of its radiation and reaches a point of being non-radioactive.
The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. This process by which an unstable atomic nucleus loses energy by releasing radiation is called radioactive decay.
The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life.
Then there was Lucy, a fossil remain from the pre-Homo hominid Austraopithecus afarensis.