Radioisotope dating audio
In the case of radiocarbon dating, carbon-14 (14C) that is trapped into a biological material upon death decays over time, and predictions can therefore be made about when an organism lived according to the amount of carbon-14 remaining in the sample.In uranium-lead dating, the principal is the same: uranium-238 trapped in rocks during their formation decays to lead-206 (and uranium-235 to lead-207), and measuring these isotopes gives us an idea of the age of the rocks.
Given these findings, the only explanation for the normal-polarity fossil-bearing sediment sandwiched in-between two reverse-polarity flowstones, was for the sediment to have formed during a short period known as the Pre-Olduvai event.One thing that is certain, however, is that the remains fit into a previously rather barren period in the fossil record of early hominids.Before their discovery by paleoanthropologist Lee Berger and his son in 2008, there were fossils of Homo erectus, the earliest known representative of our own genus Homo, which were dated to around 1.9 million years old.“What we need to do is extract the uranium and the lead out of the rocks,” explains Dr Pickering, “then we can measure the amount and the various isotopes of uranium and lead and then put all that back together and calculate the ages.” The uranium-lead dating of the underlying flowstone in 2010 provided an upper age limit of 2 million years.A lower age limit of 1.5 million years was deduced by the presence of particular species of animals at the site.At the 2 million year mark, the crucial transition point when Australopithecus became Homo, few fossil remains existed. sediba individuals found at the Malapa cave site some 60 km northwest of Johannesburg met their demise at almost precisely this time.
In fact, the age estimate for the skeletons is 1.977 years old, give or take 2000 years – a remarkably precise approximation given their antiquity.
sediba is the immediate predecessor to the very first species named Homo. sediba means for the way in which we draw our family tree, precisely dating the fossil remains was a crucial first step.
Citation: Pickering R, Dirks PHGM, Jinnah Z, et al. Australopithecus sediba at 1.977 Ma and Implications for the Origins of the Genus Homo. [DOI:10.1126/science.1203697] [link to abstract: Editor's Note: This feature article was provided by Up Close - an audio talk show of research, opinion and analysis from the University of Melbourne, Australia.
Unlike carbon-14 dating, which measures ages in the tens of thousands of years, uranium-lead dating measures in the millions to billions of years.
In fact, uranium-lead dating was responsible for providing us with one of the first accurate measures of the age of the Earth at over 4.5 billion years. sediba remains at the Malapa site, Robyn Pickering was fine-tuning a technique for her Ph D that would enable uranium-lead dating of much younger rocks than it had previously been used to date.
Meanwhile, Dr Andy Herries, from La Trobe University measured the magnetic polarity of the flowstone as being reversed, and the cement-like sediment within which the skeletons were buried as being normal.