Dating Our Ancestors – Measuring the Age of Australopithecus sediba

Dr Robyn Pickering with the 2 million year old flowstone in the mass spectrometry clean laboratory. Image: Warrick Joe

I’ve just had an article published on Science Alert: Dating Our Ancestors – Measuring the Age of Australopithecus sediba (Science Alert). The article was actually written based on research I conducted for an Up Close podcast on the subject. Check out the podcast here.

And in case you’d prefer to read it here…

Every so often, a curious thing happens to the Earth’s magnetic field. 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. North becomes south; south becomes north. We know this, because when rocks are formed, they are indelibly marked with the normal or reverse polarity of their birth time, or chron.

Apart from being a geological curiosity, the constant toing-and-froing of the Earth’s polarity has proven extraordinarily useful in pin-pointing the geological ages of rocks. This is perhaps no better illustrated than in the recent – and incredibly precise – dating of the Australopithecus sediba remains from South Africa.

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.

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. Then there was Lucy, a fossil remain from the pre-Homo hominid Austraopithecus afarensis. Lucy was found in Ethiopia and dated to 3.2 million years ago.

At the 2 million year mark, the crucial transition point when Australopithecus became Homo, few fossil remains existed. It turns out that the two ill-fated Au. 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. Continue reading “Dating Our Ancestors – Measuring the Age of Australopithecus sediba”