Established in 2012, and led by Professor Andy Herries, the Australian Archaeomagnetism Laboratory specialises in research that seeks to uncover our human origins.
“Our purpose-built facility is designed for work on archaeological and fossil bearing sites, as part of the development of archaeological science, archaeometry and geoarchaeological research and teaching at La Trobe,” explains Professor Herries.
The laboratory also works on mediaeval, chrarcolithic, bronze age and historical period sites in Australia, China, Kenya, Oman, Saudi Arabia and South Africa.
We asked Professor Herries about the discoveries that were made possible by this world-class facility.
Dating the Oldowan
The Oldowan is the first definitive stone tool technology used by humans, first occurring between around 2.6 million years ago (Ma). Recent work by Professor Herries on the Homa Peninsula in southwest Kenya has pushed back the origins of this technology to between 3.03 and 2.61 Ma, but closer to 3.03 Ma.
This work also dated fossils of the early human species Paranthropus, the first known from this region, and some of the earliest ever discovered. This work was recently published in Science and will form the basis of a much wider study of the age of sediments, archaeology and hominin fossils in this region of Kenya.
At around 1.8 Ma, a transition occurred to Acheulian technology, characterised by the emergence of hand axes and associated with the first definitive species of our genus Homo, Homo erectus. Our understanding of this transition is limited, but a series of new archaeological sites at Kilombe Caldera in Kenya (pictured above) are helping us to answer this question.
Our team has been involved in dating the Kilombe Caldera with Oldowan bearing layers at ~1.78 Ma, just prior to the first occurrence of Acheulian in the sequence. This makes the Acheulian at Kilombe potentially some of the earliest in the region.
The first samples were run by Hayley Murphy, an undergraduate Archaeology student who was completing an internship subject in the laboratory. She analysed volcanic tuffs from within the Caldera below and above the Oldowan levels and established that the Oldowan stone tools were deposited at the end of a reversal in the Earth's magnetic field at 1.78 Ma.
The rest of the sequence is now being analysed by PhD candidate, Elizabeth Topping.
Dating the world's oldest Homo erectus
Drimolen is a cave in South Africa that has yielded the most complete specimens of the early human species, Paranthropus robustus, a specialist side-branch in our evolution.
In 2015, an undergraduate Archaeology student on the La Trobe Palaeoanthropology Field School at Drimolen found the skull of an early specimen of our own genus, Homo.
Palaeomagnetic analysis, combined with other methods, dated the skull to between ~2.04 and 1.95 Ma. Work by two La Trobe archaeology PhD students confirmed the specimen represented Homo erectus, the ancestor of all later species of Homo, including Homo sapiens, making it the oldest known fossil of Homo erectus ever discovered. This work was published in Science in 2020.
The laboratory has also dated many other well-known early human fossils such as the recently discovered species, Australopithecus sediba and Homo naledi.
Reconstructing the ancient magnetic field of the Earth from burnt archaeological features
Several firebricks were found by a commercial Heritage company in the bottom of a well at an iron foundry in central Melbourne. They were identified as dating between 1842-1864, manufactured in Scotland, and transported to Australia for use in the foundry.
Archaeomagnetic analysis of the bricks indicated that they recorded the intensity of the Earth's magnetic field in Melbourne between 1858-1863. Some bricks also retained the intensity of the Earth's magnetic field from when they were manufactured in Scotland.
This work shows the potential of archaeomagnetism to source fired material imported into Australia, as well as reconstruct the past magnetic field of the Earth using historical archaeological material, even if that material is ex-situ. This method is also regularly used to help understand the association and heating history of Aboriginal Australian campfires and heat retainer technology.
Reconstructing past environments from archaeological caves
The input of iron minerals in cave sediments is controlled by the source of the rock from which they are derived as well as local soil forming conditions, temperature and rainfall.
During warm interglacial periods, warm, wet climates create large amounts of strong iron mineral phases such as magnetite. During cold, glacial periods the formation of these strong iron phases is less, and sediments can be dominated by rock fall from the cave walls.
By identifying the magnetic minerals present in archaeological cave sequences, their concentration and grain size, these climate shifts between warm and cold phases can be identified across a wide range of environments. This type of analysis can also be used to identify fire use in archaeological cave sites.
Our team has undertaken this type of research on a range of sites in Australia and Africa. In the Pilbara region of Western Australia, it has shown the relationship between climate shifts and occupation intensity for sites stretching back 42,000 years, while in Kenya, the site of Panga Ya Saidi has been used to identify climatic shifts over the last ~78,000 years. At Pinnacle Point in South Africa this type of work has also been used to map 74,000 year old fireplaces in situ using high-resolution analysis, and even create 3D maps of fire and site use through time.
At Panga Ya Saidi environmental magnetism was used to identify and correlate the oldest known occurrence of Later Stone Age technology, consisting of micoliths, to a distinct cold glacial period around 63,000 years ago.
Research is ongoing in the Pilbara region, with work being undertaken by undergraduate students as part of an Archaeology internship subject.