Reconstructing the climate of the past
When we wish to understand the major steps in the innovations our ancestors made 100 000 years ago, we also need to understand what environments these people lived in. How adaptable were humans to environmental change and did climate impacts act as drivers for technological innovation and subsistence adaptations?
The 100 000 - 50 000 time interval, which is the focus of SapienCE research, is within the last glacial period. Nevertheless, the period contained large global changes in climate ranging from a situation close to what we have today and a global deep glacial phase with sea level 80 meters lower than now.
Simulating past climates
While we know the global climate changes reasonably well, less is known about climate changes in local environments. We have, however, methods available to both reconstruct climate and environmental changes from natural deposits where climate sensitive tracers are preserved.
We use computer models to simulate climates at various stages of the period. These models are the same as scientists use to simulate ongoing and future climate change. The simulated climate gives us a regional perspective over the area. For this purpose, we first use simulations of the global climate. These models are quite coarse due to limitations in computer power and do not on their own give us the detailed picture we need to compare with the archaeological material. They provide a climatic framework that is downscaled to finer models tailored for the regional climate of southern Africa. In these simulations, we can get results down to a few km spacing to investigate changes in coastal and inland areas due to major sea level changes and regional shifts in temperature and precipitation. These simulations need excessive computer power and are run on the most powerful computers in the country.
Old layers of dirt
In order to compare the climate from the simulations and verify their accuracy we reconstruct the climate using a wide set of methods. Sediment cores drilled offshore the Blombos, Klipdrift and Klasies River sites contain sediment components transported out from land by rivers mixed with sediments from the ocean. Wetness of the land areas, its vegetation cover and type are inferred by using geochemical analyses on plant remains and minerals. We reconstruct the ambient ocean temperature and its variations by geochemical analyses on small fossil remains. Climate information is also distilled from speleothems (dripstones) recovered from caves near the archaeological sites, dated to the same period as the archaeological evidence. By use of carbonate minerals in the speleothems, we can calculate the temperature history of the time the archaeological sites were occupied by humans and variations in wetness/dryness of the area.
Inside the caves
Shellfish and other fossils allow us to infer what climatic conditions the humans experienced, and the sediments forming the floor on which they lived give us other clues. The seasonal range of temperature at the time and which time of the year the caves were occupied are also calculated from shell material.
All this climatic evidence will be compared with archaeological material to create a history of what environments were like in the area when the exciting phases of human innovations took place and what role climate and environmental change may have played.