Half a million years ago some of our early human ancestors were living on the edge of the South Downs.
Until very recently, fossil bone fragments unearthed by archaeologists working in a small chalk quarry in Sussex were believed to be the oldest evidence of human-like species to be found in Britain.
‘Boxgrove Man’, a hunter-gatherer, lived around 500,000 years ago on the coast during one of the warm interludes in the Ice Age. His ancestors would probably have migrated to Britain from Europe by walking across the dry floor of the English Channel.
Much later, around 6,000 years ago in the late Stone Age, modern humans started to settle the chalklands and clear the extensive forests that once covered the Downs.
Recent finds of early Stone Age flint tools in river deposits exposed in Norfolk’s coastal cliffs suggest our ancestors were here as early as 800,000 years ago. They appear to have lived beside a large, slow flowing river, with forests nearby.
Folding and uplifting
In the same phase that created the Alps, the effect rippled out towards south east England. Massive thick layers of chalk rock were gently folded and uplifted. The rocks were stretched at the peak of the fold, and these weakened rocks were easily eroded.
The erosion left the North Downs on one side and the South Downs as separate remnants on the other side, each with a steep slope (escarpment) facing inwards and a gentle, rounded back slope or ‘down’.
Chalk is porous and so normally water drains into the rocks and emerges as springs further down. In the Ice Age, under tundra conditions like Alaska today, the pores were blocked by frozen water. So when melting occurred in the top layers, the water - together with a sludge of soil and chalky debris - was forced to flow over the land.
This is how the valleys were carved into the chalk, including the row of steep short valleys in the Downs escarpment in the main photograph. When the ice in the rock finally melted, the streams once more disappeared underground, leaving ‘dry’ valleys.