Around 1200 million years ago, a massive, 100 metre long rock fell off a low cliff and splatted into the mud below. The rock weighed almost 250,000 tonnes and was made of the ancient Lewisian gneiss basement rock that is found in the North West Highlands of Scotland and the Outer Hebrides. Now, more than a billion years later, the rock is back at the surface at Clachtoll, exposed within the lowest layers of the Stoerr Group of the Torridonian.

A recent paper published in Geology by Zachary Killingback and co-authors presents a detailed analysis of the fallen rock, and the network of cracks that formed as a result of the impact. The cracks on the underside of the rock were forcibly filled with slurry as the rock landed in the mud. But cracks on the upper surface were filled more slowly as the fallen rock gradually got buried in sand.

Zach Killingback carried out this research as a Masters student at the University of Durham. He has autism, and an article describing the research in National Geographic explores some of the challenges of geological fieldwork and research.