Then he examined layers of sediment in these deep cores, using a suite of techniques to calculate the age of the sand, other rocks, and organic matter in each layer. (uvm.edu)
The team found layers of sediment and rocks that built up over time, recording the flow of the ice sheet and reflecting climate change. (sciencedaily.com)
These clues turned up throughout the million - year - old layer of sediment, indicating that fires had burned repeatedly at the site. (discovermagazine.com)