A major issue discussed during the workshop on the "Oldest Ice Core Reconnaissance" is the basal layer in an ice sheet, i.e. about 10-20% of the ice thickness, which used to be called the "echo-free zone". It can now be imaged with modern radars, but its formation is not understood at all. Physical processes on the microstructure are the most important factor. And getting those right is the most important thing for the ice-core community in regard of retrieving ice older than 1 Ma.