In prehistoric times Staffa was covered by the ice sheets which spread from Scotland out into the Atlantic Ocean beyond the Outer Hebrides. After the last retreat of the ice around 20,000 years ago, sea levels were up to 125 metres (410 ft) lower than at present. Although the isostatic rise of land makes estimating post-glacial coastlines a complex task, around 14,000 years ago it is likely that Staffa was part of a larger island, just off the coast of mainland Scotland, which would have included what are now Mull, Iona and the Treshnish Isles.[9]