During the last glacial period, and up until about 12,000 years ago, most of Ireland was covered in ice, most of the time. Sea levels were lower and Ireland, like Great Britain, formed part of continental Europe.
By 16,000 BC, rising sea levels due to ice melting caused Ireland to become separated from Great Britain.
Later, around 6000 BC, Great Britain itself became separated from continental Europe. The earliest evidence of human presence in Ireland is dated at 10,500 BC, demonstrated by a butchered bear bone found in a cave in County Clare. It is not until about 8000 BC, however, that more sustained occupation of the island has been shown, with evidence for Mesolithic communities around the island. These Mesolithic communities lived as hunter-gatherers across the island until about 4000 BC.