 During the last glacial period , and up until about 9000 years ago , most of Ireland was covered with ice , most of the time . Sea levels were lower and Ireland , like Great Britain , formed part of continental Europe . By 12 @,@ 000 BC , rising sea levels due to ice melting caused Ireland to become separated from Great Britain . Later , around <unk> BC , Great Britain itself became separated from continental Europe . The earliest evidence of human presence in Ireland is dated at 10 @,@ 500 BC . Until recently the earliest evidence of humans in Ireland were Mesolithic people who arrived by boat from Britain between 8000 BC and 7000 BC . 
