Search begins for Ireland's ancient bridge to Britain
By ferry or by aeroplane is the usual way to travel from Ireland to Britain.
But a major geological research project by scientists at the University of Ulster is trying to discover if people could have once walked from one landmass to the other via a land bridge.
The three-year international seabed study will be spearheaded by Professor Andrew Cooper and an expert team of researchers.
The underwater investigation will focus on how far the water level of the Irish Sea fell during the last ice age.
This research, funded by the UK's Natural Environment Research Council, will also aim to determine if the two islands were ever joined by dry land.
Professor Cooper said the sea level was much lower 15,000 years ago when massive glaciers blanketed the Earth.
Water trapped as ice meant the sea level off Ireland's southern coast was 60 metres lower than it is today.
Professor Cooper will be assisted by scientists from Trinity College Dublin, the British and Irish geological surveys, and others from universities in Britain, US and Canada.
The project - costing almost £1m - will assess historical seabeds around the Irish Sea including Bantry Bay, Waterford, Cardigan Bay, Drogheda, Morecambe Bay and Belfast Lough.
"We have chosen these particular sites because they have the highest potential for preserving these types of environment," Professor Cooper said.
"The question of whether Ireland and Britain were ever connected by land has never been answered satisfactorily and there are many competing hypotheses based on everything from the different mammal populations, archaeology, and computer modelling.
"Nobody has ever looked at the geological evidence that is preserved on the sea floor."
Next year the team will go back on a bigger ship and collect sediment from the seabed to help reconstruct the past environment.
Professor Cooper added that discovering whether a land bridge existed was "a bit of a long shot".
"The highest likelihood is if there was (a land bridge), it had to have been in the south."
Other geological discoveries:
In 1928 Arthur Holmes showed how convection currents in the Earth's substratum (now called the mantle) underlying the continents could be the mechanism for continental drift.
In 2008 three Australian scientists discovered an ancient reef in the South Australian outback, in an area once covered in water.