Globally significant volcanic event formed Giant’s Causeway, scientists findtheguardian.comGeochronologists say Antrim coastline’s basalt columns developed over 5.5m years – 8m less than thoughtGlobally significant volcanic event formed Giant’s Causeway, scientists findtheguardian.comGeochronologists say Antrim coastline’s basalt columns developed over 5.5m years – 8m less than thought