Laurentia: the ancient core of North America
Laurentia was an ancient continent whose core forms much of modern North America. Its history also includes Greenland and parts of present-day Scotland. Geological ancestry cannot be read directly from today's national borders or oceans.
See Laurentia 450 million years ago, when its location and neighbours were different from today's. Its name resembles Laurasia, but means something else. Laurentia helped assemble later, larger continental groupings.
A continent has a core and growing margins
An ancient core, or craton, can survive repeated episodes of assembly and breakup. Meanwhile, islands, sediments and other crustal fragments join its margins. Laurentia should therefore not be drawn simply as the completed outline of modern North America moved into the past.
The British Geological Survey describes connections between Scottish rocks and ancient Laurentia. Rocks now on the European side of the Atlantic can have North American geological neighbours. The ocean is younger than some of those connections.
Iapetus separated future neighbours
During the early Palaeozoic, the Iapetus Ocean separated Laurentia from other landmasses. In the BGS account of southern Scotland, Laurentian regions occupied low latitudes while Avalonia began its journey much farther south.
Ocean closure did not mean draining away the water. Oceanic crust was consumed at subduction zones, where one plate descends beneath another. Landmasses approached each other, and eventual collisions deformed their margins. Rocks preserve traces of an ocean that no longer appears in a modern atlas.
From Laurentia to Laurussia
Joining with Baltica and Avalonia produced the larger assembly called Laurussia. Torsvik and Cocks (2005) discuss these connections. Previously independent landmasses became parts of a new whole without losing all their geological differences.
Laurasia is a different, later concept associated with northern Pangaea. Think of the names as chapters in the history of changing connections, rather than three spellings of one continent.
Following the history on a map
Move back to Rodinia, then return to Palaeozoic Laurentia. Large group labels appear only within selected time intervals. Their disappearance does not mean that the ancient core physically ceased to exist.
The model of Cao and colleagues (2024) represents crustal blocks, not the exact outlines of exposed islands and seas. Today's North American colour helps track material. It does not prove that every similarly coloured piece belonged to one continent in every period.