Arguably, the first takeaway from studying a county map of the 2012 US presidential election is the significant influence of the USA’s dense urban cities. Over a purely geographical spread, the above map looks more like a landslide for Mitt Romney’s Republican party (red), not a comprehensive 332 – 206 electoral vote victory for the incumbent, President Barack Obama and the Democrats (blue). The high populations and therefore large number of votes from such states as California, Florida, New York, Illinois and Pennsylvania carried the 44th president back to the White House, despite the large swatches of red across such central states as Oklahoma, Utah, and West Virginia.

However, there is another curiosity on the map. In the middle of a sea of red in the southeast of the country, a thin blue line of Democrat voters can be seen curving through such states as Mississippi, Alabama, Georgia, South Carolina and North Carolina. It’s a trend seen not only in 2012, but also 2008, 2004, 2000 and into the last millennium. Why is this narrow band of voters consistently voting Democrat when their surrounding neighbours opt for the Republicans?

The mysterious blue line in the 2012 election counties map (Image: Kelvinsong)

The answer lies in a mix of geology and demographics. Visitors to this region one hundred million years ago (give or take a few million years) would have observed the fractured continental ‘North America’ of the Cretaceous era, divided, as it was then, into the western Laramidia landmass, and the eastern Appalachia landmass. Coastlines sat in very different locations to where they are today, and – crucially – included a large region of coral reefs off the southern edge of Appalachia, around what is now the southern foot of the Appalachian mountains, in Georgia, Alabama and South Carolina. As time passed, the shallow seas in the region dissipated, the landmasses fused into one and the coral reefs crumbled into soil.

Late Cretaceous North America showing the landmasses of Laramidia and Appalachia (Image: Ron Blakey)

Early settlers to the US may not have fully understood this geological history, but they knew fertile land when they found it. The vast organic matter left in the soil from these ancient reefs made for excellent agriculture and, over the course of 19th century, a vast and profitable cotton business grew along this ridge marking the old Appalachian coastline.

Prior to Abraham Lincoln’s preliminary Emancipation Proclamation in 1862, abolishing slavery across the United States, such an industry would have been heavily dependent on African slaves with around four million individuals still enslaved at the passing of the Act. In the century-and-a-half that followed, despite the significant changes in society through time, this same part of the country became the spot with the highest concentrations of African-Americans – descendants and family members of former slaves – situated along the location of the old Appalachian coastline.

Proportion of American population self-describing as ‘black’ in the 2010 census (Image: United States Census Bureau)

Thanks to the policies of 36th president, Lyndon B. Johnson – such as the 1964 Civil Rights Act – the Democratic party has, especially since the 1960s, been the party most closely aligned with African-Americans. Barack Obama collected 93 per cent of all African-American support in the 2012 presidential race, a figure which hasn't fallen below 80 per cent for decades.

Hence, despite their fellow Georgians, Mississippians and Alabamians deciding that Mitt Romney was the best man for the job, the residents of the mysterious blue curve continue to put a cross in the box of the Democrat candidate, an action traceable back to a one hundred million year old coral reef.