It is subtle, and it blends in well with the surroundings, and if you are not looking for it there is a good chance you will scan right over it. But once someone points it out on a true-color map, it is impossible to unsee: a crescent of off-hue land in Mississippi and Alabama that is so perfectly-arced it looks unnatural.

It is like a giant, state-size UFO came skidding to a halt in the Deep South and then picked up and left again. Or as if the Appalachian Mountains were actually a massive river, and this crescent was its delta.

In reality, this arc is super-fertile, cultivated land surrounded by dense forest. It is the shoreline of the Gulf of Mexico as it existed 145 million years ago.


During the Cretaceous Period, the shoreline in North America looked something like this map (below) from the U.S. Geological Survey.

Over millions of years, as ocean critters died, their little shells fell to the floor of the then-Gulf. After the water receded, the remnant exoskeletons turned into land that is packed with calcium. Calcium is great for plants not only because it is a nutrient, but it also helps the soil maintain moisture balance and the correct salinity and acidity.

A map of the Southeast U.S. indicating where the shoreline used to be about 145 million years ago during the Cretaceous Period. The region in yellow is where the ocean would have reached. (USGS)

The region, “Black Belt,” was originally named for the color of the soil — a dark, rich black that indicated high concentrations of carbon nutrients.

That is how Booker T. Washington described it, noting that because of the fertile soil and the desire to plant, grow and harvest there, it was also “the part of the South where the slaves were most profitable, and consequently they were taken there in the largest numbers,” he wrote in his autobiography. “Later and especially since the war, the term seems to be used wholly in a political sense — that is, to designate the counties where the black people outnumber the white.”

It is the earlier, biological definition that the geographical Black Belt Prairie stems from.

“One visiting the Black Belt today would likely see lots of agricultural fields filled with corn, cotton, and soybeans, as well as cattle production,” said JoVonn Hill of Mississippi State University, who studies Southeast biodiversity.

Black Belt Prairie used to comprise 356,000 acres of open prairie, according to Hill, who spoke with NASA Earth Observatory.

“Estimates suggest that less than 1 percent of these prairies remain today,” NASA EO reports. “Find a remnant of the Black Belt prairie, Hill notes, and you could see some of its unique grassland birds; more than 200 species of plants, 1,000 species of moths, 107 species of bees, 33 species of grasshoppers and 53 species of ants.”