By REID FORGRAVE - THE NEW YORK TIMES MAGAZINE - OCT. 12, 2017

Minnesota is home to some of the world’s most ancient rocks, as old as 3.5 billion years. Earth has been around for only 4.5 billion years. About 2.7 billion years ago, basalt lava flowed underwater near what’s now the state’s border with Canada; the lava hardened, and the creep of geologic time turned it into a bedrock of greenstone and granite. On top of it, a layer of sedimentary rock rich in iron ore formed nearly two million years ago, when the region was ocean floor. Then a billion years ago, Earth’s crust cracked open, producing a 50-mile-wide fissure stretching from Lake Superior to Kansas. For the next 100 million years, lava bubbled up into what geologists call the Midcontinent Rift, forming a mineral deposit filled with copper and nickel. Settlers first made their way to the area in 1865 in a fruitless search for gold. What they did find was iron ore, and lots of it. Rails were laid for iron-ore transport, and the town of Ely was founded a few years later, in 1888.