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JUDY WOODRUFF: Now to our NewsHour Shares, something that caught our eye that might be of interest to you, too.
Every winter, millions of tons of salt are spread across the country’s roads and sidewalks. Much of it comes Ohio’s Whiskey Island Salt Mine.
Elizabeth Miller of WVIZ/PBS ideastream in Cleveland reports.
ELIZABETH MILLER: When old man winter rears his icy head, there’s one thing that keeps Ohio from becoming a virtual slip ‘n slide: salt. A natural deicer, over 17 million tons of rock salt was spread over roads and sidewalks in the United States during the particularly fierce winter of 2015.
But where does it all come from? The answer might surprise you.
MAN: Right now, we are in the Whiskey Island Mine, 1,800 feet below Lake Erie. And we are mining salt for the purposes of road deicing. Last year, we mined a little over 3 million tons in a pretty mild winter. In a normal winter, we will do about four million tons a year.
ELIZABETH MILLER: Ohio is one of the top exporters of salt in the country, and it’s actually mined right under our noses in places like Cargill’s Whiskey Island Salt Mine.
The 12-square-mile mine lies just offshore of downtown Cleveland.
MAN: Once we blast the salt out of the ground, we got ahead and scoop it up and put it on the belt lines to be sent to the mill for processing.
ELIZABETH MILLER: A system of conveyor belts and elevators bring the salt to the surface. Left behind are gigantic pillars of salt. These support the weight of the thousands of feet of rock and lake above the mine.
But wait. How did all this salt get here, almost 2,000 feet under Lake Erie? To answer that question, we headed to Cleveland’s Museum of Natural History to talk to expert Harvey Webster.
HARVEY WEBSTER, Cleveland Museum of Natural History: We always think, you know, Cleveland, Ohio, has always been north of the equator. It’s been in a temperate location kind of forever, right? And the answer is no. It turns out that North America, like all the other continents, has moved across the planet.
And at the time of the Silurian, 400 million years ago, Cleveland, Ohio, would have been about 1,000 miles south of the equator, in shallow, tropical conditions.
ELIZABETH MILLER: So, Ohio was tropical, oh, yes, and covered in a shallow sea. And its inhabitants are not the kind of thing you see strolling in downtown Cleveland today.
Eventually, these tropical conditions and some overgrown coral reefs caused the sea to dry up, leaving the salt behind.
HARVEY WEBSTER: It would get saltier and saltier and saltier, until, finally, the salt literally settles right out of that water, and forms rock salt. And this happened thousands, tens of thousands of times, and each time it happened, it would add a new layer to the rock column.
And so, if you went to the Cargill mine, when you look at the walls, you will see these alternating bands. Each one of those layers is like a chapter in the history of the world right here in Cleveland as it existed 400 million years ago.
ELIZABETH MILLER: The salt mine looks like another world, and it really is one. It’s the remains of world that existed long before man. But even if you never get down to the mine, you will still see pieces of this world scattered on icy roads all winter long.
For the PBS NewsHour, I’m Elizabeth Miller in Cleveland, Ohio.