geology

Posted by Ellen

That's me with the chisel in my mouth, some summers ago, during geologic field work in the North Cascades, in the state of Washington. I'm climbing a hill called Lincoln Rock that rears up about twelve hundred feet above the apple orchards along the banks of the Columbia River. We'd been told there were some good garnet coronas up there--garnets with white rings around them---the metamorphic feature I was trying to interpret for my thesis project.

We'd also been told that Lincoln Rock was the one place in the North Cascades where a geologist named Bob Miller--a man who climbed cliffs for fun when he couldn't think of an excuse to climb them for research--fell badly and almost cracked his head open. This was my last day in the field that summer, and though I'd had wonderful fun, I was beginning to shift gears mentally, to look forward to getting back home so I could stop worrying about slipping and falling and leaving five children motherless.

Perhaps because of Bob's misadventure, but surely also because I was old and out of shape, I was by far the slowest climber. While I toiled upward inch by inch in the August sun, the rest of the gang was already lolling about in the shade of an overhang at the top of the hill, eating lunch and making fun of me. As I finally approached the scene of this snapshot, a Ph.D. student named Carlos Zuluaga asked if I wanted my picture taken. Then he suggested I put the chisel in my mouth. It seemed like a good idea at the time, it really did.

Anyway, there were indeed nice-looking garnet coronas all over the hilltop, and Carlos and the others kindly helped me smash them out of the outcroppings. We all made it down safely, with rocks in our backpacks. When I got a look at my Lincoln Rock samples under the microscope, however, I discovered that the garnets were rotten; they'd cooled too slowly after their metamorphic odyssey, and a mineral named chlorite had replaced much of the garnet. My thermodynamic models wouldn't work on rock with rotten garnet, so I put the Lincoln Rock samples in a drawer in the basement of the geology building, and maybe they are still there today.

Fortunately, I had plenty of other samples. And I'd love to be back up there again.....

Posted by Ellen

This now quiet flooded hole in the ground was once part of the world's largest open pit iron mine, near Bob Dylan's boyhood home in Hibbing, Minnesota. One-fourth of all the steel ever made in the United States used iron ore from this one mine. The ore sat here for two billion years unmolested, waiting for oxygen to appear in the atmosphere, for life to appear on the surface of earth, and for that life to evolve sufficiently to dig all the iron out of the earth. The digging took about 50 years.

They don't make these big iron deposits any more. Now that the air has oxygen in it, iron will rust away instead of piling up like grains of sand. There are natural processes nowadays that manage to accumulate some iron despite the atmosphere, but they operate on a much, much smaller scale.

Minnesota's Iron Range is what's called a Banded Iron Formation, a BIF. There are fewer than a dozen large BIFs around the world, in Minnesota, Africa, Russia, Australia, Venezuela, Brazil, and Labrador. They are all at least a billion years old; the biggest ones are around two billion years old.

Two billion years is also the age of some of the oldest life forms preserved in the fossil record, organisms called cyanobacteria, ancestors of modern algae. Vast "mats" of cyanobacteria fossils have been found near Hibbing and near many of the world's other banded iron formations.

Coincidence?

Here's one theory: cyanobacteria, sometimes called blue-green algae, were capable of photosynthesis. Like modern plants, they gave off oxygen, which accumulated in the atmosphere and the ocean. The cyanobacteria lived in the ocean, probably near the surface, and the ocean water contained high concentrations of iron, probably leached from early volcanic rocks. Photosynthesis added oxygen to the ocean, which made the iron precipitate out of solution, sinking to the bottom. The iron sediment piled up, and we got our BIFs.

But there's a catch: cyanobacteria are anoxic organisms, which evolved and apparently thrived in a world without oxygen in the air. Their own behavior--photosynthesis--may have contributed to atmospheric changes that literally poisoned them. In other words, they may have caused their own extinction. It may have been a mass extinction, which could explain the huge mats of fossilized cyanobacteria associated with BIFs.

It's hard to imagine how the cyanobacteria could have avoided their fate; they are single-celled organisms with little more brainpower than some of our contemporary politicians. A few varieties did evolve to survive in anoxic niche environments, such as hot mineral springs, but overall their way of life was unsustainable.

Which raises the obvious question: can we humans do any better? As our way of life leads to changes in the atmosphere, can we evolve to survive on an overheated planet? And/or are we smart enough to control the atmosphere to make it more favorable to survival of our species?

Posted by Ellen

After some of you fussed yesterday about the lack of a story to go with the picture, I've got a story for today--the beginning of a two-part story, in fact. It could be classified as another entry in an irregular series dealing with places I've never been to and probably have no business writing about.

The picture looks down on the harbor of Duluth, Minnesota, in 1905, from a vantage point near the top of the city's new inclined railway. The railway may look like part of the town's extensive industrial infrastructure, but it was actually a people-mover, built by the city in the late ninteenth century at the instigation of real-estate developers who wanted to sell houses high up the hill above downtown. "The Incline" operated for about 50 years, powered by an electric motor at the top and working a little like an elevator, with a dummy-car counterweight on the left track that moved downhill when the passenger car on the right track was pulled uphill.

What I didn't know about Duluth could fill several hard drives. Here's what little I did know: it's Bob Dylan's hometown, and the winters are ridiculously cold. The Dylan factoid is only partly true--yes, he was born in Duluth, but he really grew up a hundred miles north in Hibbing, Minnesota, a mining town that had to relocate itself because the mine got too big. As for the factoid about Duluth winters: yes, of course, they really are brutal, with a spell of forty below or worse most years. But "the Incline" was so steep that snow never piled up too deeply on the tracks, not even during blizzards.

As for the things I  didn't know about Duluth: Number one, around the time of this photo, it was among the wealthiest towns in America, claiming more millionaires per capita than anyplace else. It thrived because of a confluence of geology, geography, and the highest technology of the era.

In the 1870s, northern Minnesota had a gold rush; no commercially significant gold was ever found, but the prospectors did stumble on high-grade iron ore in the hills north of Duluth. They'd discovered Minnesota's Iron Range, one of the largest iron deposits on earth and the subject of tomorrow's part of the story.

By the 1880s, Duluth and the Iron Range were connected by railroad. Ore from the mines was off-loaded from the trains at Duluth onto large ships. The ships would have been stuck forever in Lake Superior, unable to exit, had not construction been completed around that time on the mechanized locks at Sault Ste. Marie, which helped ships to descend the 21 feet between Lake Superior and Lake Huron. The ore ships from Duluth sailed a thousand miles across the Great Lakes to the newly constructed steel mills in Indiana and Pennsylvania and Ohio and New York, where newly invented Hulett machines automatically unloaded the ore from the ships and dumped it into blast furnaces. As soon as the new steel cooled, it was snapped up by new factories assembling cars and tractors and locomotives and wringer washing machines and everything else that used to be made in America.

All cities that boom must implode. (I don't know if that's true, but it sounds about right.) What happened to Duluth was World War II, with its extreme demand for iron ore to build tanks and planes and ships to replace the ones that were being consumed in battle.  The Iron Range couldn't keep up; huge wartime scrap-metal drives were needed to supplement the mines.The track of the inclined railway was itself torn up and sold for scrap. By about 1950, all the good ore in the entire Iron Range had been clawed out of the earth and shipped away through Duluth. The city languished.

Fortunately, scientists at the University of Minnesota had seen this coming and were hard at work on a work-around.  Within a few years they came up with a way of using the Iron Range's low-grade ore, called taconite, Taconite isn't as valuable as the old stuff, and it has to be compete with cheap ore now coming in from places like Brazil, and anyway, most of the old steel mills and factories are no longer operating, but Duluth remains a fairly active port to this day. Last year, it handled 500,000 railroad carloads of taconite. The railroad also brings grain to Duluth from all across the northern Plains, which also gets loaded there onto ships.

But nowadays, more valuable than wheat or taconite to Duluth's economy are tourists. Now that the smoke is gone from the old ore processing works, the city's scenic lakeside setting attracts vacationers interested in all the outdoor activities of the north country: boating, fishing, hunting, snowmobiling, and so on. Along the top of the hill is a string of popular state parks. Even the sand bar that protects the harbor, seen in the distance in the photo, is now a park, and also a seaplane base. Visitors are buying up the old houses on the side of the hill to use as vacation homes.

Somewhere in the city, I can't figure out where, is a trail they've named the Bob Dylan Walking Path. Must be near Highway 61.