The Giddiness of Time

As a geogeek who sees the world through obsidian-tinted lenses, I have long been interested in time, particularly what John McPhee called the deep time of our planetary past. Stretching back 4.54 billion years, that great abyss of eons is why the world looks as it does. Deep time is what makes possible the ever-so-slow diving of the Juan de Fuca Plate under North America, which gives the PNW our dynamic landscape. Deep time is what allowed microscopic organisms to evolve into the myriad of species that grace, have graced, and will grace our little planet. Deep time is what allows me to type this newsletter using minerals that formed millions of years ago. 

Although deep time manifests itself in many ways, it resonates more strongly in some locations. One such place is in downtown Seattle at the southwest corner of 2nd Avenue and Marion Street. There you will find a rather lovely art deco structure, the Exchange Building, originally built to house the city’s commodity exchanges. Alas, it opened in 1930 and the Depression prevented the building from meeting the owners’ great expectations. (Talk about bad timing!) But they did choose wisely with their building stone, the Morton Gneiss of Minnesota.

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With its swirly pink and black layers, the Morton has a dynamic feel, as if the rock was still forming. In one panel rafts of jet black basalt sit like islands awash in a sea of pink. Other building panels look like photographs of blood streaming through arteries, a texture that quarry workers called veiny. But the dominant pattern resembles what would happen if you took a series of photos while stirring together cans of pink and black paint, known as flurry in the lingua franca of stone.

More germane to my interests, the Morton Gneiss is 3,524,000,000 years old, or some serious deep time. As John Playfair wrote in the 18th century “the mind seemed to grow giddy by looking so far into the abyss of time.” The rock is so old that when it formed Earth didn’t look anything like it does now. The oldest evidence for life is also about 3.5 billion years ago, which means that the surface of the planet back then lacked any of the plants or animals or other life forms that provide the colors and textures and chaos we know today. Instead, the surface was probably fairly muted in palette except for the shades of water and lava. Nor, as I noted two weeks ago, were there any of the sounds that began to come into existence relatively recently. 

3.5 billion years ago is so deep in time that the planet may not have functioned as it does at present. The basic way geology works, as has been taught for fifty years or so, is plate tectonics, that the surface of the Earth consists of slabs, or plates, in constant motion. Their jostling is responsible for earthquakes, volcanoes, and all the major planetary processes. But one question remains: When did plate tectonics begin? The answer ranges from one billion years ago to three billion or earlier. In other words, the geological processes that formed the Morton Gneiss may or may not have been ones that operate at present, which I think it PDN, or pretty darned nifty.

Whenever I lead building stone tours in downtown Seattle, I always stop by the Exchange Building. I tell people that the Morton Gneiss is most likely the oldest rock they will ever see. (I know it’s the oldest I will ever see because the older rocks are a long way from anywhere in the Northwest Territories.) I also urge them to touch the Morton Gneiss, to reach back, back, back to the early days of Earth and to bond with the deep time that binds us all together.

My first two tours with the Field Trip Society sold out so we added two more. 

Stories in Stone – June 11 – 2pm – Field Trip Society – My downtown walk exploring building stone, including the Morton Gneiss.

Too High and Too Steep – 1pm – Field Trip Society – We’ll look at the Denny Regrade and the often overlooked but still existing evidence of the topographic changes.

I have been meaning to recommend a couple of newsletters I read. Here they are.

Finding Words – A kindred spirit, David Lukas has a deep love for language and nature and weaves them together weekly. Check out this one on Lewis and Clark.

Taking Bearings – Adam Sowards’s thoughtful take on history and place. This one looks at the Centennial Trail, also a special spot for me. 

Southwest Wawa – I first encountered Owen Lloyd Oliver through his Indigenous Walking Tour of the UW Campus. He continues to be insightful and observant in his writings, including this one about the Super Bowl.

Urban Stalactites

Last week I wrote about looking down. This week I want to write about looking up, though my first example is of looking slightly down and across.

Riding Light Rail the other day, I noticed a curious geological feature at the Tukwila Station. Hanging down from the platform were stalactites, those classic cave structures. The urban ones in Tukwila were a half inch to several inches long and resembled soda straws, another term for them. They are also known as neoformations and calthemites (for the Latin calx, meaning lime; the Latin théma, meaning deposit; and the Latin -ita, a suffix indicting a rock or mineral) and are wide-spread across urban landscapes. 

The key to their formation is the weathering of concrete. As I noted in a previous newsletter about lime kilns, concrete consists of cement (lime) and an aggregate. When water penetrates the concrete and seeps along fractures, it can pick up and carry calcium hydroxide. If the water reaches a surface in contact with air, the calcium hydroxide mixes with atmospheric carbon dioxide and leads to the formation of urban stalactites made of calcium carbonate, also known as the mineral calcite, and by the way, the second ingredient in Tums, after sugar.

For those who are interested, here’s the equation. From Garry K. Smith, Calcite Straw Stalactites Growing from Concrete Structures, one of the best papers on the subject. One point of caution, the solution that forms is very alkaline (pH13) and will burn your eyes or skin.

Water in concrete, particularly where calthemites form, comes from precipitation, gutters that leak, air conditioners, sewer pipes, and the like, says Garry K. Smith, an Australian caver and expert on calthemites. He found that soda straw growth depends on drip rate with maximum growth (2 mm/day) occurring when there are 11 minutes between drips. That growth rate is up to 360 times faster than occurs in caves. The longest calthemites are up to a meter long but most are less than eight inches. Smith told me that if the rate is too fast, on the order of 1 drip/minute, no stalactite forms though a stalagmite may develop below the drip. 

Image also from Garry’s paper, listed above.

Calthemites are quite varied in texture and color, though most are white to taupe. The different hues result from metals encountered by the water during its travels through the concrete. Copper pipes lead to shades of green and blue and iron pipes impart orangish-reds. Halite (table salt) can also affect calthemites but mostly in the surface topography. If left undisturbed, urban stalactites can last forever, says Smith, though they are hollow and could break due to wind or being bumped by a person or beast. He notes that another problem is that the alkaline, or basic, chemistry of the drip can damage car paint, which would probably trigger removal, or at least staunching water movement.

From: Paul L. Boughton, “Morphogenesis and Microstructure of concrete-derived calthemites,” Environmental Earth Science (2020) 79:245.

In Seattle, calthemites form in a variety of locations, including tunnels, overpasses, the undersides of bridges, parking garages, and basements. (With all of the graffiti covering these types of locations, they’re sort of like our own small scale modern Chauvet Cave.) The key, as noted above, is concrete, as well as water. As we Seattleites try to deal with this summer’s heat wave, what could be better than exploring for urban stalactites in a dark place, underground or under a big concrete structure? Have fun.

Calthemites under I-5 where it crosses over Weedin Place. Longest stalactite looks to be about 6-7 inches. 

I would like to thank Garry K. Smith, who provided helpful information and who has written about calthemites here and here

Please let me know if you know of/find any of these splendid little formations.

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