What the Muck of Walden Pond Tells Us About Our Planet
'In 1845, Henry David Thoreau repaired to a cabin in the woods beside Walden Pond “to front only the essential facts of life, and see if I could not learn what it had to teach.” During the last two years, my students and I have come to that same pond to see what we could learn from the sediments beneath it.
In “Walden,” Thoreau wished for a fanciful “realometer” to cut through the “slush of opinion, and prejudice and tradition … to a hard bottom.” My own realometers are made of soft lake mud. One of the things I’ve reaffirmed for myself in this endeavor is that there is no such thing as a post-truth world, despite recent declarations to the contrary. Empirical facts are true whether people accept them or not, and science offers our clearest view of them.
Walden is a kettle pond, a 62-acre dimple in sand and gravel that formed around a block of melting glacial ice about 15,000 years ago. It was here that Thoreau produced one of the first maps of an American lake bed by lowering a weighted line through winter ice. He measured a depth of 102 feet in the western basin, demonstrating that the pond was not bottomless, as local residents had claimed. (In fact, it is one of the deepest in Massachusetts.) Thoreau also recognized that Walden could be both a window and a mirror. He called it “Earth’s eye,” in which we can see ourselves and our world reflected.
When I stand on the water’s edge, I look past the ripples and reflections and consider what lies beneath them. The bottom is a time capsule. Within its sediments are layer upon layer of fine silt washed in from the shore, golden pollen grains from flowers and trees, charcoal from forest fires, insect wings, fungus spores and the remains of microscopic algae. Echo soundings of the deep basin by the Salem State University geologist Brad Hubeny and colleagues recently revealed about 30 feet of mud dating from the birth of the pond.
In 2015, two students and I lowered weighted plastic tubes through 45 feet of water near the center of the pond and hauled up several sediment cores. The longest measured two feet, enough to capture 1,500 years of environmental history. I can now read the pond’s story in the muck as if I were reading pages in a book.'>>>
http://www.nytimes.com/2017/01/07/opinion/sunday/what-the-muck-of-walden-pond-tells-us-about-our-planet.html?
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