Sediments, which can be anything from pieces of rock to pieces of shells and even salts precipitated from shallow seas and lakes, are carried by media like air, water, and ice until insufficient energy for transport allow them to sink and pile up in successive layers. That sentence took a long time to read, but it gives us an inverse model of sedimentation. The last words you read are the mostly recently written. In sedimentary rock layers that have lain undisturbed, the topmost layer is the most recent. We read the history, the story, of rocks from the bottom up. Lowermost layers are oldest. You can see the sequence in canyons cut into sedimentary rocks.
Not all areas are overlain by sediments and sedimentary rocks. Barren igneous rocks cover some volcanic areas, but the same principle applies. Lavas on top are youngest. You can see the sequence in canyons cut into layers of basalt.
In both sedimentary and igneous rock areas we see a multilayer structure reminiscent of a layer cake. Mother Nature (picture her in a baker’s hat) can also make an upside-down cake. Rocks can move, warp, and get overturned by tectonic activity as Earth’s plates shift. In some instances, like those producing overthrust faults, a bottom layer might even move over younger rock layers. That displacement makes reading Earth history a bit complicated with rocks imitating the sentences in these paragraphs: More recently written stuff appears on the bottom. Geologists have identified the vectors and causes of such forces for overturned rock layers.
We have seen such disruptions in human history repeatedly. Shifts in thought occur. What was a philosophy in the deep past comes to the present, forced over more recent thinking. Thus, socialism and capitalism, liberalism and conservatism, absolute and situational morality, and cultural tradition and intellectual rebellion keep changing positions. Like the rock layers, they are easy to document in most instances, but turnovers complicate interpretation.
Now you. Feeling or thinking a little as you once did? Something change? Did some force cause an overturn of the “natural order,” placing an older attitude, feeling, or way of thinking on top of your most recent layer? What produced the force?
Not all areas are overlain by sediments and sedimentary rocks. Barren igneous rocks cover some volcanic areas, but the same principle applies. Lavas on top are youngest. You can see the sequence in canyons cut into layers of basalt.
In both sedimentary and igneous rock areas we see a multilayer structure reminiscent of a layer cake. Mother Nature (picture her in a baker’s hat) can also make an upside-down cake. Rocks can move, warp, and get overturned by tectonic activity as Earth’s plates shift. In some instances, like those producing overthrust faults, a bottom layer might even move over younger rock layers. That displacement makes reading Earth history a bit complicated with rocks imitating the sentences in these paragraphs: More recently written stuff appears on the bottom. Geologists have identified the vectors and causes of such forces for overturned rock layers.
We have seen such disruptions in human history repeatedly. Shifts in thought occur. What was a philosophy in the deep past comes to the present, forced over more recent thinking. Thus, socialism and capitalism, liberalism and conservatism, absolute and situational morality, and cultural tradition and intellectual rebellion keep changing positions. Like the rock layers, they are easy to document in most instances, but turnovers complicate interpretation.
Now you. Feeling or thinking a little as you once did? Something change? Did some force cause an overturn of the “natural order,” placing an older attitude, feeling, or way of thinking on top of your most recent layer? What produced the force?
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