Science in the Making
Hutton and the Discovery of ”Deep Time”
Near the town of Jedburgh in Scotland is a curious cliff that reveals vertical layers of rock overlain by horizontal layers. How could such a sequence occurred? In the last decades of the eighteen century, Scotland scientist James Hutton (1726-97), a man who is often called “the father of modern geology,“ studied this remarkable cliff and realized that he was seeing the result of an incredibly long period of geological turmoil.
Knowing what you know about sedimentary rocks, you will realize when you look at this cliff that you are seeing the end product of a long chain of events. First, a series of sedimentary rocks was laid down in the usual horizontal fashion, one flat layer on top of another. Then some tectonic activity disrupted those layers, breaking and folding them until they were tilted nearly vertically. Then, after still more tectonic activity, the rocks found themselves at the bottom of the ocean and another layer of sedimentary rocks formed on top of them. Finally, an episode of uplift and erosion brought the rocks to our view.
Hutton realized that geological forces must bee operating for a very long period of time. Each step of the formation—gradual sedimentation, burial, folding, uplift, more sedimentation, and so on—would require countless generations, based on observations of ongoing geological process. In the words of of nature writer John McPhee, Hutton discovered ”deep time.” In order for a formation like one at Jedburgh to exists, the Earth had to exists not for thousands of years or even hundred of thousands of years, but for many million of years.
Today, we know that the age of the Earth is over 4 billion of years old, and the existence of structures like this is not surprising. At the time of its interpretation by James Hutton, however, the rocks at Jedburgh provided a totally new insight into the inconceivable antiquity of our planet. In the words of Hutton himself, the testimony of the rocks offered ”no vestige of a beginning, no prospect of an end.”
The Interdependence of Earth's Cycles:
Earth's, cycles atmospheric, hydrologic, and the rock cycle as if they were completely independent of each other¦ as if they operated alone in splendid isolation. In fact, each cycle affects and is affected by the others.
The amount of rainfall in a given location will affect the rate of erosion and thus the amount of sediment being deposited in deltas—and therefore the amount of sedimentary rock cycle that forms in that specific area. In the same way the atmospheric and water cycles affect the rock cycle. In the same way, the breakdown of rock is essential to the formation of soils in which plants grow. The presence of plants, in turn affects the absorption of sunlight at the Earth's surface and thus the energy balance that controls the movement of the winds and ocean currents. Thus, although each of the three cycles operates on a different time scale, they constantly influence each other.
Finally, over, hundreds of million of years, the global cycle of plate tectonics, which controls the distributions of the Earth's mountains and oceans, influence all other cycles.
Thinking More About Cycles
Beach Erosion
Something about shorelines appeals to people. Beachfront property is highly valued and over the past 50 years America's prosperity resulted in large–scale development of the Atlantic and Gulf coasts. The result, Americans are now aware of the effects of natural cycles on property values.
Beaches, like any other system in nature, are not static but changes in response to environmental forces. Waves lift sand grains up, carry them around, and despot them somewhere else. Large waves tend to move sand away from a beach and deposit it in offshore bars, while smaller waves tend to move the sand back towards the beach. Thus a seasonal movement of sand occurs on many beaches—offshore in the winter (when storms send in large waves), and onshore during the summer. In addition, waves normally strikes a beach at a slight angle, a phenomenon that moves sand along the beachfront. Large storms may completely destroy beaches and dunes, which are rebuilt farther inland over time. Thus every beach is a dynamic, shifting system. Left to itself a beach will move around in response to the forces of wave and storm.
If the beach were left to itself, this would cause no problems. If, however, waterfront properties worth many millions of dollars are on or near the beaches, such movements have enormous economic consequences for homeowners. Should government use public funds to try to protect such homes? Should the government issue low cost insurance to indemnify the owners for loss? Should insurance be issued to allow people to rebuild beachfront homes after a storm?
