Evidence For A Contracting Earth

By the late 1800s, many scientists had started explaining the origins of Earth's surface features by using the principles of uniformi-

tarianism. While many had no problem accepting the idea of small changes, a large number of geologists still thought that large-scale geologic features, like oceans, continents, and mountain chains, could only be formed by large catastrophic events.

One of the geologists working on the problem was an American named James Dana. Dana was a professor at Yale University and one of the most highly regarded scientists during the late 1800s. Like many geologists of his day, Dana believed that Earth had formed from a large molten ball that had been slowly cooling over time. He also believed that the inside of the planet was still filled with hot magma which produced volcanoes, but the magma that had flowed out onto the surface to become lava had cooled enough to make a solid rock crust.

Based on the work of other scientists, Dana knew that when matter cooled, it also contracted, or shrank in size. Using this information, Dana proposed the idea that, over time, Earth must have become smaller as it cooled. During this contraction, large wrinkles formed on its surface and caused large cracks. These cracks in turn gave the continents their present-day shapes and also produced all of the large mountain chains found on the planet.

At about the same time in Europe, another group of geologists were also looking at this idea of a contracting Earth to explain the shape of the continents. In Austria, a geologist named Eduard Suess came up with a theory that was similar to Dana's but did not follow the principles of uniformitarianism.

Like Dana, Suess also believed that Earth had cooled over time and was slowly contracting. He believed that the oceans were created when large chunks of the crust sank down into planet. The continents were simply those leftover pieces that remained on top. In addition, Suess believed that this sinking action happened in several sudden catastrophic jolts and were not the result of a slow, steady motion.

As it turned out, the theories of both Suess and Dana were wrong for one simple reason: Earth is not contracting. In fact, as far as we can tell, it has stayed pretty much the same size since it first formed. The important point about these early theories is that they showed that scientists were beginning to realize that the entire surface of Earth was not static, but had changed over time.

Figure 2.3 The Krafla area in Iceland, which still shows some volcanic activity, has cracks that run through it. James Dana and other geologists in the late 1800s thought cracks like this were proof that the Earth was contracting, but we now know that features like this are caused by the slow shifting of tectonic plates.

Figure 2.3 The Krafla area in Iceland, which still shows some volcanic activity, has cracks that run through it. James Dana and other geologists in the late 1800s thought cracks like this were proof that the Earth was contracting, but we now know that features like this are caused by the slow shifting of tectonic plates.

Eduard suess names Gondwanaland

Eduard Suess was born in London in 1831. As a youngster, he and his family moved to Austria. After completing his degree in geology, he went to work at the Hofmuseum in Vienna, where he spent much of his time studying and classifying the fossils of ancient sea creatures. In 1857, he wrote a small book on the origin of the Alps, and in the same year he began working as a professor of geology at the University of Vienna.

Over the next 40 years, Suess worked on his theory of the contracting Earth. Even though his ideas would later be proven wrong, he gave the world an important name: Gondwana. According to Suess, Gondwana was a giant landmass that had existed in the Southern Hemisphere and included India, Africa, Australia, South America, and Antarctica. While his ideas about how these continents formed were wrong, the name Gondwana has stuck. It is used by geologists today to describe a giant "supercontinent" that broke apart to form these smaller continents and is a major part of modern plate tectonic theory.

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