In the early part of the 1700s, most of the people who studied the Earth believed that our planet had changed very little over time. They believed that the rocks, mountains, and oceans that they saw had been created at the same time that Earth first formed. Earth itself was thought to be approximately 6,000 years old. However, this age was not based on the work of scientists—it was proposed by religious scholars who based their estimate on the story of Earth's creation as it was described in the Bible. (In fact, back in 1658, Archbishop James Ussher of Ireland calculated that the exact year of creation was 4004 B.C.)
As time went on, people who were looking for places to mine coal and iron realized that these valuable materials could be found
near certain types of rocks. As a result, they turned to "naturalists" to make detailed maps of the local rocks. Naturalists were trained to make careful observations about the world around them, and the more they observed, the more they began to question some of the long-held ideas about Earth.
One of the first ideas that these trained observers began to question was the belief that Earth did not change over time. As they drew up their maps, naturalists often came across fossils of fish and other sea creatures high in the mountains, far from any ocean. The only logical conclusion was that these mountains must have been once covered with a great deal of water sometime in the past. How did the water get there? Where did it all go? It seemed some great changes had taken place.
Religious leaders offered an answer: The Bible tells a famous story about Noah and a great flood that covered the entire Earth. Religious leaders argued that these fossils were left over after the floodwaters went away. The Bible had stories about other catastrophes and many scientists believed that these events caused all of the changes that they saw in the rocks. This idea became known as catastrophism, and it gained a great deal of support. One of the biggest champions of this idea was Georges Cuvier, one of the most famous scientists of his day. There was a problem with this idea, though: Every time observations showed evidence of another change in the rocks, catastrophists would have to come up with another catastrophic event to explain it. As you might imagine, things got pretty messy in a hurry.
UNIFORMITARIANISM: SLOW AND STEADY WINS THE RACE
While catastrophists such as Cuvier attributed the characteristics of rocks to Biblical events, other scientists were looking for another answer to the problem. One of the most influential of them was a Scottish doctor named James Hutton. Even though Hutton was not trained as a naturalist, he owned a farm and loved nature. Much of his farm was covered with large rocks that he carefully studied. Over time, his observations stirred in him a real passion for geology.
In his studies of rocks, Hutton noticed certain patterns that seemed familiar. For example, in sedimentary rocks like sandstone and shale, he observed how each layer of sediment had been deposited on top of another layer of sediment below it. When he took a close look in areas where streams flowed into lakes, he discovered the exact same pattern of sedimentary layers. Hutton concluded that the sedimentary layers he saw in the rock had been created in the same way as the layers of sediment he saw in the lake. In fact, the process was exactly the same. Other naturalists had made the same observations, but Hutton took them one step further.
Hutton calculated how fast sedimentary layers were forming in the lake and realized that it would take years just to get a few inches of sediment to build up. He then began to look at the cliffs in the countryside around where he lived. Some of these cliffs were
While Hutton was a great scientist, it turns out that he was a terrible writer. Even though his books included numerous examples to support his theory, his writing style was so bad that few people could understand what he was trying to say. Fortunately, Hutton had a friend named John Playfair who was a professor of mathematics at Edinburgh University. Playfair was very familiar with Hutton's ideas because the two men frequently discussed them. After Hutton died, Playfair was afraid that his friend's work would be forgotten. Even though he was not a geologist, Playfair understood Hutton's theory well enough to write about it. Unlike Hutton, Playfair was a gifted writer, and in 1802, he published a book titled Illustrations of the Huttonian Theory of the Earth. In this book, Playfair clearly outlined the concept of uniformitarianism. The tide slowly turned as other scientists read Playfair's book and began to accept the idea. The real breakthrough came in the early 1800s when a young geologist named Charles Lyell picked up on the idea and became its new champion.
made of sedimentary rocks that had layers that were hundreds of feet thick. To get this much sediment built up would take a lot of time—not just hundreds or thousands, but millions of years. To Hutton, there was only one answer—Earth had to be much older than 6,000 years.
After making many more detailed observations, Hutton was convinced that he was correct. In 1785, he wrote down his ideas in two papers that were presented to the Royal Society in Edinburgh, Scotland. His central idea was a simple one. Instead of Earth's changes being caused by large, catastrophic events in the past, Hutton proposed that all of the geologic features we see in ancient rocks can be explained by processes that can be observed in action today. "The present is the key to the past" is the saying most often used by geologists to express this idea. These small, steady uniform changes acting over a long period of time were all that were needed to make the large changes that took place in the Earth. This idea became known as the principle of uniformitarianism, one of the most important concepts used in geology today.
As you might expect, when Hutton's papers were finally published in 1788, many of the leading scientists of the time thought he was totally wrong. But while he was strongly criticized and mocked, he refused to back down. In 1795, he published his findings in a two-volume book titled Theory of the Earth, in which he provided dozens of examples to support his ideas. In his discussion of the age of the Earth, he said, "We find no vestige of a beginning—no prospect of an end." In other words, he was suggesting that the age of the Earth was too old even to calculate. This was a major change from what was accepted as truth at the time.
Hutton took a big risk in publishing his book because not only did he go against what most scientists believed, but he was also seen as challenging religious beliefs, too. He would have had to face a great deal of public criticism, but he died in March 1797 before these forces could gather steam.
Sir Charles Lyell's New Ideas about Very Old Rocks
Charles Lyell was born in Scotland in November 1797, eight months after James Hutton had died. The Lyell family was fair ly well off. Charles Senior, Lyell's father, was a lawyer. As young Charles grew up, it was planned that he become a lawyer, too, but he had other ideas.
In 1816, Lyell entered Exeter College, where he showed a real talent for math and science. He became interested in geology after reading Playfair's book and was fascinated with the idea of uniformitarianism.
During the summer of 1817, Lyell attended several lectures given at Oxford University by William Buckland, a geologist who also was a big supporter of Hutton's theory. After Buckland showed Lyell some new, detailed geological maps of England, Lyell decided that geology was going to become his profession. This did not sit well with his father, so Lyell continued to study law while keeping his work in geology in the background. Over the course of the next few years, Charles took many trips around England and Europe and made careful observations of the rocks wherever he went. He completed his law degree in 1822 and began working as a lawyer while continuing to study geology on the side. He joined the newly formed Geological Society of London and became their secretary.
In 1825, Lyell was asked to write an article for the Quarterly Review, a journal that published essays about many topics, including the latest developments in science. Like John Playfair, he was a talented writer and was paid well for his work. By 1827, Lyell gave up his law practice to become a full-time author. He decided his first book would be about geology. Rather than redo what others had done, Lyell wanted to see for himself how different geological principles worked. He set off on a year-long expedition to Europe where he met with local geologists and took extensive field notes. When he returned to London in February 1829, he began work on the book. In July 1830, the first volume of his Principles of Geology was published. It became a big hit.
Lyell's Principles clearly laid out the most up-to-date theories about Earth and gave detailed descriptions of how slow, steady forces acting over time shaped the planet. His examples were so clear that, even though he didn't have a degree in science, he was offered the position of Chair of Geology at King's College in London. In this new position, Lyell gave numerous public lectures on geology. (He
These days, most geologists accept the principle of unifor-matarianism and use it in their work. Most of them also believe that, from time to time, large catastrophes have also occurred—giant earthquakes, tsunamis, volcanic eruptions, and even impacts from extraterrestrial objects, such as asteroids and comets, have all had an impact on Earth. These types of catastrophic events still happen today. However, geologists classify these events as following the general rule of uniformitarianism rather catastrophism. Whereas events such as asteroid impacts cause understandable and predictable effects that follow physical laws, events such as a biblical flood would have been a one-time-only event that left no evidence that it actually occurred. The difference between modern-day catastrophists and those of the past is that even those geologists who acknowledge the Earth-shaping power of catastrophies believe that most of the changes that we see acting on Earth are thought to be due to slow, steady processes acting over time.
even encouraged women to attend the lectures, which was unheard of at the time.) When he was not lecturing, he was writing, revising his original book and publishing two more volumes of his Principles. In 1833, he resigned from King's College to concentrate on his research and writing.
Over the next 40 years, Lyell, accompanied by his wife, Mary Lyell, continued to do field work and update his books. In 1838, he published Elements of Geology, which was the first modern textbook on geology. In 1841, he was knighted.
Even though Hutton was the first one to explain the ideas behind uniformitarianism, it was Lyell's work that finally put to rest the idea of catastrophism and caused scientists to accept the idea that small changes acting over a long time could bring about large changes in the Earth. In his second volume of the Principles, Lyell offered an idea about how different animals and plant species changed over time. Based on his observations of fossils, he concluded that many more species must have lived on Earth in the past. These living things went extinct but were replaced by new species. This idea formed the backbone of Charles Darwin's work on evolution almost 25 years later. Darwin himself gave credit to Lyell for setting the stage for his theory of evolution, but he was not the only scientist to be so influenced. In the early 1900s, a German scientist named Alfred Wegener would use the principle of uniformitarianism to put forth his own theory of how the position of the continents themselves had changed over time. His radical idea would be the first piece placed in the plate tectonic puzzle.
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