Presentation on theme: "Learning Goals Students will: 1) Be introduced to the field of Geology and understand the basic history of the science. 2) Understand methods of dating."— Presentation transcript:
Learning Goals Students will: 1) Be introduced to the field of Geology and understand the basic history of the science. 2) Understand methods of dating rock strata (layers) 3) Have the background for understanding the geological history of the planet.
Success Criteria Students will: 1) Be able to name the founding scientists in the field of Geology and name their contributions. 2) Distinguish the difference between relative and absolute dating 3) Apply the rules of Radiometric age dating to date sample rocks (carbon-14, 238 U/ 206 Pb)
The 17 th Century – The Age of the Earth The general belief of Europeans of the Judeo-Christian tradition was that the Creation stories of the bible were absolute truth. Creationist believe that by studying nature, God’s plan would be revealed. In 1625, Archbishop James Ussher (Primate of all Ireland) used the book of Genesis to determine the age of the Earth. He concluded that the Earth was created on exactly October 23, 4004 B.C. meaning that the Earth was approximately 6000 years old. This value carried great weight for centuries and is still quoted by Creationists today. James Ussher (1581–1656) Anglican Archbishop of Armagh and Primate of All Ireland between 1625–1656.
Historical Background Modern Geology made great strides in its development in the 17 th century. In the 17 th century, Geology became its own science in the world of Natural Science. To prove the Bible’s authenticity, individuals felt the need to demonstrate with scientific evidence that the Great Flood (The Story of Noah’s Ark in Genesis) had in fact occurred. Early Geologists began to increase observations of the Earth’s composition, which in turn led to the discovery of fossils.
Strata and Steno During the 17th century the heated debate between religion and science over the Earth’s origin further propelled interest in the Earth and brought about more systematic identification techniques of the Earth’s strata (layers). The Earth’s strata can be defined as horizontal layers of rock having approximately the same composition throughout. An important pioneer in the science was Nicolas Steno. Steno was trained in the classical texts on science; however, by 1659 he seriously questioned accepted knowledge of the natural world.
Geology – the new Science The term "geology" was first used in publications by two Swiss naturalists, Jean-André Deluc and Horace-Bénédict de Saussure Once the term was established to denote the study of the Earth and its history, geology slowly became more generally recognized as a distinct science that could be taught as a field of study at educational institutions.
Economic Geology In the 18 th century it was realized that a careful study of the Earth and its materials could help people locate important minerals (metals, semi-precious stones etc.) and locate and exploit them. in 1774, Abraham Werner published the book On the External Characters of Minerals, which brought him widespread recognition because he presented a detailed system for identifying specific minerals based on external characteristics (Mineralogy). The more easily minerals could be identified and found, the more money could be made. This drive for economic gain propelled geology to the forefront and made it a more popular subject to pursue.
Neptunists and Plutonists In the 18 th century the influence of Chemistry on science was becoming very important. Werner believed that minerals were deposited by water (he was correct in many cases) and that even Basalt and Granite crust were precipitated from water. Werner’s system was influential and those who accepted his theory were known as Diluvianists or Neptunists. The Neptunist thesis was the most popular during the late 18 th century, especially for those who were chemically trained. However, another idea slowly gained strength in the 1780’s. Instead of water, some mid eighteenth-century naturalists such as Buffon had suggested that strata had been formed through heat (or fire).
Neptunists and Plutonists This thesis was modified and expanded by the Scottish naturalist James Hutton during the 1780s. He argued against the theory of Neptunism, proposing instead the theory of based on heat. Those who followed this thesis during the early nineteenth century referred to this view as Plutonism : the formation of the Earth through the gradual solidification of a molten mass at a slow rate. These same processes that had occurred throughout history and continued in the present day. Many of these volcanic features could not be explained by Neptunists.
Neptunists and Plutonists This led him to the conclusion that the Earth was immeasurably old and could NOT possibly be explained within the time lines inferred from the Bible. Plutonists believed that volcanic processes were the chief agent in rock formation, not water from a Great Flood.
The Stratigraphic Column In early 19th century the mining industry and the Industrial Revolution encouraged the rapid development of geology and interest in the stratigraphic column - “the sequence of rock formations arranged according to their order of formation in time.” It was during this period that British geologists named specific sequences of rock the Cambrian (after Wales), the Ordivician, the Silurian and the Devonian. 1739 Topographic Map of the Dolomites: by Gregorio Piccoli del Faggiol
William Smith and the first Geological Map In the 1790’s, the mining surveyor William Smith travelled the country working on the canal system and produced the first geological map of Britain. Smith found empirical evidence that fossils were a highly effective means of distinguishing between otherwise similar formations of the landscape or rock layers (strata) as he travelled the country working on the canal system and produced the first geological map of Britain.
Catastrophism In early 19 th century Britain, the theory of Catastrophism was developed with the aim of reconciling geological science with religious traditions of the biblical Great Flood. In the early 1820’s, English geologists interpreted "diluvial" deposits as the outcome of Noah's flood, but by the end of the decade they revised their opinions in favour of local flood inundations. Charles Lyell challenged Catastrophism with the publication in 1830 of the first volume of his book Principles of Geology which presented a variety of geological evidence from England, France, Italy and Spain to prove Hutton’s ideas of gradualism correct.
Uniformitarianism Hutton and Lyell are considered to be the “fathers” of the field of modern Geology. Lyell argued that most geological change had been very gradual in human history. Lyell provided evidence for Uniformitarianism - a geological doctrine that processes occur at the same rates in the present as they did in the past and account for all of the Earth’s geological features. Lyell’s works were popular and widely read, and the concept of Uniformitarianism took a strong hold in geological and scientific circles. Lyell suggested features such as canyons require millions of years to form
Add Charles Darwin Darwin's discovery of giant fossils helped to establish his reputation as a geologist, and his theorizing about the causes of their extinction led to his theory of evolution by natural selection published in On the Origin of Species in 1859. Darwin’s studies and the work of William Smith suggested that layers of rock were very old and put the sciences of Evolution and Stratigraphy into direct conflict with the church.
The Late 19 th Century In the 19th century, scientists established the age of the Earth in terms of millions of years based on the principals of Uniformitarianism. Such dates could not be reconciled with the dates for the Bible. By the early 20th century, discoveries of radioisotopes and their “radioactivity” (radioactive decay of isotopes) influenced the study of Geology.
Lord Kelvin and the Age of the Earth Perhaps the most renowned scientist of the late 19 th century was William Thompson (1824-1907), better known as Lord Kelvin. Thompson was born in Ireland but spent most of his life in Scotland. His great achievements in many fields of Physics, most notably Thermodynamics, earned him a knighthood from Queen Victoria (as the 1 st Baron Kelvin). The temperature scale still bears his name.
Lord Kelvin and the Age of the Earth Lord Kelvin challenged early scientific views of the evolutionists and the ages they gave to rock strata. Darwin suggested that chalk deposits were about 300 million years old based on sedimentation rates. Kelvin was skeptical (of Biological theories) and wanted to apply the hard science of Thermodynamics as proof. Others scientists suggested values for the Age of the Earth in the billions and still others suggested that the Earth had always existed – a uniformitarian idea that even Einstein suggested about the universe.
Kelvin & the Age of the Earth Kelvin, whose views held great sway as the President of the Royal Society, used thermodynamics to estimate the age of Earth. His calculations were based on the known size of the Earth and the cooling rate of a molten planet to its present state. Kelvin calculated values between 20 and 400 million years with a likely age of 100 million years. The great error in his conclusion was the result of the fact that he did not know about radioactivity and radioisotopes. He only learned of these studies in his last decade of life. It is know well known that radioactive decay of heavy isotopes such as U-238 provides much of the heat in the core of our planet. Heat produced by the core continues to prevent our planet from rapidly cooling and suggests that the Earth is much older.
Modern Geology and the Development of the Theory of Continental Drift The determined age of the Earth as 2 billion years opened doors for theories of continental movement during this vast amount of time. In 1912, Alfred Wegener proposed the theory of Continental Drift. This theory suggests that the continents were joined together at a certain time in the past and drifted like rafts over the ocean floor, finally reaching their present position.
Theory of Continental Drift The shapes of continents and matching coastline geology between some continents indicated they were once attached together as a supercontinent known as Pangaea. Additionally, the theory of continental drift offered a possible explanation as to the formation of mountains. Unfortunately, Wegener provided no convincing mechanism for this drift, and his ideas were not accepted during his lifetime. Over the past 50 years, evidence collects for the Theory of Continental Drift or Plate Tectonics. This becomes the single most important theory in Geology – a theory upon which all other Geological theories are built.
Radiometric Dating By the mid 20 th century, the Earth’s estimated age was 2 billion years, based on the science of radiometric dating. Radiometric dating determined the age of minerals and rocks, which provided the necessary data to help determine the Earth’s age. With this new discovery based on verifiable scientific data and the possible age of the Earth extending billions of years, the dates of the geological time scale could now be refined.
Radioactive Dating of Extra- Terrestrial Objects The realization that rocks present when the Earth was formed would likely have been eroded or recycled by tectonic processes, Geologists sought to date the Earth by testing extraterrestrial objects such as meteorites. Astronomy and Geology have remained in close partnership over the past few decades.