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History of the Discipline: Geology & Paleontgology Nicolaus Steno (Danish, 1638-1687) Nicolas Steno – Danish anatomist and scientist, discovered three major principles of geology: Law of Superposition, Principle of Original Horizontality, and the Law of Lateral Continuity. Steno also showed convincingly that fossils were the remains of once living organisms. Law of Superposition - in an undeformed sequence of sedimentary rocks each bed is older than the one above and younger than the bed below. Principle of Original Horizontality - layers of sediment are generally deposited in a horizontal position. Folding and inclination occur after deposition. Law of Lateral Continuity - layers of sediment initially extend laterally in all directions (laterally continuous). Rocks that are otherwise similar, but now separated by a valley or other erosional feature, can be assumed to be originally continuous. In reality layers of sediment do not extend indefinitely - limits can be recognized and are controlled by the amount and type of sediment available and the size and shape of the sedimentary basin. Giovanni Arduino (Italian, 1713-1795) Classified mountains according to rock type Tertiary – gravel, sand and clay beds alluvium Secondary – layered rocks containing fossils sedimentary Primary – crystalline rocks are the oldest igneous and metamorphic Abraham Werner (German, 1749-1817) Werner devised a new system of classification based on his idea of Neptunism. All rocks were deposited or precipitated from an single universal ocean that covered the earth. Neptunism: all rocks are marine in origin Alluvium – gravel, sand and clay bed Arduino’s Tertiary Mountains Sandstones, shales, coal beds &lava flows Transition rocks– ocean cools and deepens, these rocks contain fossils Arduino’s Secondary Mountains Primitive rocks – formed first from original ocean filled with dissolved minerals Arduino’s Primary Mountains Problems with Neptunism 1. Where did all the water from the vast ocean go? 2. How were lava flows deposited in an ocean? Thus enters a new idea… Plutonism - the primitive rocks originated from heat (or fire), and formed underground rather than in oceans. James Hutton (Scottish, 1726-1797) Sicar Point, Scotland - first described by James Hutton 200 years ago. Lawyer, doctor, scientist, and “gentleman farmer” is often considered to be the father of modern geology. Proponent of a dynamic, cyclic concept of Earth history. Champion of the Plutonist theory that challenged Werner’s concepts. Three major contributions that form the basis of geology. Principle of uniformitarianism (actualism) Hutton explains that the present is the key to the past • The earth is dynamic, so as rocks are eroded and weathered, so are there new rocks are created. • Therefore, the geologic process observe today were at work in the past… even the distant past. HOWEVER – those processes may have happened at different rates or with different intensity than they do now. Significance of Unconformities Siccar Point provided Hutton with insight into the pattern and process of sedimentary deposition. Formulated the idea of conformable versus unconformable strata. Conformable - layers of rock that have been deposited without interruption. Unconformity - represents a long period where deposition ceased, erosion removed previously deposited rocks, and then deposition resumed. In each case uplift and erosion are followed by subsidence and sedimentation. Ultimately Hutton realized unconformities represented “a break in time”. Disconformity Disconformity - type of unconformity in which the beds above and below are parallel. Most common. Angular Unconformity Angular Unconformity tilted or folded sedimentary rocks that are overlain by younger, more flat lying strata. Easiest recognized. Nonconformity Nonconformity - separates older metamorphic or intrusive igneous rocks from younger sedimentary strata. William Smith (English, 1769 – 1839) William Smith – English canal builder. Understood stratigraphy, and used the principle to create the first geologic map of England in 1815. William “Strata” Smith formulated three important principles in historical geology: 1. Principle of fossil succession - Older fossils in lower rocks, younger fossils in upper rocks. 2. Principle of biostratigraphic correlation - rocks containing same fossils formed at the same time 3. Index Fossils provide two kinds of information: • • Whether species existed at same time The order in which species existed Principle of fossil succession: Fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. Holocene Pleistocene Pliocene Miocene Oligocene Eocene Fossil succession of horses Major changes: number of toes decreases as teeth become more complex Index Fossils: • short existence in time • distinctive anatomy • abundant as fossils • wide distribution geographically Microfossils provide the best temporal resolution and make ideal index fossils Spores Diatoms Pollen Radiolarians Foraminifera Dinoflagellates Principle of Biostratigraphic Correlation Using the Principle of Fossil Succession and Index Fossils to correlate strata over large distances Biostratigraphic Correlation Rock columns can be correlated using fossils George Cuvier (French, 1769-1832) • A well respected anatomist and paleontologist who validated Smith's observations on fossil succession. • Developed the idea of catastrophism - the stratigraphic record is punctuated by unconformities. These unconformities represent periods of global catastrophic events in which all life on Earth was wiped out (ie: Noah’s Flood). Opposing view of uniformitarianism. Charles Lyell (English, 1797-1875) Authored Principles of Geology (1830) • Expounded on Hutton’s principles of cross-cutting relationships • Developed concept of relative age dating and sequence of events Principle of Cross-cutting Relationships When faults or magma intrudes, we assume fault or intrusion is younger than the rocks affected. Cross-Cutting Relationship: Dike Cross Cutting: Granitic Intrusion Can apply to structures as well – faulting & unconformities Charles Darwin (English, 1809-1882) • Developed a general theory of evolution to account for fossil succession; proposed natural selection as the mechanism for evolution. • Recognized that fossils recorded the evolution and extinction of life • Reviewed the work of Wallace, who had similar findings on natural selection. • Published Origin of Species (1859) Voyage of the Beagle Darwin’s 5 year trip around the globe on the H.M.S. Beagle (1831-1836) gave him the opportunity to OBSERVE many different types of animals. Observations led to a hypothesis… natural selection. Louis Agassiz (Swiss, 1807-1873) • First to propose that immense ice sheets once covered North America (1840), including an the “Ice Age,” which ended about 8,000 to 10,000 years ago • Studied glacial features, like striations, erratics, and moraines Vertebrate paleontologist; moved to • Controversy… U.S. in 1846; Harvard professor The Bone Wars Othniel C. Marsh (US, 1831-1899) • Professor of paleontology at Yale • Founded Peabody Museum of Natural History • Led famous dinosaur explorations of the western U.S. Well… not really led, but rather paid others to undertake explorations. Edwin D. Cope (US, 1850-1897) • Associated with the Academy of Natural Sciences in Philadelphia and the American Museum of Natural History • Led famous dinosaur explorations of the western U.S. Actually spent a great deal of time in the field himself.