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A Short History of Historical Geology I I - Cuvier to Darwin Georges Cuvier (1769-1832) Extinction and Fossil Vertebrates • French comparative zoologist • Expert on vertebrate skeletons • Studied vertebrate remains being excavated from secondary and tertiary strata in the Paris Basin. • Proved extinction by comparing fossil and modern elephants • Published “Discourse on the revolutions of the surface of the globe” describing a succession of prehistoric worlds populated by extinct species. "Such is the economy of nature, that in no instance can be produced her having permitted any race of her animals to become extinct." Thomas Jefferson collected fossils found in Virginia and Kentucky, in part to prove that the Americas hosted animals as impressive as anywhere else in the world. Giant Ground Sloth Jefferson assumed that these animals would be found alive elsewhere on the continent - he did not accept the possibility of extinction. Contrary to Jefferson, Cuvier proved that some species were now extinct by comparing fossil mammoth bones found in Europe with modern elephant bones. Mammoth Elephant American Mastodon Reconstructed by Cuvier Cuvier showed that the bones of animals being found in the Secondary strata were from giant marine reptiles. Mosasaur jaw being excavated from the chalk at Maestricht, Late 1700’s. Mosasaur skull circa 1790 circa 1870 British Isles post-Diluvial Diluvial Tertiary Secondary Continental Europe Cuvier used fossils to prove the existence of Quaternary gravels Sicilian strata several unique ages in Unusual mammals Tertiary the history of the Earth London clay Parisian gypsum beds prior toCretaceous the appearance Parisian chalk English chalk of humankind. Oolites alluvium Modern mammals Extinct fish andJura reptiles Mt. strata Jurassic New Red Sandstone Triassic Lias Muschelkalk - Trias “Fossils alone reveal Permian successive epochs in Coal Measures Carboniferous Mountain Limestone Shelly fossils,the butformation of the Old Red Sandstone Devonshire strata Devonian no vertebratesglobe.” Magnesian Limestone Perm strata Transitional Wenlock Limestone Silurian Welsh Greywackes Ordovician Cambrian Primary No fossils Crystalline (metamorphic) strata Precambrian William Smith (1769-1839) surveyor, civil engineer Smith’s work as a surveyor and canal digger allowed him to create the first accurate geologic map of a large region. Time His careful observations of fossils allowed Smith to identify strata that were equivalent in age no matter where he found them in Great Britain. Smith discovered that fossil species occur in a unique, non-repeating sequence through time. Other geologists picked up on this observation and began using the fossil record to correlate rock formations. Why species changed through time was still an open question. By the early 1800’s geologists had established… • • • • A long history for the Earth The existence of a fossil record of past, extinct, species Methods for interpreting past events from rock layers A way to date rocks and correlate them from place to place by comparing their fossils. • Missing was an explanation for the origin and extinction of life on Earth through time. Hutton Cuvier Lyell Smith Charles Darwin (1809-1882) • Son of a wealthy doctor. Went to medical school but dropped out. • Took geology with Professor Jameson, a neptunist. He did not enjoy his lectures. “The sole effect they produced on me was the determination never as long as I lived to read a book on Geology or in any way to study the science.” • Enrolled at Cambridge to study Divinity. • Enjoyed classics and theology, but spent most of his time hanging out with zoologists, botanists, and geologists, developing a keen interest in natural history. Charles Darwin • Darwin began cultivating an active interest in geology at Cambridge. • He joined his geology professor, the Reverend Adam Sedgwick, on a two-week expedition mapping the rock strata of Wales (part of Sedgwick’s Cambrian project. Grab your hammer and clinometer Charles - there’s work to be done! Darwin graduated and would have entered the Anglican priesthood, but for an unusual job offer…. The Voyage of the Beagle • Darwin is offered the role of “captain’s companion” on a survey voyage of the HMS Beagle. • Captain Fitzroy is looking for a gentleman naturalist to join the crew on a survey of the coast of South America. • 1831 - Darwin sets sail on a two year expedition aboard the Beagle. •The Beagle spends 5 years circumnavigating South America and the Southern Hemisphere. •Darwin spends most of that time onshore - traveling, exploring, collecting, and keeping detailed notebooks and a journal. Voyage of the Beagle The Voyage of the Beagle •Darwin observes and collects animals, plants, and fossils. •He studies the geology of South America and of the islands he visits. •Carries with him Principles of Geology by Sir Charles Lyell. Geologists in the 1800s were very concerned with questions of origin: the origin of different rock types, the origin of different sedimentary formations, geologic features, etc. Based on his observations on the Beagle voyage, Darwin worked out the origin of coral atolls from volcanic islands. Fossils Darwin found in S. America led him to question the origin of species. Glyptodon ? Megatherium ? This wonderful relationship in the same continent between the dead and the living, will, I do not doubt, hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts. Darwin observed two similar species of ‘ostrich’ separated by the Rio Negro in Argentina. American Rhea Darwin’s Rhea He puzzled over why there should be two similar species of this bird occupying the same habitat in 20 adjacent regions. Darwin experienced a powerful earthquake while ashore in Chile. Exploring the coastline he saw areas where the sea floor had been uplifted several meters above sea level. Later, Darwin noted fossil seashells in the rock strata high up in the Chilean Andes. He surmised that the rocks in the high peaks had been uplifted from sea level over a very long time in a manner analogous to the uplift he saw from the earthquake. The power of small changes, added together over geological spans of time, would become an important theme in Darwin’s thinking. One last stop in S. America: The Galápagos Islands Pinta Marchena Genovesa (Tower) 0° Santiago Santa Cruz Fernandina Santa Fé San Cristóbal Isabela Floreana Espánola The Galapagos Islands are named for the giant tortoises that live there. Darwin was impressed by the large number of species unique to these islands, including the tortoises. Marine iguanas - unique to the Galapagos Islands Galapagos land iguana - lives on the same islands as the marine iguana, but feeds on cactus instead of seaweed. The Galapagos penguin the only penguin that lives near the equator! The flightless cormorant almost identical to its mainland cousins except for the stubby, useless wings! Opuntia cactus - we have them growing on the Hofstra campus, but not as trees! After returning home, Darwin realized that some Galápagos animals and plants were found showing uncommon variety, often with each island populated by unique species. “Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.” Darwin was puzzled by what he saw on the Galápagos Islands • Absence of native mammals and frogs in the Galápagos. • Galápagos animals and plants were clearly similar to those he had seen on the South American mainland, but they were different species. • Why should these small, similar islands, mostly within sight of each other, have so many unique species of plants and animals, many peculiar to a particular island? “…it is the circumstance, that several of the islands possess their own species of the tortoise, mocking thrush, finches, and numerous plants, …that strikes me with wonder.” Darwin was also impressed with the volcanic landscapes of the Galápagos and realized that the islands were geologically very new. “Seeing every height crowned with its crater, and the boundaries of most of the lava-streams still distinct, we are led to believe that within a period, geologically recent, the unbroken ocean was here spread out.” “[In the Galapagos], both in space and time, we seem to be brought somewhat near to that great fact–that mystery of mysteries–the appearance of new beings on this earth.” After returning to England, Darwin began a series of investigations into the question of organic evolution that would occupy him for the rest of his life. “ From this work I became convinced that species are not immutable. It is like confessing a murder.” By the end of 1838, Darwin had a working hypothesis for explaining how species could change over time in a way that left them adapted to their circumstances. “This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.” Individuals vary in their traits This process repeats itself with each generation Reproduction makes an excess of offspring (Malthus) Evolution through Natural Selection Offspring with traits well-suited to the environment survive and reproduce. Offspring with unfavorable traits fail to survive or reproduce On the Origin of Species • 1859 Darwin publishes On the Origin of Species by Means of Natural Selection. • The book is a sensation - by 1876 it has sold over 16,000 copies in England and has been translated into every major language. “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” On the Origin of Species (1859) • Marshaled a large body of evidence in support of the fact of evolution (that all species living and extinct are descended from other species). • Developed a materialistic (nonsupernatural) explanation for the formation of new species and for the appearance of design in adaptation. • Mechanism of natural selection is plausible and testable. • In later books, Darwin argued that Humankind could not be excluded from his theory.