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GE 121 Physical and Historical Geology I GE 122 Physical and Historical Geology II Expanded course objectives Earth’s Dynamic Systems 10th Edition Hamblin, W.K. and Christiansen, E.H. Planet Earth Major Concepts 1. A comparison of Earth with other inner planets provides insight into the distinguishing characteristics of our planet and what makes it unique. 2. Earth's atmosphere is a thin shell of gas surrounding the planet. It is a fluid, in constant motion. Other planets have atmospheres, but Earth's is unique because it is 78% nitrogen and 21% oxygen. 3. The hydrosphere is another feature that makes Earth unique. Water moves in a great, endless cycle from the ocean to the atmosphere, over the land surface, and back to the sea again. 4. The biosphere exists because of water. Although it is small compared to other layers of Earth, it is a major geologic force operating at the surface. 5. Continents and ocean basins are the largest-scale surface features of Earth. 6. The continents consist of three major components: (a) ancient shields, (b) stable platforms, and (c) belts of folded mountains. Each reveals the mobility of Earth's crust. 7. The ocean floor contains several major structural and topographic divisions: (a) the oceanic ridge, (b) the vast abyssal floor, (c) trenches, (d) seamounts, and (e) continental margins. 8. Earth is a differentiated planet, with its materials segregated into layers according to density. The internal layers based on composition are (a) crust, (b) mantle, and (c) core. The major internal layers based on physical properties are (a) lithosphere, (b) asthenosphere, (c) mesosphere, (d) outer core, and (e) inner core. Material within each of these units is in motion, making Earth a changing, dynamic planet. Geologic Systems Major Concepts 1. A natural system is a group of interdependent components that interact to form a unified whole and are under the influence of related forces. The materials in a system change in an effort to reach and maintain equilibrium. 2. Earth's system of moving water, the hydrologic system, involves the movement of water—in rivers, as groundwater, in glaciers, in oceans, and as water vapor in the atmosphere. As water moves, it erodes, transports, and deposits sediment, creating distinctive landforms and rock bodies. 3. Radiation from the Sun is the source of energy for Earth's hydrologic system. 4. A system of moving lithospheric plates—the plate tectonic system—explains Earth's major structural features. It operates from Earth's internal heat. 5. Where plates move apart, hot material from the mantle wells up to fill the void and creates new lithosphere. The major features formed where plates spread apart are continental rifts, oceanic ridges, and new ocean basins. 6. Where plates converge, one slides beneath the other and plunges down into the mantle. The major features formed at convergent plate margins are folded mountain belts, volcanic arcs, and deep-sea trenches. 7. Where plates slip horizontally past one another, transform plate boundaries develop on long, straight faults. Shallow earthquakes are common. 8. Far from plate margins, plumes of less-dense mantle material rise to shallow levels, feeding within-plate volcanoes and producing minor flexures of the lithosphere. 9. Earth's crust floats on the denser mantle beneath. The crust rises and sinks in attempts to maintain isostatic equilibrium. Minerals Major Concepts 1. An atom is the smallest unit of an element that possesses the properties of the element. It consists of a nucleus of protons and neutrons and a surrounding cloud of electrons. 2. An atom of a given element is distinguished by the number of protons in its nucleus. Isotopes are varieties of an element, distinguished by the different numbers of neutrons in their nuclei. 3. Ions are electrically charged atoms, produced by a gain or loss of electrons. 4. Matter exists in three states: (a) solid, (b) liquid, and (c) gas. The differences among the three are related to the degree of ordering of the atoms. 5. A mineral is a natural solid possessing a specific internal atomic structure and a chemical composition that varies only within certain limits. Each type of mineral is stable only under specific conditions of temperature and pressure. 6. Minerals grow when atoms are added to the crystal structure as matter changes from the gaseous or the liquid state to the solid state. Minerals dissolve or melt when atoms are removed from the crystal structure. 7. All specimens of a mineral have well-defined physical and chemical properties (such as crystal structure, cleavage or fracture, hardness, and density). 8. Silicate minerals are the most important minerals and form more than 95% of Earth's crust. The most important silicates are feldspars, micas, olivines, pyroxenes, amphiboles, quartz, and clay minerals. Important non-silicate minerals are calcite, dolomite, gypsum, and halite. 9. Minerals grow and are broken down under specific conditions of temperature, pressure, and chemical composition. Consequently, minerals are a record of the changes that have occurred in Earth throughout its history. Igneous Rocks Major Concepts 1. Magma is molten rock that originates from the partial melting of the lower crust and the upper mantle, usually at depths between 10 and 200 km below the surface. 2. The texture of a rock provides important insight into the cooling history of the magma. The major textures of igneous rocks are (a) glassy, (b) aphanitic, (c) phaneritic, (d) porphyritic, and (e) pyroclastic. 3. Most magmas are part of a continuum that ranges from mafic magma to silicic magma. 4. Silicic magmas produce rocks of the granite-rhyolite family, which are composed of quartz, K-feldspar, Na-plagioclase, and minor amounts of biotite or amphibole. 5. Basaltic magmas produce rocks of the gabbro-basalt family, which are composed of Caplagioclase and pyroxene with lesser amounts of olivine and little or no quartz. 6. Magmas with composition intermediate between mafic and silicic compositions produce rocks of the diorite-andesite family. 7. Basalt, the most abundant type of extrusive rock, typically erupts from fissures to produce relatively thin lava flows that cover broad areas or from central vents to produce shield volcanoes and cinder cones. Volcanic features developed by intermediate to silicic magmas include viscous lava flows, ash-flow tuff, composite volcanoes, and collapse calderas. The abundance of water in silicic magma is critical to its development and eruption. 8. Masses of igneous rock formed by the cooling of magma beneath the surface are called intrusions or plutons. The most important types of intrusions are batholiths, stocks, dikes, sills, and laccoliths. 9. The wide variety of magma compositions is caused by variations in: (1) the composition of the source rocks, (2) partial melting, (3) fractional crystallization, (4) mixing, and (5) assimilation of solid rock into the molten magma. 10. Most basaltic magma is generated by partial melting of the mantle at divergent plate boundaries and in rising mantle plumes. Most intermediate to silicic magma is produced at convergent plate boundaries. Partial melting of continental crust at rifts and above plumes can also produce silicic magma. Sedimentary Rocks Major Concepts 1. Sedimentary rocks are formed at Earth's surface by the hydrologic system. Their origin involves the weathering of preexisting rock, transportation of the material away from the original site, deposition of the eroded material in the sea or in some other sedimentary environment, followed by compaction and cementation. 2. Two main types of sedimentary rocks are recognized: (a) clastic rocks and (b) chemically precipitated rocks and organic rocks. 3. Stratification is the most significant sedimentary structure. Other important structures include cross-bedding, graded bedding, ripple marks, and mud cracks. 4. The major sedimentary systems are (a) fluvial, (b) alluvial-fan, (c) eolian, (d) glacial, (e) delta, (f) shoreline, (g) organic-reef, (h) shallow-marine,(i) submarine fan, and (j) deepmarine systems. 5. Sedimentary rock layers can be grouped into formations and formations can be grouped into sequences that are bound by erosion surfaces. These formations and sequences form an important interpretive element in the rock record. 6. Plate tectonics has had a profound effect on the genesis of sedimentary rocks by controlling the geologic setting in which various types of sediment sequences are formed and the climate zones into which continents drift. Metamorphic Rocks Major Concepts 1. Metamorphic rocks can be formed from igneous, sedimentary, or previously metamorphosed rocks by recrystallization in the solid state. The driving forces for metamorphism are changes in temperature, pressure, and composition of their pore fluids. 2. These changes produce new minerals, new textures, and new structures within the rock body. Careful study of metamorphic rocks reveals the thermal and deformation history of Earth's crust. 3. The textures of metamorphic rocks are unique and tell their stories of solid-state recrystallization and deformation. During metamorphism, new platy mineral grains grow in the direction of least stress, producing a planar rock structure called foliation. Rocks with only one mineral (such as limestone) or those that recrystallize in the absence of deforming stresses do not develop strong foliation but instead develop a granular texture. Mylonitic rocks develop where shearing along a fracture forms small grains by ductile destruction of larger grains. 4. The major types of foliated metamorphic rocks include slate, schist, gneiss, and mylonite; important nonfoliated rocks include quartzite, marble, hornfels, greenstone, and granulite. They are distinguished by their textures and secondarily by their compositions. 5. Contact metamorphism is a local phenomenon associated with thermal and chemical changes near the contacts of igneous intrusions. Regional metamorphism is best developed in the roots of mountain belts along convergent plate boundaries. 6. Mineral zones are produced where temperature, pressure, or fluid compositions varied systematically across metamorphic belts or around igneous intrusions. 7. Distinctive sequences of metamorphic rocks are produced in each of the major plate tectonic settings. Structure of Rock Bodies Major Concepts 1. Deformation of Earth's crust is well documented by historical movement along faults, by raised beach terraces, and by deformed rock bodies. 2. Folds in rock strata range in size from microscopic wrinkles to large structures hundreds of kilometers long. The major types of folds are (a) domes and basins, (b) plunging anticlines and synclines, and (c) complex folds. 3. Faults are fractures, along which slippage or displacement has occurred. The three basic types are (a) normal faults, (b) thrust faults, and (c) strike-slip faults. 4. Joints are fractures in rocks along which there is no horizontal or vertical displacement. 5. Rocks deform when applied stress exceeds their strength. They may deform by ductile flow or brittle fracture. Geologic Time Major Concepts 1. The interpretation of past events in Earth's history is based on the principle that the laws of nature do not change with time. 2. Relative dating (determining the chronological order of a sequence of events) is achieved by applying the principles of (a) superposition, (b) faunal succession, (c) crosscutting relations, (d) inclusions, and (e) succession in landscape development. 3. The standard geologic column was established from studies of rock sequences in Europe. It is now used worldwide. Rocks were originally correlated from different parts of the world largely based on the fossils they contain. Today, radiometric dating can be used to correlate major rock sequences. 4. Numerical time designates a specific duration of time in units of hours, days, or years. In geology, long periods of absolute time can be measured by radiometric dating. Weathering Major Concepts 1. Weathering is the breakdown and alteration of rocks at Earth's surface through physical and chemical reactions with the atmosphere and the hydrosphere. 2. Physical weathering is the mechanical fragmentation of rocks from stress acting on them. Ice wedging may be the most important type. 3. Chemical weathering involves chemical reactions with minerals that progressively decompose the solid rock. The major types of chemical weathering are dissolution, acid hyrdolysis, and oxidation. 4. Joints and fractures facilitate weathering because they permit water and gases in the atmosphere to attack a rock body at considerable depth. They also greatly increase the surface area on which chemical reactions can occur. 5. The major products of weathering are spheroidal rock forms, a blanket of regolith, and dissolved ions. Soil is the upper part of the regolith—a mixture of clay minerals, weathered rock particles, and organic matter. 6. Climate greatly influences the type and rate of weathering. Slope Systems Major Concepts 1. Mass movement is the downslope transfer of material through the direct action of gravity. It is a major geologic process operating on all slopes. 2. The most important factors influencing slope failures are saturation of slope material with water, earthquakes, over steepening of slopes, and freezing and thawing. 3. The major types of mass movement are creep, debris flows, landslides, and subsidence. 4. Creep is the very slow downslope movement of soil and rock, produced primarily by the expansion and contraction of the surface materials. 5. Debris flows are mixtures of rock fragments and water that flow downslope as a viscous fluid. A lahar is a special type of debris flow composed of volcanic materials. 6. Landslides are a type of mass movement in which the material moves as a unit or block along definite slippage planes. 7. Subsidence differs from other types of mass movement in that it has essentially vertical motion caused by collapse into voids or as a result of compaction of loose materials. 8. Slopes are open dynamic systems in which regolith and near-surface bedrock move downslope toward the main stream, where they are removed through the drainage system. River Systems Major Concepts 1. Running water is part of Earth's hydrologic system and is the most important agent of erosion. Stream valleys are the most abundant and widespread landforms on the continents. 2. A river system consists of a main channel and all of the tributaries that flow into it. It can be divided into three subsystems: (1) a collecting system, (2) a transporting system, and (3) a dispersing system. 3. The most important variables in stream flow are (1) discharge, (2) velocity, (3) gradient, (4) sediment load, and (5) base level. 4. The variables in a stream constantly adjust toward a state of equilibrium. 5. Rivers erode by (1) removing regolith, (2) downcutting, and (3) headward erosion. 6. As a river develops a low gradient, it deposits part of its load on point bars, on natural levees, and across the surface of its floodplain. 7. Most of a river's sediment is deposited where the river empties into a lake or ocean. This deposition commonly builds a delta at the river's mouth. In arid regions, many streams deposit their loads as alluvial fans at the base of steep slopes. 8. The origin and evolution of the world's major rivers are controlled by the tectonic and hydrologic systems. Groundwater Systems Major Concepts 1. Groundwater is an integral part of the hydrologic system, and it is intimately related to surface water drainage. 2. The movement of groundwater is controlled largely by the porosity and permeability of the rocks through which it flows. 3. The water table is the upper surface of the zone of saturation. 4. Groundwater moves slowly through the pore spaces in rocks by the pull of gravity. 5. The natural discharge of groundwater is generally into springs, streams, marshes, and lakes. 6. Artesian water is confined under pressure, like water in a pipe. It occurs in permeable beds bounded by impermeable formations. 7. Erosion by groundwater produces karst topography, which is characterized by caves, sinkholes, solution valleys, and disappearing streams. Precipitation of minerals from groundwater creates deposits in caves and along fractures and cements many kinds of clastic sedimentary rocks. 8. Alteration of the groundwater system can produce many unforeseen problems, such as pollution, subsidence, sinkhole collapse, and disruption of ecosystems. Glacial Systems Major Concepts 1. Glaciers are systems of flowing ice that form where more snow accumulates each year than melts. 2. As ice flows, it erodes the surface of the land by abrasion and plucking. Sediment is transported by the glacier and deposited where the ice melts. In the process, the landscape is greatly modified. 3. The two major types of glaciers—continental and valley glaciers—produce distinctive erosional and depositional landforms. 4. The Pleistocene ice age began 2 to 3 million years ago and terminated, in most areas, about 5,000 years ago. During the ice age, there were a number of glacial and interglacial epochs. 5. The major effects of an ice age include glacial erosion and deposition, modification of drainage systems, creation of numerous lakes, the fall of sea level, isostatic adjustments of the lithosphere, and migration and selective extinction of plant and animal species. 6. Periods of glaciation have been rare events in Earth's history. The causes of glacial episodes are not completely understood, but they may be related to several simultaneously occurring factors, such as astronomical cycles, plate tectonics, and ocean currents. Shoreline Systems Major Concepts 1. Wind-generated waves provide most of the energy for shoreline processes. 2. Wave refraction concentrates energy on headlands and disperses it in bays. 3. Longshore drift, generated by waves advancing obliquely toward the shore, transports sediment parallel to the coast. It is one of the most important shoreline processes. 4. Erosion along a coast tends to develop sea cliffs by the undercutting action of waves and longshore currents. As a cliff recedes, a wave-cut platform develops, until equilibrium is established between wave energy and the shape of the coast. 5. Sediment transported by waves and longshore current is deposited in areas of low energy to form beaches, spits, and barrier islands. 6. Erosion and deposition along a coast tend to develop a straight or gently curving shoreline that is in equilibrium with the energy expended upon it. 7. Reefs grow in tropical climates and thrive only in shallow, clear marine waters. Fringing reefs around volcanic islands can evolve into atolls. 8. The worldwide rise in sea level, associated with the melting of the Pleistocene glaciers, drowned many coasts between 15,000 and 20,000 years ago. Coasts are classified based on the process—subaerial or marine—that has been most significant in developing their configurations or upon their tectonic setting. 9. Tides are produced by the gravitational attraction of the Moon and locally exert a major influence on shorelines. 10. Tsunamis are waves generated by earthquakes, volcanic eruptions, and submarine landslides that disturb the sea floor. Eolian Systems Major Concepts 1. Wind is not an effective agent in eroding the landscape, but it can produce deflation basins and yardangs as well as small pits and grooves on rocks. 2. The major result of wind activity is the transportation of loose, unconsolidated fragments of sand and dust. Wind transports sand by saltation and surface creep. Dust is transported in suspension, and it can remain high in the atmosphere for long periods. 3. Sand dunes migrate as sand grains are blown up and over the windward side of the dune and accumulate on the lee slope. The internal structure of a dune consists of strata inclined in a downwind direction. 4. Various types of dunes form, depending on wind velocity, sand supply, constancy of wind direction, and characteristics of the surface over which the sand migrates. 5. Windblown dust (loess) forms blanket deposits, which can mask the older landscape beneath them. The source of loess is desert dust or the fine rock debris deposited by glaciers. 6. Desertification, the loss of farmable land on the margins of deserts, can be caused by human activity or by slight climatic fluctuations Plate Tectonics Major Concepts 1. The theory of continental drift was proposed in the early 1900s and was supported by a variety of geologic evidence. Without knowledge of the nature of the oceanic crust, however, a complete theory of Earth's dynamics could not have been developed. 2. A major breakthrough in the development of the plate tectonics theory occurred in the early 1960s when the topography of the ocean floors was mapped and magnetic and seismic characteristics of the oceanic crust were determined. 3. Most tectonic activity occurs along plate boundaries. Divergent plate boundaries are zones where the plates split and spread apart. Convergent plate boundaries are zones where plates collide. Transform fault boundaries are zones where plates slide horizontally past each other. 4. The direction of the relative motion of plates is indicated by (a) the trend of the oceanic ridge and associated transform faults, (b) seismic data, (c) magnetic stripes on the seafloor, and (d) the ages of chains of volcanic islands and seamounts. The motion of a plate can be described in terms of rotation around a pole. 5. Heat flow from the core and the mantle (generated by radioactivity) is probably the fundamental cause of Earth's internal convection. 6. The major forces acting on plates are (a) slab-pull, (b) ridge-push, (c) basal drag, and (d) friction along transform faults and in subduction zones. The most important forces that make the plates move are probably slab-pull and ridge push. Seismicity and Earth's Interior Major Concepts 1. Seismic waves are vibrations in Earth caused by the rupture and sudden movement of rock. 2. Three types of seismic waves are produced by an earthquake shock: (a) P waves, (b) S waves, and (c) surface waves. 3. The primary effect of an earthquake is ground motion. Secondary effects include (a) landslides, (b) tsunamis, and (c) regional or local uplift or subsidence. 4. The exact location and timing of an earthquake cannot be predicted. However, seismic risk can be evaluated and, in areas with high risk, preparations for future earthquakes can be made. 5. Most earthquakes occur along plate boundaries. Divergent plate boundaries and transform fault boundaries produce shallow-focus earthquakes. Convergent plate boundaries produce an inclined zone of shallow-focus, intermediate-focus, and deepfocus earthquakes. 6. The velocities at which P waves and S waves travel through Earth indicate that Earth has a layered internal structure based on composition—crust, mantle, and core. It also has a solid inner core, a liquid outer core, a weak asthenosphere, and a rigid lithosphere. 7. Plate tectonics and upwelling and downwelling plumes are the most important manifestations of Earth's internal convection. The magnetic field is probably caused by convection of the molten iron core. Divergent Plate Boundaries Major Concepts 1. Divergent plate boundaries are zones where lithospheric plates move apart from one another. They are characterized by tensional stresses that typically produce long rift zones, normal faults, and basaltic volcanism. 2. An oceanic ridge marks divergent plate boundaries in the ocean basins. It is a broad fractured swell with a total length of about 70,000 km. Basaltic volcanism and earthquakes are concentrated along the rift zone at the ridge crest. 3. The ridge is broken into segments and its characteristics depend upon the rate of spreading. 4. Oceanic crust is generated at divergent plate boundaries and is composed of four major layers: (a) deep marine sediment, (b) pillow basalts, (c) sheeted dikes, and (d) gabbro. Below the crust lies a zone of sheared peridotite in the upper mantle. 5. At divergent plate boundaries, basaltic magmatism results from decompression melting of the mantle. The magma then collects into elongate chambers beneath the ridge and some is intruded as dikes or extruded along the rift zone. 6. As the oceanic lithosphere moves away from the ridge it cools, becomes thicker and more dense, and subsides. 7. Seawater is heated as it circulates through the hot crust and causes extensive hydrothermal alteration and large volumes of metamorphosed basalt. Locally, the hydrothermal fluid vents to produce hot springs on the seafloor. 8. Continental rifting occurs where divergent plate margins develop in continents. The East African rift, the Red Sea, and the Atlantic Ocean show various steps in a progression from continental rifting to seafloor formation. 9. Continental rifting creates new continental margins marked by normal faults and volcanic rocks interlayered with thick sequences of continental sedimentary rocks. As the continental margin subsides, it is gradually buried by a thick layer of shallow marine sediments. Transform Plate Boundaries Major Concepts 1. Transform plate boundaries are unique, in that the plates move horizontally past each other on strike-slip faults. Lithosphere is neither created nor destroyed. 2. The three major types of transform boundaries are: (1) a ridge-ridge transform, which connects two segments of a divergent plate boundary; (2) a ridge-trench transform, which connects a ridge and a trench; and (3) a trench-trench transform, which connects two convergent plate boundaries. 3. Transform plate boundaries are shearing zones where plates move past each other without diverging or converging. In the shearing process, secondary features are created, including parallel ridges and valleys, pull-apart basins, and belts of folds. Compression and extension develop only in small areas. 4. Oceanic fracture zones are prominent linear features that trend perpendicular to the oceanic ridge. They may be several kilometers wide and thousands of kilometers long. The structure and topography of oceanic fracture zones depend largely on two things: the temperature (or age) difference across the fracture, and the spreading rate of the oceanic ridge. 5. Continental transform fault zones are similar to oceanic transforms, but they lack fracture zone extensions. 6. Shallow earthquakes are common along transform plate boundaries; they are especially destructive on the continents. 7. Volcanism is rare along transform plate boundaries, but small amounts of basalt erupt locally from leaky transform faults. 8. Metamorphism in transform fault zones creates rocks with strongly sheared fabrics, as well as hydrated crustal and even mantle rocks. Convergent Plate Boundaries Major Concepts 1. Convergent plate boundaries are zones where lithospheric plates collide. The three major types of convergent plate interactions are (a) convergence of two oceanic plates, (b) convergence of an oceanic and a continental plate, and (c) collision of two continental plates. The first two involve subduction of oceanic lithosphere into the mantle. 2. Plate temperatures, convergence rates, and convergence directions play important roles in determining the final character of a convergent plate boundary. 3. Most subduction zones are marked by an outer swell, a trench and forearc, a magmatic arc, and a backarc basin. In contrast, continental collision produces a wide belt of folded and faulted mountains in the middle of a new continent. 4. Subduction of oceanic lithosphere produces a narrow, inclined zone of earthquakes that extends to more than 600 km depth, but broad belts of shallow earthquakes form where two continents collide. 5. Crustal deformation at subduction zones produces melange in the forearc, and extension or compression in the volcanic arc and backarc areas. Continental collision is always marked by strong horizontal compression that causes folding and thrust-faulting. 6. Magma is generated at subduction zones because dehydration of oceanic crust causes partial melting of the overlying mantle. Andesite, and other silicic magmas that commonly erupt explosively, are distinctive products of convergent plate boundaries. At depth, plutons form, composed of rock ranging from diorite to granite. In continental collision zones, magma is less voluminous, dominantly granitic, and probably derived by melting of preexisting continental crust. 7. Metamorphism at subduction zones produces low-temperature/high-pressure facies near the trench and higher-temperature facies near the magmatic arc. Broad belts of highly deformed regional metamorphic rocks mark the sites of past continental collision. 8. Continents grow larger as low-density silica-rich rock is added to the crust at convergent plate boundaries. Hotspots and Mantle Plumes Major Concepts 1. Mantle plumes appear to be long, nearly vertical columns of hot, upwelling solids that ascend from the core-mantle boundary. They rise upward because they are lower in density and therefore buoyant. At the surface, they create hotspots with high heat flow, volcanic activity, and broad crustal swells. 2. A plume evolves in two stages. When a plume starts, it develops a large, bulbous head that rises through the mantle. As the head deforms against the strong lithosphere, crustal uplift and voluminous volcanism occur. The second stage is marked by the effects of a still rising but narrow tail. 3. Basaltic magma is created because of decompression of the rising hot plume. Magmas formed in mantle plumes are distinctive and show hints of being partially derived from ancient subducted slabs that descended deep into the mantle. 4. A starting plume that rises beneath the ocean floor produces a large plateau of flood basalt on the seafloor. Subsequently, a narrow chain of volcanic islands forms above the tail of the plume, revealing the direction of plate motion. 5. If a plume develops beneath a continent, it may cause regional uplift and eruption of continental flood basalts. Rhyolitic caldera systems develop when continental crust is partially melted by hot basaltic magma from the plume. Continental rifting and the development of an ocean basin may follow. 6. Plumes may affect the climate system and Earth's magnetic field. Other Planets Major Concepts 1. Impact cratering was the dominant geologic process in the early history of all planetary bodies in the solar system. 2. Earth, the Moon, Mercury, Venus, and Mars form a family of related planets, known as the inner planets, that probably experienced similar sequences of events in their early histories. 3. Both the Moon and Mercury are primitive bodies, and their surfaces have not been modified by hydrologic and tectonic systems. Much of their surfaces are ancient and heavily cratered. 4. Mars has had an eventful geologic history involving crustal uplift, volcanism, stream erosion, and eolian activity. Huge tracts of cratered terrain remain but are intensely eroded. Liquid water may have existed on its surface, and there is controversial new evidence that life may have evolved there. 5. The surface of Venus is dominated by relatively young volcanic landscapes and such tectonic features as faults and folded mountain belts. The crust of Venus does not appear to be broken into tectonic plates, however, and much of its evolution is related to the development of mantle plumes. 6. Cratering on the icy moons of Jupiter, Saturn, Uranus, and Neptune suggests that a period of intense bombardment affected the entire solar system more than 4 billion years ago. 7. Most of the icy moons of Uranus and Neptune show evidence of geologic activities such as volcanic extrusions of slushy ice and rifting. 8. Asteroids and comets are the smallest members of the solar system. They appear to be remnants of the bodies that accreted to form the larger planets. 9. The planets formed in a thermal gradient around the Sun. The inner planets are thus rich in silicates and iron, which are stable at high temperature, and the outer planetary bodies have large amounts of ice, which is stable at low temperature. 10. The geologic evolution of a planet depends on its source of heat energy, its size, and its composition. Evolution of the Earth Donald R. Prothero / Robert H. Dott, Jr. Tabel Of Contents Chapter 1 Time and Terrestrial Change 3 Dramatic Geologic Events in Human History 4 Subtle Geologic Events in Human History 6 Climate 6 Glaciers and Sea Level 7 Crustal Changes 8 Box 1.1 Human Beings as Geologic Agents 9 How Fast Is Fast? Time and Rates of Geologic Processes 9 Examples of Rates 10 Different Ways of Growing and Changing 11 Catastrophic Versus Uniform Views of Change and the Age of the Earth 12 Summary 13 Readings 13 Chapter 2 Floods, Fossils, and Heresies 15 What Is a Fossil? 16 Early Questions 16 Da Vinci’s Insight 17 Steno’s Principles 17 Utility of Fossils 18 Fossils and Geologic Mapping 18 Box 2.1 Robert Hooke and the Meaning of Fossils 18 Principle of Fossil Correlation and Index Fossils 22 Explanations of Change Among Fossils 22 Catastrophism 22 Descent by Evolution 23 Box 2.2 Mark Twain Winks at Paleontology 24 First Unified Hypotheses of the Earth 24 The Cosmogonists 24 Buffon’s Break with Genesis 24 The First True Geologic Chronology 24 Neptunism 25 A. G. Werner 25 Heated Basalt Controversy 26 Plutonism—the Beginning of Modern Geology 26 James Hutton 26 An Old Dynamic Earth 26 “Nothing in the Strict Sense Primitive” 27 Basalt 27 Granite and Mineral Veins 27 Evidence of Upheaval of Mountains 27 Charles Lyell’s Uniformity of Nature 29 Evolution—Lyell’s Ultimate Challenge 30 Box 2.3 Uniformitarianism in the Public Eye 30 Equilibrium and Feedback 31 The Doctrine of Uniformity Today 31 Scientific Methodology of Geology 32 Historical Science 32 Geologic Reasoning 32 Box 2.4 Gradualism Meets the Scablands 33 Summary 35 Readings 36 Chapter 3 Evolution 39 The Evolution of Evolution 40 Buffon’s Evolution 40 Erasmus Darwin: Did He Begin It All? 41 Lamarckian Evolution 41 Inheritance of Acquired Characteristics 42 Charles Darwin and Natural Selection 43 Evidence of Evolution 45 Reality of Evolution 50 Genetics and the Evolutionary Synthesis 50 Box 3.1 Mendelian Genetics and Molecular Biology 51 The Origin of Species 53 The Fossil Record and Evolution 55 Challenges to the Neo-Darwinian Synthesis 58 Neutralism 58 Inheritance of Acquired Characteristics Revisited 59 Macroevolution 59 Evolution and Creationism 62 Summary 63 Readings 65 Chapter 4 The Relative Geologic Time Scale and Modern Concepts of Stratigraphy 67 Early Mapping and Correlation of Strata 68 Modern Relative Time Scale 69 Box 4.1 Nothing Quite Like a Good Fight . . . 71 Rocks Versus Time 71 Box 4.2 Corollaries to Superposition for Determining Relative Age 72 The Formation 73 Lateral Variations 73 Depositional Environments and Sedimentary Facies 74 Definition of Sedimentary Facies 74 Regional Analysis of Facies 75 Transgression and Regression by the Sea 75 Local Versus Worldwide Transgression and Regression 78 Biostratigraphic Concepts 78 Unconformities 80 Some Refinements 80 Unconformity-Bounded Sequences 81 Additional Relative Time Scales 81 A Sense of Time and Rates 83 Summary 83 Readings 84 Chapter 5 The Numerical Dating of the Earth 87 Early Attempts to Date the Earth 88 Kelvin’s Dating of the Earth 88 Box 5.1 Absolute Measures of Time 89 Radioactivity 90 First Dating of Minerals 91 Concept of Decay 91 Box 5.2 Mathematics of Radioactive Decay 92 Modern Isotopic Dating 92 Decay Series Used 92 Daughter Lead Ratios 93 Carbon 14—A Special Case 94 Fission-Track Dating 95 Discordant Dates from Resetting 95 Accuracy of Isotopic Dates 96 Isotopic Time Scale 96 Memorable Dates 97 An Assessment 98 Summary 98 Readings 99 Chapter 6 The Origin and Early Evolution of the Earth 101 Distribution of the Elements 102 Probable Origin of the Earth 102 Hot Origins 102 A Cold Beginning 103 Solar Nebula 103 Recent Modifications 104 Planetology of the Inner Solar System 106 Leftovers—Asteroids, Meteorites, and Comets 107 Nature of the Earth’s Interior 107 Early Speculations 107 Analogies from Meteorites 107 Seismological Evidence of Internal Structure 108 Further Evidence from the Magnetic Field 108 Chemical Composition of the Deep Interior 110 Box 6.1 Major Minerals and Rocks of the Earth’s Crust and Upper Mantle 111 Dawn of Earth History 111 Chemical and Thermal Evolution 111 Origin of the Crust 112 Origin and Evolution of the Atmosphere and Seawater 114 The Problem 114 Outgassing Hypothesis 114 Photochemical Dissociation Hypothesis 114 Oxygen from Photosynthesis 115 Origin of Seawater 116 Ocean-Atmosphere Regulatory Systems 116 Global Chemostat 116 Global Thermostat and Climate 117 Summary 118 Readings 119 Chapter 7 Mountain Building and Drifting Continents 121 Orogenic Belts and Mountain Building 122 The Geosynclinal Concept—Made in America 122 Vertical versus Horizontal Tectonics 124 A Cooling and Shrinking Earth 124 Continental Drift as a Cause of Mountain Building 125 Thermal Convection—Panacea for Mountain Building and Drift? 126 Drift in Eclipse 127 Paleomagnetism—Drift’s Renaissance 127 General Nature of the Sea Floor 130 Rates of Continental Erosion and Oceanic Sedimentation 130 Ocean Ridges 130 Sea-Floor Spreading—A Breakthrough 132 Rifts and Hot Mantle Plumes 132 Age Distribution of Oceanic Islands and Seamounts 133 Major Oceanic Escarpments and Transform Faults 134 Confirmation of Sea-Floor Spreading 135 Sea-Floor Magnetic Anomalies 135 Magnetic-Polarity-Reversal Time Scale 136 Spreading History 137 Plate Tectonics 138 What Drives Them? 140 Plate Collisions 140 Subsidence of Plates and the Accumulation of Sediments 142 Causes of Subsidence 143 Plate Tectonics and Sedimentary Basins 143 Summary 147 Readings 148 Chapter 8 Cryptozoic History: An Introduction to the Origin of Continental Crust 151 Box 8.1 How to Define the Base of the Phanerozoic? 152 Development of a Cryptozoic Chronology 153 Sedgwick in Wales 153 Canadian Shield 153 The Great Lakes Region 154 Great Lakes Correlations 157 Correlation Beyond the Great Lakes 157 Evidence of Crustal Development from Igneous and Metamorphic Rocks 159 Importance of Granite 159 Significance of Isotopic Date Patterns 160 Interpretation of Crustal Development from Sediments 162 Bias of the Record 162 Terrigenous Versus Nonterrigenous Sediments 162 Textural Maturity 162 Box 8.2 Geology’s First Important Instrument 163 Compositional Maturity 163 Stratification 163 The Cryptozoic Sedimentary and Volcanic Record 165 Ancient Archean Rocks 165 Early and Middle Proterozoic Sediments 167 Late Proterozoic Rocks 169 The Cryptozoic Ocean and Atmosphere 170 Orthodox View 170 An Alternative View 171 Box 8.3 Possible Highlights in the Chemical Evolution of the Cryptozoic AtmosphereOcean System 172 Cryptozoic Climate 174 Meager Evidence 174 Early Proterozoic Glaciation 174 Late Proterozoic Glaciation 174 Summary 177 Readings 178 Chapter 9 Early Life and Its Patterns 181 The Origin of Life 182 Early Concerns 182 “A Warm Little Pond?” 183 Chicken-or-Egg Problem: RNA or Proteins? 184 Box 9.1 Communities Without Sunlight: Deep-Sea Hydrothermal Vent Faunas 185 Mud, Kitty Litter, and Fool’s Gold 186 The Record of Early Life Before the Paleozoic 187 Metazoans, Vendozoans, and the “Cambrian Explosion” 192 Darwin’s Dilemma 192 Cambrian Explosion of Shelly Invertebrates 193 When the Trilobites Roamed 197 Summary 204 Readings 204 Chapter 10 Earliest Paleozoic History: The Sauk Sequence—An Introduction to Cratons and Epeiric Seas 207 Box 10.1 “SWEATing” It Out 208 Vendian History 209 The Cambrian Craton 210 Structural Modifications of Cratons 210 Development of Arches and Basins 212 Box 10.2 A Primer on Geologic Maps and Diagrams 215 The Sauk Transgression 219 General Setting 219 Mature Quartz Sandstones 220 Change to Carbonate Deposition 222 Importance of Oolite 223 Depth of the Sauk Sea 223 Modern Analogues for the Sauk Epeiric Sea 224 Importance of Episodic Events 226 Early Paleozoic Paleoclimate 227 Summary 228 Readings 229 Chapter 11 The Later Ordovician: Further Studies of Plate Tectonics and the Paleogeography of Orogenic Belts 231 Ordovician Life 232 Explosive Radiation of the “Paleozoic Fauna” 232 Ordovician Extinctions 240 Ordovician History of the North American Craton 240 Mid-Ordovician Regression and the St. Peter Sandstone 240 Later Ordovician (Tippecanoe) Epeiric Sea 241 Shaly Deposits of Later Ordovician Time 241 Box 11.1 Unconformity-Bounded Sequences Revisited 242 Cratonic Basins and Arches 245 Ordovician Mountain Building in the Appalachian Orogenic Belt 245 Evidence of Increasing Structural Mobility 245 Box 11.2 Dividends from Volcanic Ash 246 Evidence for Dating the Mountain Building 246 Paleogeography and Sedimentation Within Orogenic Belts 247 Background 247 Early Ideas About Borderlands 247 Modern Concepts of Borderlands 248 A Modern Analogue 249 Controversy About Sea Level and Sedimentation 250 Plate-Tectonic Interpretation of Taconian Mountain Building 252 Early Paleozoic Passive-Margin Shelf 252 Thrust Loading of the Continental Margin by Collision 253 Relations Across the Atlantic 254 Summary 256 Readings 257 Chapter 12 The Middle Paleozoic: Time of Reefs, Salt, and Forests 259 Middle Paleozoic Life 260 Marine Communities 260 The Age of Fishes 262 Invasion of the Land 264 Late Devonian Mass Extinctions 268 Box 12.1 Fossils as Calendars 270 The Silurian and Early Devonian Continent 271 Aftermath of the Taconian Orogeny 271 A Carbonate-Rich Craton 272 Modern Versus Ancient Carbonate Sedimentation 274 Organic Reefs 275 General Characteristics 275 Silurian and Devonian Organic Reefs 277 Box 12.2 Origin of Dolomite Rocks 278 Marine Evaporite Deposits 279 Restricted-Basin Evaporites 279 Supratidal Sabkha Evaporites 282 Postdepositional Changes 283 The Michigan Basin 283 Paleoclimate and Paleogeography 283 Devonian Strata of the North American Craton 284 Regression and Transgression Again 284 Cratonic Basin Deposition 284 Cratonic Arches 288 The Acadian Orogeny in the Appalachian Belt 289 Evidence of Devonian Orogeny 289 Dating the Orogeny 290 The Catskill Clastic Wedge 291 The Chattanooga Black Shale Enigma 291 The Caledonian Orogenic Belt 291 Structural Symmetry 291 Box 12.3 Origin of Petroleum 292 Catskill-Old Red Sandstone Facies 293 Intracratonic Orogenic Belts 293 Mountain Building in the Arctic and Western Cordillera 294 Physical and Organic Evolution 295 Summary 296 Readings 297 Chapter 13 Late Paleozoic History: A Tectonic Climax and Retreat of the Sea 299 Mississippian Rocks 300 Last Widespread Carbonates 300 Sedimentary and Tectonic Changes 301 Late Paleozoic Repetitive Sedimentation 304 Sedimentary Cycles 304 Coal Swamps 308 Paleogeographic Reconstruction 309 Terminal Paleozoic Emergence of the Continent 310 Permo-Triassic Paleoclimate 310 Box 13.1 The Red Color Problem 313 Tectonics 315 Cratonic Disturbances 315 Appalachian Orogeny 315 Significance of Thrust Faulting 317 Late Paleozoic Mountain Building in Eurasia 320 Gondwanaland 321 The Gondwana Rocks 322 Box 13.2 Paleomagnetic Reconstruction for Drifting Continents 323 Glossopteris Flora 326 Animal Fossils 327 Antarctica—A Triumph of Prediction 327 Paleogeography and Paleoclimate of Pangea 328 Pangean Biogeography 330 Late Paleozoic Life 332 Marine Life 332 Pennsylvanian Coal Swamps and Permian Coniferous Forests 336 Box 13.3 The Advantages of Seeds 339 Swamp Dwellers and Synapsids 340 The Late Permian Catastrophe 344 Summary 347 Readings 348 Chapter 14 The Mesozoic Era: Age of Reptiles and Continental Breakup 351 Extensional Tectonics—Opening of the North Atlantic 352 The Newark Rifts 352 Ocean Basins and Aulacogens 353 The Breakup of Pangea 355 Triassic History of the Craton 355 Jurassic History of the Craton 359 Ancient Navajo Desert 359 Return of the Epeiric Sea 359 The Cordillera 361 Birth of a Mountain Belt 361 Suspect Terranes 363 Sonomia and the Sierran Arc 366 Granitic Rocks of the Sierran Arc 369 Foreland and Forearc Basins 369 The Sevier and Laramide Orogenies 371 Cretaceous Transgression and Sedimentation 376 Worldwide Effects 376 Effects on the Craton 376 Effects in Gulf and Atlantic Coastal Plains 378 Late Mesozoic Paleoclimatology 378 Paleontologic and Sedimentary Evidence 378 Oxygen-Isotope Paleothermometers 379 Cretaceous Climate 379 The Black Shale Problem 379 Life in the Mesozoic 382 The Mesozoic Marine Revolution 382 Marine Vertebrates 387 The Age of Dinosaurs 389 Saurischians and Birds 390 Box 14.1 A Tooth, A Rib, and Some Footprints 394 Box 14.2 Hot or Cold Running Dinosaurs? 398 Ornithischians 399 Flower Power 401 Early Mammals 403 Late Cretaceous Extinctions 404 Fossil Evidence 404 The Impact Hypothesis 406 The Volcanic Hypothesis 407 The Regression Hypothesis 407 An Assessment 408 Summary 410 Readings 411 Chapter 15 Cenozoic History: Threshold of the Present 413 Cenozoic Cordilleran History 414 Phase I: Laramide Orogeny (Latest Cretaceous to Middle Eocene, 70 to 40 m.y. Ago) 414 Phase II: Resumption of Arc Volcanism (Late Eocene–Middle Miocene, 40 to 20 m.y. Ago) 416 Phase III: Complex Teconism (Early Miocene–Present, 20 to 0 m.y. Ago) 422 Tectonic Hypothesis for the Evolution of the Cordillera 429 Pacific Tectonics 432 The Hawaiian Mantle Plume 432 Western and Southern Pacific Tectonics 433 Southeastern Pacific Tectonics 433 Cenozoic Tectonics of Eurasia 434 Early Cenozoic Events 434 The Alpine-Himalayan Belt of Eurasia 434 Effect of India’s Collision with Southeastern Asia 436 When the Tethys Dried Up 437 Cratonic Rifting and Mantle Plumes 437 Coastal Plains and Continental Shelves 440 Passive Successors of and Predecessors to Orogenic Belts 440 Gulf of Mexico Coastal Province 440 The Atlantic Coastal Province and Rejuvenation 441 Cenozoic Climate 443 Life in the Marine Realm 446 The Age of Mammals 449 The Early Cenozoic Adaptive Explosion 449 Paradise Lost 453 Family Trees 453 The Southern Continents 457 Summary 460 Readings 461 Chapter 16 Pleistocene Glaciation and the Advent of Humanity 465 What Is the Pleistocene? 466 Recognition of Continental-Scale Glaciation—A Triumph of Reasoning 466 Diverse Effects of Glaciation 468 General 468 Isostasy 468 Lakes 468 Wind Effects 469 Worldwide Changes in Sea Level 469 Pleistocene Chronology 469 What Caused Glaciations? 479 Climatologic Background 479 Late Cenozoic Climatic Deterioration 479 Types of Glacial Hypotheses 480 Astronomical, or Orbital, Hypotheses 481 Hypotheses of Changing Heat Budget 483 Hypotheses of Paleogeographic Causes 483 The Thermohaline Conveyor Belt and Dansgaard-Oeschger Cycles 484 Where Do We Stand? 485 Pleistocene Climatic Effects upon Life 485 Ranges of Organisms 485 Land Bridges 486 The End of an Era 486 The Evolution of Primates and Humans 489 The Early Hominid Record 492 The Genus Homo 494 Human Entry into America 496 Climate in Human History 496 The Climatic Optimum 496 Medieval Climatic Fluctuations 497 The Little Ice Age 498 The Present and Future 498 Summary 499 Readings 501 Chapter 17 The Best of All Possible Worlds? 503 Three Important Maxims 504 Evolution of the Earth 504 The Idea of Evolution 504 Chemical Evolution of the Earth 505 Evolutionary Feedback 505 Our Place in the Global Ecosystem 506 Effects on Other Life 506 The Impending Ecological Crisis 507 Fouling of the Environment 507 Limits of the Earth’s Resources 512 Nonrenewable Resources 514 Energy—The Ultimate Limit 516 Alternative Futures 521 Summary—What Quality of Life? 522 Readings 524 Appendix I The Classification and Relationships of Living Organisms A-I Appendix II English Equivalents of Metric Measures A-II Glossary G-I Index I-I