Transcript Chapter 1
Chapter 1 Earth System History 1 Earth System History Study of the interconnected physicochemical and biological changes that our planet has experienced over the course of geologic time 2 Guiding Questions • What fundamental principles guide geologists as they reconstruct Earth’s history? • What are the basic kinds of rock and how are they interrelated? • How do geologists unravel the age relations of rocks? • How does the lithosphere relate to Earth’s inner regions, and how does it move and deform? 3 Earth Systems History Earth is an Archive – Geologic record archives Earth’s history – Interaction of complex systems within the planet 4 Foundations of Geology • Principle of Uniformitarianism – There are inviolable laws of nature that have not changed in the course of time – First founding principle of geology • Actualism James Hutton – Application of modern processes to ancient system – Popularized by Charles Lyell Charles Lyell 5 Actualism Modern ripples provide clues to ancient systems. 6 Catastrophism • Earth forms (mountains, Grand Canyon, rock layers, fossils found high in the mountains) were due to catastrophic forces that shaped the world in a relatively short time. • Leads to ‘Young Earth’ concept • Bishop James Ussher of Ireland – October 26, 4004 BC, 9:00 am – ~6000 years 7 Materials and Processes • Rock – Interlocking or bonded grains of matter typically composed of single minerals • Mineral – Naturally occurring inorganic solid element or compound with a particular chemical composition or range of compositions and a characteristic internal structure • Outcrop – Rocky surfaces that stand exposed and are readily accessible for study 8 Rock Cycle • Surface and internal processes link materials to form three rock types: – Igneous – Sedimentary – Metamorphic 9 Igneous Rocks • Formed by cooling of molten material to the point of hardening – Composed of bonded grains, each consisting of a particular mineral • Magma – Molten material that turns into igneous rock 10 Igneous Rocks • Extrusive igneous rocks – harden at the earth’s surface • Intrusive igneous rocks – harden within the earth 11 Sedimentary Rocks • Sediments – Material deposited on Earth’s surface by water, ice, or air – Weathering • Collective term for chemical and physical processes that break down rocks at Earth’s surface – Erosion • Processes that loosen pieces of rock and move them downhill 12 Sedimentary Rocks • Formed from: – Preexisting rocks (clastic rocks) • Sandstone • Shale – Skeletal debris • Limestone – Chemical precipitates • Evaporates 13 Sedimentary Rocks • Stratum: – Tabular layer of sediment accumulated in discrete episodes – Bed 14 Metamorphic Rocks • Formed by alteration of preexisting rocks under high temperatures and pressure • Alteration occurs without melting rocks – Density increases – Crystals enlarge – Lineation of some minerals 15 Rock Units • Formations – Unit of rock formed in a particular way – Formally named, often for nearby geographic feature • Catskill Formation • Member – Smaller rock unit • Group – Groups of formations 16 Steno’s Principles • Principle of Superposition – Oldest strata are at the bottom in an undisturbed sequence of strata • Principle of Original Horizontality – All strata are horizontal when they form • Principle of Original Lateral Continuity – Strata originally are unbroken flat expanses – Interrupted by erosion 17 Cross-cutting Relationships • Principle of Intrusive Relationships – Intrusive igneous rocks are always younger than the rock they invade • Principle of Components – Fragments within a second body of rock are older than the second body of rock 18 Fossils • Remnants of ancient life, thousands to millions of years old • Fossil succession – Date by comparing them to fossils throughout the world – William Smith 19 Unconformity • Substantial interval of time when erosion occurred rather than deposition 20 Unconformity – Angular unconformity – Disconformity – Nonconformity 21 Angular Unconformity 22 Geologic Time Scale • Developed using – Biostratigraphy (fossil succession) – Radioactive decay • Divided into – Phanerozoic – Precambrian/Archean • Cambrian – Oldest rocks with conspicuous fossils See p. 12 23 Earth’s Interior • Crust • Mantle • Core – Mohorovicic Discontinuity (Moho) • Crust/mantle boundary • Lithosphere • Asthenosphere 24 Plate Tectonics • Crust – Oceanic • Mafic (Mg- and Fe- rich) – Continental • Felsic (Si-rich, lower in Mg and Fe) 25 Plate Tectonics • Movement of lithospheric plates • Plates formed at spreading centers, destroyed at trenches • Driven by convection 26 27 Convection • Material heated deep in asthenosphere rises to displace cooler less dense material nearer the surface 28 Spreading Zones • Plates move apart • Mid-ocean ridge 29 The land of fire and ice Mid-Atlantic Ridge, a spreading zone 30 Subduction Zones • Trenches • Associated with volcanoes – Partial melting of lithosphere Animations 31 32 Hydrological (Water) Cycle • Water – Abundant – High heat capacity • Water cycle – Exchange between reservoirs • • • • Atmosphere Biosphere Hydrosphere Groundwater 33 Evolution • The process by which particular forms of life give rise to other forms by way of genetic changes. • Natural selection – Primary mechanism of evolution – Process operates on heritable variability, selection results from differences among individuals in longevity and production of offspring • Extinction • Mass extinctions – Global catastrophes in which large percentage of species disappeared 34 The Six Mass Extinctions 1 3 2 5 4 6 35 Directional Changes in Earth’s History •Initial views of Earth •Internal energy •Solar energy •Evolution of life •Life shapes environment and vis versa (reducing to oxydizing atmosphere Episodic changes (External and Internal causes) •Asteroid impacts •Milankovitch •Earthquakes •Sedimentation •Extinctions 36