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 rocks 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 – Results from the 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 • James Hutton • Actualism – Application of modern processes to ancient system • Catastrophism 5 Actualism • Modern ripples (A) provide clues to ancient systems (B) 6 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/Exposure – Rocky surfaces that stand exposed and are readily accessible for study 7 Rock Cycle • Surface and internal processes link materials to form three rock types: – Igneous – Sedimentary – Metamorphic 8 Igneous Rocks • Formed by cooling of molten material to the point of hardening – Composed of interlocking grains, each consisting of a particular mineral • Magma – Molten material that solidifies into igneous rock 9 Igneous Rocks • Extrusive igneous rocks – Hardens at the Earth’s surface • Intrusive igneous rocks – Hardens within the Earth 10 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 11 Sedimentary Rocks • Formed from: – Pre-existing rocks • Sandstone • Shale – Skeletal debris • Limestone – Chemical precipitates • Evaporates 12 Sedimentary Rocks • Stratum: – Tabular layer of sediment accumulated in discrete episodes – Bed 13 Metamorphic Rocks • Formed by the alteration of preexisting rocks under high temperatures and pressure • Alteration occurs without melting rocks 14 Rock Units • Formations – Unit of rock formed in a particular way – Formally named, often for nearby geographic feature • Kaibab Limestone (Rim of the Grand Canyon) • Member – Smaller rock unit • Group – Groups of formations 15 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 16 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 17 Fossils • Remnants of ancient life, thousands to millions of years old • Fossil succession – Date by comparing them to fossils throughout the world – William Smith 18 Geologic Time Scale • Developed using – Biostratigraphy (fossil succession) – Radioactive decay • Divided into – Phanerozoic – Precambrian/Archean • Cambrian – Oldest rocks with conspicuous fossils 19 Earth’s Interior • Crust • Mantle • Core – Moho • Crust/mantle boundary • Lithosphere • Asthenosphere 20 Plate Tectonics • Crust – Oceanic • mafic – Continental • felsic 21 Plate Tectonics • Movement of lithospheric plates • Plates formed at spreading centers, destroyed at trenches • Driven by convection 22 Convection • Material heated deep in the asthenosphere rises to displace cooler, denser material nearer the surface 23 Spreading Zones • Plates move apart • Mid-ocean ridge 24 Subduction Zones • Trenches • Associated with volcanoes – Partial melting of upper mantle 25 Water Cycle • Water – Abundant – High heat capacity • Water cycle – Exchange between reservoirs • • • • Atmosphere Biosphere Hydrosphere Groundwater 26 Directional Changes • Evolution - the changing of organisms that constitute biosphere is a one-way process. • Cooling - the Earth’s internal temperature is slowly decreasing. 27 Unconformity • Substantial interval of time when erosion occurred rather than deposition 28 Unconformity – Angular unconformity – Disconformity – Nonconformity 29 Evolution • Extinction • Mass extinctions – Global catastrophes in which a large percentage of species disappeared 30