Chapter 1 Earth System History

Earth System History Study of the inter- connected physicochemical and biological changes that our planet has experienced over the course of geologic time

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?

Earth Systems History Earth is an Archive Geologic record archives Earth’s history Interaction of complex systems within the planet

Foundations of Geology James Hutton Principle of Uniformitarianism There are inviolable laws of nature that have not changed in the course of time First founding principle of geology Actualism Application of modern processes to ancient system Popularized by Charles Lyell Charles Lyell

Actualism Modern ripples provide clues to ancient systems.

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

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

Rock Cycle Surface and internal processes link materials to form three rock types: Igneous Sedimentary Metamorphic

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

Igneous Rocks Extrusive igneous rocks Intrusive igneous rocks harden at the earth’s surface Intrusive igneous rocks harden within the earth

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

Sedimentary Rocks Formed from: Preexisting rocks (clastic rocks) Sandstone Shale Skeletal debris Limestone Chemical precipitates Evaporates

Sedimentary Rocks Stratum: Tabular layer of sediment accumulated in discrete episodes Bed

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

Rock Units Formations Member Group 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

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

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

Fossils Remnants of ancient life, thousands to millions of years old Fossil succession Date by comparing them to fossils throughout the world William Smith

Unconformity Substantial interval of time when erosion occurred rather than deposition

Unconformity Angular unconformity Disconformity Nonconformity

Angular Unconformity

Geologic Time Scale Developed using Divided into Cambrian Biostratigraphy (fossil succession) Radioactive decay Divided into Phanerozoic Precambrian/Archean Cambrian Oldest rocks with conspicuous fossils See p. 12

Earth’s Interior Crust Mantle Core Lithosphere Asthenosphere Mohorovicic Discontinuity (Moho) Crust/mantle boundary Lithosphere Asthenosphere

Plate Tectonics Crust Oceanic Continental Mafic (Mg- and Fe- rich) Felsic (Si-rich, lower in Mg and Fe)

Plate Tectonics Movement of lithospheric plates Plates formed at spreading centers, destroyed at trenches Driven by convection

Convection Material heated deep in asthenosphere rises to displace cooler less dense material nearer the surface

Spreading Zones Plates move apart Mid-ocean ridge

Mid-Atlantic Ridge, a spreading zone The land of fire and ice Mid-Atlantic Ridge, a spreading zone

Subduction Zones Trenches Associated with volcanoes Partial melting of lithosphere Animations

Hydrological (Water) Cycle Abundant High heat capacity Water cycle Exchange between reservoirs Atmosphere Biosphere Hydrosphere Groundwater

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

The Six Mass Extinctions 1 3 5 4 6 2

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