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Chapter 1

Earth System History

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Earth System History

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

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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?

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Earth Systems History

• Earth is an Archive– Geologic record archives Earth’s

history– Results from the interaction of

complex systems within the planet

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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

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Actualism

• Modern ripples (A) provide clues to ancient systems (B)

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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

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Rock Cycle

• Surface and internal processes link materials to form three rock types: – Igneous– Sedimentary– Metamorphic

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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

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Igneous Rocks• Extrusive igneous rocks

– Hardens at the Earth’s surface

• Intrusive igneous

rocks– Hardens within

the Earth

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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

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• Formed from: – Pre-existing rocks

• Sandstone• Shale

– Skeletal debris• Limestone

– Chemical precipitates• Evaporates

Sedimentary Rocks

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Sedimentary Rocks

• Stratum: – Tabular layer

of sediment accumulated in discrete episodes

– Bed

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Metamorphic Rocks

• Formed by the alteration of preexisting rocks under high temperatures and pressure

• Alteration occurs without melting rocks

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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

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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

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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

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Fossils

• Remnants of ancient life, thousands to millions of years old

• Fossil succession– Date by comparing

them to fossils throughout the world

– William Smith

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Geologic Time Scale

• Developed using – Biostratigraphy (fossil succession)– Radioactive decay

• Divided into– Phanerozoic– Precambrian/Archean

• Cambrian– Oldest rocks with conspicuous

fossils

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Earth’s Interior

• Crust• Mantle• Core

– Moho• Crust/mantle boundary

• Lithosphere• Asthenosphere

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Plate Tectonics

• Crust– Oceanic

• mafic

– Continental• felsic

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Plate Tectonics• Movement of

lithospheric plates

• Plates formed at spreading centers, destroyed at trenches

• Driven by convection

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Convection

• Material heated deep in the asthenosphere rises to displace cooler, denser material nearer the surface

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Spreading Zones

• Plates move apart

• Mid-ocean ridge

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Subduction Zones

• Trenches• Associated

with volcanoes– Partial

melting of upper mantle

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Water Cycle• Water

– Abundant– High heat capacity

• Water cycle– Exchange between

reservoirs• Atmosphere• Biosphere• Hydrosphere• Groundwater

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Directional Changes

• Evolution- the changing of organisms that constitute

biosphere is a one-way process.

• Cooling - the Earth’s internal temperature is slowly decreasing.

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Unconformity

• Substantial interval of time when erosion occurred rather than deposition

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Unconformity

– Angular unconformity– Disconformity– Nonconformity

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Evolution

• Extinction

• Mass extinctions– Global catastrophes in which a large

percentage of species disappeared