Geology 105 Lecture Notes

Geology 105 Lecture Notes - Geology 105 Lecture Notes Three...

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Geology 105 Lecture Notes Three Unifying Themes of ELTT 1. Earth is a system of interacting components a. System: group of interacting objects, organisms, and processes b. Made of reservoirs interconnected by fluxes of matter and energy 2. Plate Tectonics is the unifying theory of geology 3. The Earth system is changing or evolving over time Most of the Earth’s surface in two elevation zones - Continent interior and shelves within 1 kilometer of sea level - Ocean floor 4-5 km below sea level - High mountains deep ocean trenches occupy small area James Hutton and Principle of Uniformitarianism - The Earth today is begin shaped by processes we can observe in operation today - Structures and textures in ancient rocks record operation of same processes that make similar features in loose sediment, today - “The present is the key to the past” Present is the Key to the Past - Observe process of formation of structures in modern sediment - Interpret similar structures in “ancient” sedimentary rocks as having same origin - Mud cracks form when shallow muddy bottom dries out o Recorded on ancient mudrock bedding plane - Cross-bedding is signature of wind-blown sand o Identify ancient sand dunes Uniformitarianism and the Age of the Earth – or – Why the Earth Must be Very Old - Ancient sedimentary rocks formed by accumulation of sand or mud, layer by layer
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- Modern mud and sand are observed to accumulate slowly o 1mm/yr to 1 m/yr - Total thickness of strata on continents > 100,000 m - Time needed to accumulate more than 100 Ma (million annum or millions of years) Discovering the Earth’s Structure – “Peeling the Onion” - We study the Earth from the “outside, in” - Interior probed by earthquake waves o Crust, mantle, core - Meteorites – fragments of planetary interior from asteroid belt – are these what the Earth’s core and mantle are made of? Processes – Instantaneous and gradual - 1500 meters of strata accumulating at 1mm/year needs 15 Ma Structure of the “Lithosphere” – “Rocky Shell” - Lithosphere = Crust + rigid upper mantle 70-150 km thick - Thin (5 km) Oceanic Crust o Formed of basalt erupted along spreading midocean ridges - Thick (35-65 km) Continental crust
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Geology 105 Lecture Notes - Geology 105 Lecture Notes Three...

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