Chapter 22.1: Earth’s Structure What is geology? What are the characteristics of Earth’s three layers?

Geology = The study of the planet Earth’s composition & structure How do we know about Earth’s interior if we can’t see it? Interpret seismic (earthquake) waves Waves travel at different speeds in different mediums and materials

2 Forces that Change Earth’s Surface A. Constructive Forces = Forces that build up mountains etc. B. Destructive Forces = Forces that slowly wear away any feature

Uniformitarianism The idea that geological process that operate today also operated in the past. Ancient rocks formed under the same situations as current geological processes.

Earth: Cross Section Major Layers 1. Core (inner and outer) 2. Mantle 3. Crust Why does Earth have layers? Most dense material sinks to center / Light stuff “floats” on top Temperature and pressure increase with depth. Temps: Inner core (13 000 F = surface of sun); Mantle (Range fr. 7 000 – 1 600F) - Each layer varies in physical properties: density, temp., ability to flow (viscosity)

Core Mantle Crust Sulfur (4%) Nickel (11%) Iron (85%) Density: ~3 g/cm3 Density: ~5 g/cm3 Density: ~11 g/cm3

The Composition of the Earth The Earth is made of many different and distinct layers. The deeper layers are composed of heavier materials; they are hotter, denser and under much greater pressure than the outer layers.

Crust Composition Light Rock layer Thin layer Made of silicates (Light rocks of silicon & oxygen) Types of Crust A. Continental Less dense rocks like granite 8 – 40 km thick Older B. Oceanic Dense rocks like basalt ~7 km thick Younger

Abundances of Elements in Earth’s Crust Silicon & Oxygen compounds = silicates ( ~ 74%) These make crust light!

“Moho” = boundary b/w crust & upper mantle

The Mantle Composition: Hot Heavy Rock! Made of silicates; but also a lot of iron & magnesium (heavier) Temps: 1,600  7,000 F Pressure increases as you descend! Not COMPLETELY solid Middle part is “plastic”/ taffy like Hot rock moves in CONVECTION CURRENTS

3 Divisions of the Mantle Lithosphere = Upper mantle + Crust “Plates”, Rigid Slabs Asthenosphere = Softer, moving hot rock (Convection Currents) Mesosphere = Stiffer rock near core

How do we know what’s in the mantle? How do we know what it is made of? Scientists infer based on: Pushed up rock Ocean floor/molten rock Seismic waves What is it like? Like the mineral olivine Large amounts of iron and magnesium

Core Composition: Heavy Metals! Iron & Nickel (How do we know? Earth’s magnetic field & seismic waves) Pressure 3.6 million times that at surface Temps: 6 700 C (same as surface of sun)

2 Layers of Core Inner Core Outer Core Solid iron and nickel High pressure keeps it solid Outer Core Liquid iron and nickel High temp. keeps it liquid Responsible for Earth’s magnetic field

Iron (85%) Nickel (11%) Sulfur (4%) Density: ~11 g/cm3 The Core

Upper mantle Label Each Layer. Be able to describe each layer.

Self Quiz Compare how constructive and destructive forces affect Earth’s surface. List the 3 layers of Earth. Which layer has currents of moving rock? Which is the most dense layer? Which layer is made of light rocks like silicates? Which is more dense: Continental or Oceanic Crust? Which layer of the mantle is part of Earth’s plates? Which layer is made of heavy metals?

Answers to Self Quiz Constructive forces build new land/crust and destructive forces destroy crust. Crust, Mantle, Core The asthenosphere – which is in the mantle The core The crust Oceanic crust is denser (but thinner) The upper mantle (and the crust make up the lithosphere, or plates) Core