What Are Earth’s Layers

Unit D, Chapter 1, Lesson 1, pD6-11

Earth’s Layers

• Where does information about Earth’s structure come from?– Drills• Samples taken from first 10-12 km

– Hypothesis• Patterns of earthquake waves traveling through Earth• Materials that come out of active volcanoes

Seismic Waves Pattern in Earth with no layers

Pattern of Seismic Waves in Earth with layers

Earth’s Layers• Crust: Earth’s outermost layer– Continental crust made of granite

• Less dense– Oceanic crust made of basalt

• More dense

• Mantle: layer directly below the crust– 1600°C at the top and 4000°C at the bottom

• Hot enough to melt rock– Solid rock

• Intense pressure pushes rock into a solid• Only upper mantle is partly melted

Earth’s Layers

• Core: innermost layer– Outer core• Hot, liquid iron and nickel

– Inner core• Hotter than 5500°C

– Hot enough to melt metal

• Solid iron– Intense pressure pushes metal into a solid

Earth’s Layers

• Zones– Lithosphere• Includes all crust and part of upper mantle• Cool, solid part of Earth

– Lithos- Greek for “stone”

– Asthenosphere • Part of the upper mantle• Partly melted rock in upper mantle

– Asthenes- Greek for “weak”

Earth’s Plates• 7 major lithospheric plates

– Float on asthenosphere – partly melted rock• Plasticity: it can flow (like silly putty)• Convection currents in asthenosphere caused by heat from Earth’s

center– Hot mantle Less dense hot mantle pushed up by more dense cooler rock– Hot rock spreads out & cools– Cooler, more dense rock sinks

• Lithospheric plates move asthenosphere flows– Plates constantly move– A few centimeters each year

• Lithospheric plates constantly change in shape and size– Plates slit across new lines– Combine with other plates– Slide under another plate to become mantle rock again

• Earthquakes and volcanoes usually found at plate boundaries

Earth’s Plates• Major plates names after continents or oceans they carry

– North American Plate: • North America & Atlantic Ocean

– South American Plate: • South America & Atlantic Ocean

– Australian-Indian Plate: • Australia, India, & Indian Ocean

– Antarctic Plate: • Antarctica & Pacific, Atlantic, & Indian Oceans

– Pacific Plate: • Pacific Ocean

– African Plate: • Africa & Atlantic & Indian Oceans

– Eurasian Plate: • Europe & Asia & Atlantic Ocean

Earth’s Plates

• Plate tectonics: theory scientists use to explain plate movements– Tectonics Greek word meaning “builder”• Plate movements build Earth’s largest landforms

– Plates move, break apart, collide

Earth’s Plates

• Most plates contain both oceanic and continental crust– Oceanic crust• Newer, thinner, under oceans

– Continental crust• Older, thicker, land

Changes to Earth’s Surface

• Earth’s surface is constantly being changed– Movement of plates• Move continents around the globe

– Form mountains– Causing earthquakes & volcanic eruptions

– Erosion and deposition• Water and wind erosion carve out valleys, cliffs, and

caves• Rivers deposit sand and rock on its banks & at mouth• Wind picks up sand and deposits it on dunes

Changes to Earth’s Surface• Earth’s surface is constantly being changed– Glaciers

• Erodes land and deposits rock, sand, and mud– Rocks & pebbles pulled by glacier act like sandpaper

» Gravity pulls glacier downhill– Glaciers melt and deposit material

» Form ridges, hills, gravel-covered plains

– Objects from space• Meteoroids – chunks of rock moving through solar system

– Enter Earth’s atmosphere– Friction causes it to heat-up & burn

» Meteor = streak of light, “shooting star”» Meteorite = meteoroid that hits the ground» Most too small to notice

• Comets & asteroids

Summary

• Earth is composed of inner core, outer core, mantle, & crust– Lithosphere = crust + part of upper mantle

• Theory of plate tectonics explains how lithospheric plates move causing changes to Earth’s surface

• Other changes to Earth’s surface caused by:– Wind & water– Glaciers– Space objects that hit Earth

Homework

• Read Unit D, Chapter 1, Lesson 1, pD6-11• Answer ?s on Google form