Inside the Earth Pgs 88 - 94
What’s Inside • The Earth is not just solid rock, it is made of layers. • Each layer is has its own composition and properties. • These include things like element type, temperature, density and ability to flow.
The Crust • Earth’s outermost layer is the crust. • The crust is 5 to 100km thick and is the thinnest layer. • Two types of crust exist: continental and oceanic. • Continental crust is similar to granite and has an average thickness of 30 km. • Oceanic crust is similar to basalt and is 5-8km thick • Basalt is denser than granite and so oceanic crust is denser than continental.
The Mantle • The middle layer of the Earth is the mantle. • The mantle is the thickest layer, about 2,900km thick, and contains most of the Earth’s mass. • It is made of lots of iron and magnesium. • No one has seen the mantle, and so scientists must hypothesize what it looks like. • They look at the ocean floor to get an idea of what it might be. • Underwater volcanoes and vents are like windows into the mantle.
The Core • The core is mostly made of iron with some nickel. • The core is from the bottom of the mantle to the center of the Earth. • The center of the Earth is about the size of the planet Mars. • It is only about 33% of Earth’s mass and 6,856 km in diameter.
The Structure of the Earth • The Earth has five main physical layers: lithosphere, asthenosphere, mesosphere, outer core and inner core. • Each has its own set of physical characteristics.
Lithosphere (rock sphere) • It is the outermost rigid layer of the Earth. • It is made of crust and the rigid upper part of the mantle. • It is divided into separate pieces called tectonic plates.
Asthenosphere (weak sphere) • It is a soft layer of the mantle on which pieces of the lithosphere move. • It is made of solid rock that flows slowly like putty.
Mesosphere (middle sphere) • It is below the asthenosphere and extends down to the Earth’s core. • It is the largest layer that is about 2550 km thick.
Outer Core and Inner Core • The outer core is the liquid layer of the Earth’s core that lies beneath the mantle and surrounds the inner core. • The inner core is the solid dense center of our planet that extends from the bottom of the outer core to the center of the Earth.
Tectonic Plates • The Earth is broken into several tectonic plates that fit into each other like a giant jigsaw puzzle. • Tectonic plates can have oceanic crust, continental crust or both. • Similar to icebergs, tectonic plates have much more material below the surface than above the surface.
Mapping the Earth’s Interior • How do we know what the core and mantle are made of? • Earthquakes • When an earthquake occurs, vibrations called seismic waves are produced and travel through the Earth. • We can measure the speed at which the wave travels and the speed will vary with the material it travels through.
Measuring waves • A wave will travel quicker through a solid than a liquid. • A seismic wave will slow down when traveling between the mesosphere and the outer core because it goes from a solid to a liquid. • We use a seismograph to measure seismic waves and record them. • Scientists use these measurements to calculate the thickness of each layer of the Earth.