EARTH’S INTERNAL STRUCTURE And processes

What Was Early Earth Like?  Describe what Earth was like right as the Solar System was forming?  Why did earth get hot?  What do fluids do when they are hot?  At first there were no layers, where did they come from?

Early Earth  Early Earth was homogeneous (uniform)  Composed of mostly silicates, iron and magnesium oxides  Temperature increased because of:  Meteorite impacts  Gravitational Compression  Radioactive Decay  When Iron and Nickel melted everything changed.

Earth’s Differentiation  Differentiation = segregated into a series of concentric layers of differing composition and density  Molten iron and nickel sank to form the core  Lighter silicates flowed up to form mantle and crust

Distinct Layers  Crust  Mantle  Core  Lithosphere  Asthenosphere  Lower Mantle  Outer Core  Inner Core Compositional LayersMechanical Layers

Crust  2 types  Continental Crust 20km ~ 90km thick (12~56miles) Density of 2.7g/cm 3  Oceanic Crust 5km ~ 10km thick (3~6miles) Density of 3g/cm 3  If the earth were an inflated balloon, the crust would be the skin!  What element do you think makes up most of the crust?

Crust  Oxygen is the most common element in the crust!  Oxygen bonds with the other elements to make minerals of the crust. The crust is not just oxygen!

Crust  Continental crust is made up of all rock types.  In general it is where you find less dense minerals  More pores (spaces) in the rocks further decrease density  Oceanic crust made of more dense rocks.  The minerals have a higher amounts of iron and magnesium  Smaller pores means higher density

Mantle  Mantle is about 2,885km thick! About 1800miles.  The mantle is SOLID ROCK, it is not a liquid!  Has a density from about 3.5g/cm 3 to 5.5g/cm 3  Lets think about that for a second!!!

Mantle  But, if the mantle is SOLID how can it flow?  At about 100km – 150km it is hot enough to flow very slowly.  The mantle makes up about 83% of earth’s total volume.  It is made up almost entirely by a iron and magnesium rich, dark colored rock, called Peridotite.

Core  The core is made up of iron alloy (iron mixed with small amounts of other elements)  Outer core is about 2255km thick. About 1400miles  Outer core is liquid because temperature is so high that not even the high pressure can force it to become solid.  Inner core is about 1220km thick. About 758miles.  Even though it is hotter than the outer core, the pressure is so high that the atoms get forced together to make a solid.

Core  The swirling convective flow in the outer core creates earth’s magnetic field.  The Inner core actually spins slightly faster than the rest of the planet due to the force of earth’s magnetic field.

Lithosphere and Asthenosphere  So far we have broken the layers down by composition and density. (Crust, Mantle, Core)  We can also divide them up by how they “behave”  The upper most layer is called the lithosphere  It is rigid, meaning it can bend slightly but not flow at all.  This layer extends down from the surface about km.  What two compositional layers does this include?  Do lithosphere and crust mean the same thing?

Lithosphere and Asthenosphere  Below the lithosphere you have the asthenosphere  The asthenosphere is entirely upper mantle rock  It is NOT A LIQUID!  But it is hot enough, 1280°C or 2330°F, that it can flow very slowly.  Even at that temp. it can only flow about 10cm – 15cm per year.

Earth’s Interior Layers Lithosphere –solid upper mantle and crust Asthenosphere –part of upper mantle –behaves plastically and slowly flows –broken into plates that move over the asthenosphere

Plate Tectonic Theory  Lithosphere is broken into individual pieces or plates Plates move over the asthenosphere –as a result of underlying convection cells

Modern Plate Map

Summary  Earth has layers because of density.  As you go towards the center temp and pressure increase.  You can refer to earths Compositional Layers –or- its Mechanical Layers