1. How the Earth Works: A Peek Inside Earth’s Interior - The first thing to remember is that NOBODY has ever been there! - Depending on the temperature and depth, a particular Earth material may behave like a brittle solid, deform in a plastic–like manner, or melt and become liquid. First, let’s take a big-picture look at what we are talking about. - Last week, we discovered that movement inside the Earth causes the surface of the Earth to be habitable. Today, we are going to use our knowledge of temperature, pressure, and density to learn how the inside of the Earth moves.

2. (1 mile = 1.609344 km)

3. -What we think we know comes from a study of how earthquake (seismic) waves travel through the earth, and how long it takes for them to get from where the earthquake happens to a recording station. -The basic idea is that different materials transmit seismic waves at different speeds. With a lot of earthquakes and a lot of recording stations, geophysicists are beginning to get a pretty detailed picture of what is probably down there. How the Earth Works: How Do We Know What We Know?

4. -One of the most distinctive features of the earth's interior is how it seems to be layered by density, with the heaviest stuff in the center, and the lightest material at the surface. The earth probably looks a lot like a hard boiled egg if you could cut it open. - The yellow stuff in the center (the yolk) relates to what we call the core. Most geophysicists think that the core is composed of high density materials like iron and nickel. The core is split into two subcategories: a solid core surrounded by a liquid core. - The egg's shell is like the earth's crust - a thin veneer of rigid, low density material at the surface. - And all the white stuff in between is like the earth's mantle - the largest layer which, in the case of the earth, is of medium density. The mantle is split into two subcategories: the upper and lower mantle. How the Earth Works: All Cracked Up

5. Eggs-ellent Quick Lab

6. How the Earth Works: The Core -Earth's core is thought to be composed mainly of an iron and nickel alloy. This composition is assumed based upon calculations of its density and upon the fact that many meteorites (which are thought to be portions of the interior of a planetary body) are iron-nickel alloys. -The core is earth's source of internal heat because it contains radioactive materials which release heat as they break down into more stable substances. - The core is divided into two different zones. The outer core is a liquid because the temperatures there are adequate to melt the iron-nickel alloy. However, the inner core is a solid even though its temperature is higher than the outer core. Here, tremendous pressure, produced by the weight of the overlying rocks is strong enough to crowd the atoms tightly together and prevents the liquid state.

7. Inner core  Sphere with a radius of 3486 kilometers (2161 miles)  Material is stronger than the outer core  Behaves like a solid Outer core  Composed mostly of an iron- nickel alloy  Liquid layer  2270 kilometers (1410 miles) thick  Convective flow within generates Earth’s magnetic field How the Earth Works: More about the Core

8. -Earth's mantle is thought to be composed mainly of olivine-rich rock. It has different temperatures at different depths. The temperature is lowest immediately beneath the crust and increases with depth. The highest temperatures occur where the mantle material is in contact with the heat-producing core. -This steady increase of temperature with depth is known as the geothermal gradient. The geothermal gradient is responsible for different rock behaviors and the different rock behaviors are used to divide the mantle into two different zones. -Rocks in the upper mantle are cool and brittle, while rocks in the lower mantle are hot and soft (but not molten). Rocks in the upper mantle are brittle enough to break under stress and produce earthquakes. However, rocks in the lower mantle are soft and flow when subjected to forces instead of breaking. How the Earth Works: The Mantle

9. How the Earth Works: More about the Mantle Lower mantle (near the core)  Rigid layer between the depths of 660 kilometers and 2900 kilometers  Rocks are very hot and capable of very gradual flow Lithosphere (crust and upper mantle)  Earth’s outermost layer Relatively cool, rigid shell  Averages about 100 kilometers in thickness, but may be 250 kilometers or more thick beneath the older portions of the continents Asthenosphere (bottom of upper mantle)  Beneath the lithosphere, in the upper mantle to a depth of about 600 kilometers  Small amount of melting in the upper portion mechanically detaches the lithosphere from the layer below allowing the lithosphere to move independently of the asthenosphere

10. How the Earth Works: The Crust - There are two different types of crust: thin oceanic crust that underlies the ocean basins and thicker continental crust that underlies the continents. - These two different types of crust are made up of different types of rock. The thin oceanic crust is composed of primarily of basalt and the thicker continental crust is composed primarily of granite. The low density of the thick continental crust allows it to "float" in high relief on the much higher density mantle below.

11. How the Earth Works: More about the Crust -The crust of Earth is divided into two types: oceanic and continental. - Most oceanic crust is composed of the rock basalt. Basalt is mafic (which means it has a high magnesium and iron content), composed of the minerals: calcium-rich plagioclase feldspar, olivine, amphibole, and pyroxene. Continental crust has more range in composition, but its average composition is similar to the rock granite. Granite is a felsic rock (which means it has a high feldspar and silica content), composed of quartz, potassium-rich feldspar, and mica. Mafic rocks contain denser minerals and therefore, oceanic crust is denser than continental crust (the average density of basalt is 3.0 g/cm 3 and granite is 2.7 g/cm 3 ). On average, continental crust is much thicker and older than oceanic crust.

12. Rock Examples

14. -There are two different theories about how Earth’s mantle moves. One theory says that the upper mantle and lower mantle move together as a single convection system. -Another theory states that the asthenosphere has its own convection system separate from the rest of the mantle. There is good evidence for both of the explanations. As with any scientific debate, more research and evidence must be presented before anyone can say for sure which theory is correct. How the Earth Works: A Peek Inside Earth’s Interior -What we DO know is the interior of the Earth is hot! The core heats up the lower mantle, which becomes less dense and rises to the upper mantle where it comes in contact with cooler material. -The warmer material loses heat and the cooler material gains heat until both are the same temperature. As the resulting material cools, it becomes denser and sinks back to the lower mantle. The temperature of the material is then increased by the heat inside the Earth, decreasing density and rising again. This results in convection cells that transfer heat and create movement inside the Earth.

15. How the Earth Works: Convection Currents Safety First! Convection Lab

16. Where do you think there is evidence of convection currents in your home? In a two-story building, where do you think it is warmer? Why? Where would you want to have heater vents in your home? Why? What would happen if the heater vents were located near the ceiling instead? How the Earth Works: Convection in Your Daily Life

17. Next week: Plate Tectonics! Please read Chapter 15 of your textbook for Monday. Also, don’t forget your 1 st Quarter Homework is due Wednesday, Sept. 14 (the beginning of class). Announcements