Download Anyone who has attended elementary school knows Earth is layered

Content Benchmark E.8.C.3
Students know Earth is composed of a crust (both continental and oceanic); hot convecting
mantle; and dense, a metallic core. E/S
Anyone who has attended elementary school knows Earth is layered. Most can even identify the
layers as; inner core, outer core, mantle, and crust. But rarely can one answer the following
questions:
What is each layer of the earth made of?
What is going on in each layer of the Earth?
How do we know about all the layers of Earth?
Although the interior of Earth is only ~40km beneath our feet, it is more difficult to reach than
the moon! Twelve kilometers is as deep as anyone has ever dug underneath Earth’s surface. So,
how do we know that Earth has four layers and each layer is made of different materials? It is
these questions that scientists try to find answers to using both direct and indirect science
processes. Current information comes from studying earthquake waves travelling through the
Earth, as well as from laboratory experiments on surface minerals and rocks at high pressure and
temperature.
Earth’s Structure
Figure 1. Layered Earth
(From http://www.dailygalaxy.com/photos/uncategorized/2007/06/29/earths_core_2.gif)
Earth is composed of three basic layers; core, mantle, and crust. The core represents 15% of
Earth’s volume, the mantle 84%, and the crust only 1%. Each of the layers is unique in what
materials compose it, specifically in regards to density, temperature, and unique properties. Let’s
use diagrams to give a detail description of each layer of Earth.
The Crust
Figure 2. This diagram shows the crust in relation to other layers and depicts the
differences between continental and oceanic crust.
(From http://www.vulkaner.no/v/vulkinfo/tomtech/etomtech.html)
Sometimes compared to the skin of an apple or peach, Earths’ crust is the thinnest layer. It is
composed of two types of crustal material; continental and oceanic. Landmasses are composed
predominately of continental crustal material, while oceanic crust is the material that typically
makes up the floor of ocean basins. The main difference between the two crusts is density.
Oceanic crust is composed of thin, but dense layers of Basaltic material. Its average density is
3.0 g/cm3. Continental crust is composed of thick, but less dense rock, mainly Granite. Its
average density is 2.7g/cm3. Teaching density fits well in conjunction with this benchmark.
The following resources contain information about demonstrating or calculating density:
You Are My Density, an activity that compares the differences in crust densities,
http://www.usoe.k12.ut.us/curr/science/sciber00/7th/earth/sciber/earthden.htm
Activities that are divided into two lists, grocery store “only” items, and “chemicals needed”,
http://www.elmhurst.edu/~chm/demos/index.html
Simple online activity that challenges students to calculate the density of different “types” of
blocks, can be found at http://www.edinformatics.com/math_science/density.htm
The Mantle
Figure 3. The mantle and convection currents
(From http://www.windows.ucar.edu/earth/images/convection.gif)
The Mantle is the thickest layer of the Earth and the most diverse. It has a large temperature
range, the molten material behaves differently through out, and it is responsible for the
movement of both continental and oceanic crust via convection currents. Because the mantle is
so thick, it has a large temperature difference between where it meets with the core and crust. At
its deepest parts, near the core, the temperature can reach 4000 degrees Celsius, while directly
under the crust, in the asthenosphere, the temperature is 500-900 degrees Celsius. Although
these temperatures are well beyond melting points of rock material, the mantle consists of semisolid molten rock material. The discrepancy in temperature causes the molten material to flow in
a circular pattern, called a convection cell. Convection is defined as heat transfer by the upward
movement of heated material and the downward movement of cooled material. It is caused by
differences in temperature and density.
Convection Currents
Figure 4 & 5. Convection examples
(From http://www.acer-acre.org/ClimateChangeCD/sec3/311a.htm)
For a colorful visual of how convection currents move the crustal plates and can produce both
rifting and mountain building, visit
http://education.sdsc.edu/optiputer/flash/convection.htm
For a colorful visual of convection currents in the mantel, visit
http://homepages.see.leeds.ac.uk/~eargah/Conv.html
Convection currents are the driving force of plate tectonics. Plate tectonics is the movement of
continental and oceanic crust. Earth’s crust is made up of many different plates that move
towards, away, and along side one another.
Figure 6. Plate Tectonics
(From http://www.geography-site.co.uk/pages/physical/earth/tect.html)
For additional information about plate tectonics, see
Earth Floor is a site that discusses plate tectonics in student friendly terms,
http://www.cotf.edu/ete/modules/msese/earthsysflr/plates1.html
The US Geological Services (USGS) site has links to plate tectonics and much more,
http://pubs.usgs.gov/gip/dynamic/dynamic.html
For animations explaining plate tectonics, go to
http://www.ucmp.berkeley.edu/geology/tectonics.html
The Core
Figure 7. The liquid and solid core
(From http://news.nationalgeographic.com/news/2005/08/images/050824_earthcore.jpg)
The core is often explained as two separate entities. The entire core is composed of iron and
nickel, but the inner core is solid while the outer core is liquid. The inner core is solid due to the
great pressure present at that depth beneath Earth’s surface. The origin of the Earth's magnetic
field is not completely understood, but is thought to be associated with convection in the outer
core causing the inner core to spin creating Earth’s magnetic field. The magnetic field blocks
solar wind (ionized particles from the sun) from reaching the surface of the Earth and is one of
the contributing factor in producing the Auroras (the northern and southern lights that can occur
in the night sky at extreme latitudes).
Figure 8. Earth’s magnetic field
(From http://www1.fccj.edu/pacrews/new_page_35.htm)
For more detailed information of Earth’s magnetic field, see
Student friendly descriptions of the Earth’s Magnetic field and the Van Allen Belts,
http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html
British Geological Services site that discusses the Magnetic field and the flips and reversals it
can experience, at
http://www.geomag.bgs.ac.uk/reversals.html
For illustrations and information about the Auroras, go to
http://csep10.phys.utk.edu/astr161/lect/earth/aurora.html
Content Benchmark E.8.C.3
Students know Earth is composed of a crust (both continental and oceanic); hot convecting
mantle; and dense, a metallic core. E/S
Common misconceptions associated with this benchmark
1. Students incorrectly assume that what is known about the layers of Earth was gathered
from “digging” down to the core.
Understanding Earth’s depth is very difficult for students. To confront this misconception,
students need to learn how scientists have gathered their data about the layers of Earth and
have an understanding of pressure and it effects on the melting point of materials.
Additionally, knowledge of seismic wave travel through different earth materials should be
explored.
For information on seismic waves and their relationship to Earth’s interior, go to
http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior
.html
2. Students have difficulty visualizing how semi-solid rock in the mantle flows.
Doing simple demonstrations of viscosity can help students understand how the mantle is
able to flow and create convection currents. The following sites are provided;
For a very brief activity on viscosity using Honey, visit
http://www.princeton.edu/~gasdyn/Research/T-C_Research_Folder/Viscosity_def.html
For a much more technical explanation of viscosity, visit
http://www.spacegrant.hawaii.edu/class_acts/ViscosityTe.html
For a simple explanation of how to build a viscosometer, visit
http://www.science-projects.com/Viscosity.htm
For an online application that lets student explore differences in viscosity, visit
http://www.seed.slb.com/en/scictr/lab/visco_exp/index.htm
3. Students mistakenly believe that Earth’s continents are floating on ocean water.
Looking at images showing convection currents in water and using them to explain
continental drift can fuel this misconception. When discussing oceanic and continental crust,
it is essential to show students that the crust includes both land and the ocean floor. Water is
not the division of continental crust.
To view maps showing all tectonic plates go to
http://pubs.usgs.gov/gip/dynamic/slabs.html
Content Benchmark E.8.C.3
Students know Earth is composed of a crust (both continental and oceanic); hot convecting
mantle; and dense, a metallic core. E/S
Sample Test Questions
Questions and Answers to follow on a separate document
Content Benchmark E.8.C.3
Students know Earth is composed of a crust (both continental and oceanic); hot convecting
mantle; and dense, a metallic core. E/S
Questions and Answers to follow on a separate document
Content Benchmark E.8.C.3
Students know Earth is composed of a crust (both continental and oceanic); hot convecting
mantle; and dense, a metallic core. E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark
1. 3-D models of Earth from Explorations in Earth Science
This site offers several ways to build models of Earth. Procedures for construction of a 3-D
model of the interior of the Earth, to help visualize the main layers or regions - inner core, outer
core, mantle and crust. This project enhances visualization and illustration of the relative
volumes of Earth’s layers. This activity also provides an opportunity for some practice in
problem solving and math skills.
To access this activity, visit
http://web.ics.purdue.edu/~braile/edumod/threedearth/threedearth.htm
2. How Do We Know About Layers of Earth? by ClassZone Exploring Earth
This is a great series of animations showing the layers of Earth and how waves travel through
each layer. This site can be used to clear up misconceptions about how scientists understand the
composition of the layers or as an extension for teaching wave movement. The following link
takes you to a page (Step 1) containing images of A View of Earth from Above. Below the
image are questions for discussion. “Steps” at the bottom of the page link to additional topics
directly related to this benchmark such as; 2) A View from Below, 3) Seeing with Seismology,
4) Modeling Internal Structure, 5) Locating Layers, 6) Another Model, 7) Changing the
Thickness of a Layer, 8) Structure of Earth, 9) Seismic Tomography, 10) Beneath the Surface,
and 11) Find Out More About Seismic Tomography.
To access these animations, visit
http://www.classzone.com/books/earth_science/terc/content/investigations/es0402/es0402page01
.cfm
3. Convection Currents
There are a variety of ways to create convection in the classroom. However, if using a flame or
hot plates is a safety issue these sites offer visual representations, simulations, and movies of
convection.
Educators Guide to Convection from Jet Propulsion Laboratory contains convection animations
and videos and can be accessed at
http://www.solarviews.com/eng/edu/convect.htm
This animation shows a cross section of Earth; it illustrates a mathematical model of how
convection might occur in the mantle. Diagrams of convection cells in the mantle are often
highly simplified, but researchers are finding that the real world is much more complex.
To access this animation, visit
http://www.classzone.com/books/earth_science/terc/content/visualizations/es0805/es0805page01
.cfm