1. The Layers of the Earth!

3. Earth Layers The Earth is divided into four main layers. *Inner Core
*Outer Core
*Mantle
*Crust

4. The Crust
* The Earth’s crust is like the skin of an apple. It is very thin compared to the other three layers.
*The crust makes up 1% of the Earth.
* The crust of the Earth is broken into many pieces called plates.

5. The Mantle The mantle is the layer below the crust.
The mantle is the largest layer of the Earth.
The mantle is divided into two regions: the upper and lower sections.

6. Outer Core * The core of the Earth is like a ball of very hot metals.
* The outer core is liquid.
* The outer core is made up of iron and is very dense.

7. Inner Core
* The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move.
* The inner core is a solid.

8. Convection Currents
The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over.

9. Convection Currents
The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. The crust gets a free ride with these currents, like the cork in this illustration.
Safety Caution: Don’t get your face too close to the boiling water!

10. What are the tectonic plates?
VIDEO LECTURE Tectonic Plates and Brittle vs Ductile in:
There is widespread confusion between “crust” and “plates”. Unfortunately this confusion is reinforced by many popular science programs [e.g. Discovery Channel programs, etc.]). It’s not complicated is you lay this out correctly from day #1. The “plates” of plate tectonics are more correctly referred to as “lithospheric plates”. The upper portion of the lithospheric plates is Earth’s crust that is the outer rock layer of Earth chemically distinct from the underlying mantle layer. The deeper portion of the lithospheric plates is mantle material. To distinguish mantle rocks that are part of lithospheric plates from deeper, hotter, and therefore weaker mantle rocks, the term “lithospheric mantle” is sometimes used for the mantle that makes up the deeper part of plates. Total thickness of lithospheric plates is about 100 km. Compared to deeper layers of Earth, lithospheric plates are colder, more rigid, and much more brittle (capable of breaking when large forces are applied). The mantle below the plates is called “asthenosphere” or “asthenospheric mantle”. This part of the mantle is not liquid but it is close to its melting temperature. It is therefore capable of flowing (at very slow rates) if forces are applied for long times. Silly putty is a useful analog to the mechanical behavior of the asthenosphere.
Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication.
You can find this at .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes;
AKA: Lithospheric plate
The ~100-km-thick surface of the Earth;
Contains crust and part of the upper mantle;
It is rigid and brittle;
Fractures to produce earthquakes.

11. The Lithosphere
The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.

12. The Lithospheric Plates
The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere.

13. What is the asthenosphere?
USGS Graphics
Asthenosphere:
Is the hotter upper mantle below the lithospheric plate;
Can flow like silly putty; and
Is a viscoelastic solid, NOT liquid!!
Watch the Video to learn “common misconceptions”: Asthenosphere There is also confusion about the asthenosphere. It is not liquid and the plates do not glide over it like a sheet of water. It is hot but not hot enough to melt the rocks because it is under intense pressure from the overlying rocks. But there is melt and it is not brittle. It is what we call a viscoelastic solid. It can deform and flow over a long interval of time, therefore a good analog is silly putty which will stretch and deform when pulled slowly.
Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication.
You can find this at .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes;

14. The Crust
The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates.

15. The Structure of the Earth and Plate Tectonics

16. Structure of the Earth The Earth is made up of 3 main layers: Core
Mantle
The Earth is made up of 3 main layers:
Core
Mantle
Crust
Outer core
Inner core
The interior of the Earth is divided into layers based on chemical and physical properties.
The Earth has an outer silica-rich, solid crust, a highly viscous mantle, and a core comprising a liquid outer core that is much less viscous than the mantle, and a solid inner core.
Working from the centre of the Earth out we have:
The inner core is a primarily solid sphere about 1220 km in radius situated at Earth's center.
Based on the abundance of chemical elements in the solar system, their physical properties, and other chemical constraints regarding the remainder of Earth's volume, the inner core is believed to be composed primarily of a nickel-iron alloy, with small amounts of some unknown elements.
The temperature is estimated at 5,000-6,000 degrees Celsius and the pressure to be about 330 to 360 GPa (which is over 3,000,000 times that of the atmosphere!)
The liquid outer core is 2300 km thick and like the inner core composed of a nickel-iron alloy (but with less iron than the solid inner core).
Iseismic and other geophysical evidence indicates that the outer core is so hot that the metals are in a liquid state.
The mantle is approximately 2,900 km thick and comprises 70% of Earth's volume. (the core makes up about 30% of Earth's volume, with the outer crust [where we live] <1%!!).
The mantle is divided into sections based upon changes in its elastic properties with depth.
In the mantle, temperatures range between degrees Celsius at the upper boundary with the crust to over 4,000 degrees Celsius at the boundary with the core.
Due to the temperature difference between the Earth's surface and outer core, and the ability of the crystalline rocks at high pressure and temperature to undergo slow, creeping, viscous-like deformation over millions of years, there is a convective material circulation in the mantle (mantle convection cells). Hot material rises up as mantle plumes (like a lava lamp!), while cooler (and heavier) material sinks downward to be reheated and rise up again.
- We shall see that this process is very important for plate tectonic motion…
The outer most layer is the crust - this is the most familiar to us as it is where we live.
The distinction between crust and mantle is based on chemistry, rock types and seismic characteristics.
Presenter: Ask the students to guess what the most abundant element in the earth’s crust is…..they may be surprised to learn that it is actually Oxygen (46.6% Oxygen; 27.7% Silica; 8.1% Aluminum; 5.0% Iron; 3.6% Calcium; 2.8% Sodium; 2.6% Potassium; 2.1% Magnesium; plus trace elements)
Click to next slide for more on the Crust….
Crust

17. The Crust Continental Crust
This is where we live!
The Earth’s crust is made of:
Continental Crust
thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old
Oceanic Crust
- thin (~7 km) - dense (sinks under continental crust) - young
The Earth has two different types of crust: Continental crust and Oceanic crust. Each has different properties and therefore behaves in different ways.
Continental crust:
Continental crust forms the land (the continents, as the name suggests) that we see today.
Continental crust averages about 35 km thick. Under some mountain chains, crustal thickness is approximately twice that thickness (about 70 km thick).
- The mountains we see on earth have deep roots in the crust that we can’t see. The crust “floats” on the more dense mantle and, like how only the tip of an iceberg sticks up out of the water, we see only the tip of the continental crust - the mountain ranges.
Continental crust is less dense and therefore more buoyant than oceanic crust
Continental crust contains some of the oldest rocks on Earth.
- Ancient rocks exceeding 3.5 billion years in age are found on all of Earth's continents. The oldest rocks on Earth found so far are the Acasta Gneisses in northwestern Canada near Great Slave Lake (4.03 Ga) [Ga = billion years ago] and the Isua Supracrustal rocks in West Greenland (3.7 to 3.8 Ga), but well-studied rocks nearly as old are also found in the Minnesota River Valley in the USA ( billion years), in Swaziland ( billion years), and in Western Australia ( billion years).
Oceanic crust:
As the name already suggests, this crust is below the oceans.
Compared to continental crust, Oceanic crust is thin (6-11 km).
It is more dense than continental crust and therefore when the two types of crust meet, oceanic crust will sink underneath continental crust.
The rocks of the oceanic crust are very young compared with most of the rocks of the continental crust. They are not older than 200 million years.

18. How do we know what the Earth is made of?
Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy
Acquisition: land, air, sea and satellite
Geological surveys: fieldwork, boreholes, mines
If we can’t go to the centre of the Earth (except in fictional movies!) how do we know what the internal structure of the Earth is like?
We need to use geophysical imaging techniques to model what is going on below our feet.
For example, when there is an earthquake it sends out seismic waves (shock waves) through the Earth. Seismologists can measure the time it takes for these waves to reach seismic monitoring stations set up around the globe. (The machine that measures seismic waves is called a seismometer).
The different layers in the earth have been inferred using the time of travel of refracted and reflected (bent backward angularly) seismic waves created by the earthquakes (see left diagram). That is, changes in the seismic velocity occur as the waves pass through different materials. Measuring these changes tell seismologists how many layers there are and the thickness and physical properties of each layer.
We need not wait for earthquakes to occur, on a local scale on land (cheap but slow methods) and at sea (more expensive but quicker) explosions can be set to cause shock waves to pass through the crust (simulating an earthquake) that can be measured in the same way.
Other geophysical methods, for example measuring different gravity, magnetic and electrical anomalies by air and (or) satellite can help to reconstruct shallow crustal features.
We can also go and examine rocks at and near the surface of the crust, through fieldwork, drilling boreholes and mining.

19. If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.
If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle…..the shape of Africa and South America are a good example.
This is because they DID used to fit together!
The Earth as we see it today was not always like it is now. Land masses have pulled apart and joined together by the process we call Plate Tectonics….

20. Plate Tectonics
The Earth’s crust is divided into 12 major plates which are moved in various directions.
This plate motion causes them to collide, pull apart, or scrape against each other.
Each type of interaction causes a characteristic set of Earth structures or “tectonic” features.
The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.
There are 12 major plates on Earth, each of which slide around at a rate of centimetres per year, pulling away from, scraping against or crashing into each other.
Each type of interaction produces a characteristic “tectonic feature”, like mountain ranges, volcanoes and (or) rift valleys, that we will discuss during this lecture.

21. Plate tectonics
Plates are driven by cooling of Earth (convection)
Gravity provides additional force to move plates. ? ? ?
Conceptual drawing of assumed convection cells in the mantle. Below a depth of about 700 km, the descending slab begins to soften and flow, losing its form.
Important principle: In the big picture, Earth gives off heat to cool. The heat energy from Earth’s interior produces the melt that both makes oceanic plates and moves them around on the Earth.
Convection moves hot material from Earth’s interior up to the surface to cool; gravity with convection draws the dense material back into the hotter interior; this is an efficient way for our planet to cool. In kid vernacular, “heat rises, gravity sucks.”
WHERE DOES THE HEAT COME FROM?
The heat in Earth’s interior is about 50% from formation of Earth during the development of our solar system (accretion changes gravitational potential energy to kinetic energy to heat upon impact) and 50% from decay of naturally occurring radioactive elements (principally U, Th, K). Convection cannot take place without a source of heat. Heat within the Earth comes from two main sources: radioactive decay and residual heat. Radioactive decay, a spontaneous process that is the basis of "isotopic clocks" used to date rocks, involves the loss of particles from the nucleus of an isotope (the parent) to form an isotope of a new element (the daughter). The radioactive decay of naturally occurring chemical elements -- most notably uranium, thorium, and potassium -- releases energy in the form of heat, which slowly migrates toward the Earth's surface. Residual heat is gravitational energy left over from the formation of the Earth billion years ago -- by the "falling together" and compression of cosmic debris. How and why the escape of interior heat becomes concentrated in certain regions to form convection cells remains a mystery.
The mobile rock beneath the rigid plates is believed to be moving in a circular manner somewhat like a pot of thick soup when heated to boiling.
The heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again. This cycle is repeated over and over to generate what scientists call a convection cell or convective flow While convective flow can be observed easily in a pot of boiling soup, the idea of such a process stirring up the Earth's interior is much more difficult to grasp. We know that convective motion in the Earth is much, much slower than that of boiling soup, and many unanswered questions remain: How many convection cells exist? Where and how do they originate? What is their structure?
Two activities study convection are::
Photograph: The convergence of the Nazca and South American Plates has deformed and pushed up limestone strata to form towering peaks of the Andes, as seen here in the Pachapaqui mining area in Peru. (Photograph by George Ericksen, USGS.)
Modified from USGS Graphics
Convection is like a boiling pot. Heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again.

22. What are the tectonic plates?
VIDEO LECTURE Tectonic Plates and Brittle vs Ductile in:
There is widespread confusion between “crust” and “plates”. Unfortunately this confusion is reinforced by many popular science programs [e.g. Discovery Channel programs, etc.]). It’s not complicated is you lay this out correctly from day #1. The “plates” of plate tectonics are more correctly referred to as “lithospheric plates”. The upper portion of the lithospheric plates is Earth’s crust that is the outer rock layer of Earth chemically distinct from the underlying mantle layer. The deeper portion of the lithospheric plates is mantle material. To distinguish mantle rocks that are part of lithospheric plates from deeper, hotter, and therefore weaker mantle rocks, the term “lithospheric mantle” is sometimes used for the mantle that makes up the deeper part of plates. Total thickness of lithospheric plates is about 100 km. Compared to deeper layers of Earth, lithospheric plates are colder, more rigid, and much more brittle (capable of breaking when large forces are applied). The mantle below the plates is called “asthenosphere” or “asthenospheric mantle”. This part of the mantle is not liquid but it is close to its melting temperature. It is therefore capable of flowing (at very slow rates) if forces are applied for long times. Silly putty is a useful analog to the mechanical behavior of the asthenosphere.
Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication.
You can find this at .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes;
AKA: Lithospheric plate
The ~100-km-thick surface of the Earth;
Contains crust and part of the upper mantle;
It is rigid and brittle;
Fractures to produce earthquakes.

23. World Plates This diagram shows the major Tectonic Plates.
Presenter: Point out the UK, sitting on the Eurasian Plate. Also the plate boundary between Africa and South America (note that it has the same shape as the coastlines in these countries).

24. What are tectonic plates made of?
Plates are made of rigid lithosphere.
The lithosphere is made up of the crust and the upper part of the mantle.
Plates are made of rigid lithosphere – formed of the crust and the extreme upper mantle (point out these layers on the figure).

25. What lies beneath the tectonic plates?
Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.
The asthenosphere, beneath the lithosphere, is part of the upper mantle and is so hot that it is 1 – 5% liquid (I.e. 95 – 99% solid). This liquid, usually at the junctions of the crystals, allow it to flow – which is why ‘astheno’ means weak.’ Beneath the asthenosphere is the rest of the mantle, which is completely solid – but can also flow (on geological time scales) because of the intense temperatures and pressures involved.
The base of the lithosphere-asthenosphere boundary corresponds approximately to the depth of the melting temperature in the mantle.

26. Plate Movement
“Plates” of lithosphere are moved around by the underlying hot mantle convection cells
How and Why do tectonic Plates move around?
The question of how tectonic plates are moved around the globe is answered by understanding mantle convection cells.
In the mantle hot material rises towards the lithosphere (like hot air rising out of an open oven - ever opened an oven door and felt the blast of hot air coming past your face?). The hot material reaches the base of the lithosphere where it cools and sinks back down through the mantle. The cool material is replaced by more hot material, and so on forming a large “convection cell” (as pictured in the diagram).
This slow but incessant movement in the mantle causes the rigid tectonic plates to move (float) around the earth surface (at an equally slow rate).

27. What causes continental drift and plate tectonics?
Copyright © 2010 Ryan P. Murphy

28. Answer! Convection currents (Remember heat rises) move the plates
Copyright © 2010 Ryan P. Murphy