Why does the Earth have volcanoes? Why is there Earthquakes?

Why does the Earth have volcanoes? Why is there Earthquakes?

Turn to your neighbor and review: How and when did the Earth form? How old are the first traces of life on Earth? Logical?

* 1.5Ga (1 st multicellular life)

Just right for liquid water --water is plentiful in all 3 phases on Earth--

* 1 st Ocean Formation ~4.4Ga Volcanic out-gassing and comets

earliest life forms found

Moon (Earth s) ~No atmosphere No Liquid water No plate tectonics = no erosion ---but impacts continue to occur and there is cosmogenic bombardment.

* LIFE EVOLVES 3.8 Billion Years Ago

* Oxygenation of Earth s atmosphere (also known as the Oxygen Catastrophe) The appearance of free oxygen (O2) in Earth's atmosphere 2.4 billion years ago. O2 Hard times for anaerobic organisms New atmosphere composition big changes for organisms. Stromatolites date back over 3Ga. cyanobacteria use photosynthesis.

Stromatolites: in the fossil record 3.5 billion years ago and can still be found at Sharks Bay. * PHOTOSYNTHESIS 3.5 Billion Years Ago

* Turn to your neighbor and review: What are the compositional and mechanical layers of the Earth and how did they form?

* Mechanical vs. Compositional layers (rock) (mostly iron and some nickel) You should be thinking How do we know this?

* Key Terms: Oceanic Crust Continental Crust Lithosphere Mantle Outer Core Inner Core

* MOHO Through what process did the layers of the Earth form?

Granite Continental Crust Usually around 30km but up to 70km thick. Basalt Oceanic Crust Thin: usually 7-10km * Density 2.7g/cm 3 Density 3.0g/cm 3 Which would be more buoyant?

MOHO

Layers Thickness Composition State/Density Oceanic crust Continental crust 3-10 km Si, O, Fe, Mg, Al = Basalt 2.9 g/cc SOLID 30-50 km Si, O, Al = Granite 2.7 g/cc SOLID Mantle 2900 km Mg, Fe, Si, O 4.5 g/cc SOLID Outer core 2200 km Fe, Ni (S, Si) 11 g/cc LIQUID Inner core 1300 km Fe, Ni (S, Si) 16 g/cc SOLID Overlaid layers: Lithosphere 100-200 km 100% Crust + Upper Mantle Asthenosphere 100-350 km Portion of mantle RIGID, SOLID, BRITTLE: breaks into plates Plastic (flows), but SOLID

Individually (without book): Draw a picture of Earth s layers (make it a full Earth circle) include: Asthenosphere Core (Inner + Outer) Crust Lithosphere Mantle Moho

In groups of 4-5 introduce self: Review each other s pictures of Earth s layers. Give feedback. Include: Asthenosphere Core (Inner + Outer) Crust Lithosphere Mantle Moho

What are the two types of crust? What are their thicknesses? What are their densities? What are their compositions? What are their relative ages?

What are the two types of crust? Oceanic and Continental What are their thicknesses? Oceanic avg~7km, Continental 30-50km What are their densities? Oceanic ~3g/cm^3, Continental ~2.7g/cm^3 What are their compositions? Oceanic is Basalt (mafic), Continental is Granite (felsic) What are their relative ages? Oceanic 0-200Ma, Continental 0-4Ga

* The Earth is slowly cooling but where does all that internal heat come from?

* The Earth s internal heat comes from: Residual heat from asteroid accretion. Radioactive decay

In the late 1800 s Lord Kelvin calculated the age of the Earth to be 100 million years old using thermal gradient. He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface to cool to its present temperature. His calculations did not account for heat produced from radioactive decay (which was unknown at the time) and convection inside the Earth, which allows more heat to escape from the interior to warm rocks near the surface. Lord Kelvin (1824-1907)

12 major plates and many smaller (micro) plates

Earth processes need energy to work what provides the energy?

* Earth s internal heat engine. Convection: Fluid motion due to density difference created by thermal expansion. Warm object expand and becomes less dense, thus buoyant. Warm stuff rises/cool stuff sinks.

A consequence of convection: Plate Tectonics * Convection in the mantle (which is solid but it flows). Spreading Center

Convection

* Convection in the liquid Fe and Ni (iron and nickel) Outer Core: Generates a magnetic field. Yes the Earth is a big magnet. The geomagnetic field is important to life on Earth. It is also a valuable tool for science and navigation.

The Earth has a magnetic field due to convection of the outer core. The magnetic field is thought to have developed about 3.5 Ga. Hmmm-where have I seen that number before? The Earth s magnetic field protects use from solar radiation and it also protects the atmosphere from being stripped away by the solar wind. This magnetic field along with ozone provides a protective shield and allowed life to evolve on land.

* 438 Million Years Ago LIFE LEAVES OCEAN AND MOVES ONTO LAND

12 major plates and many smaller (micro) plates

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Rock Cycle Igneous Rocks Form from melts. Metamorphic Rocks Form from any pre-existing rock that changed due to Increased heat or pressure. Sedimentary Rocks Form from sediments

A craton is a very old, stable continental interiors. Often crystalline metamorphic rock. Cratons are composed of shields and platforms. A platform is sedimentary deposits covering the crystalline basement rocks of a shield.

* Mid-Ocean Ridges (spreading centers, divergent plate boundaries) Large, continuous mountain ranges in ocean basins. These create the oceanic crust.

* Divergent Plate Boundary (most often a MOR) South America Mid-Atlantic Ridge Africa Practice drawing and labeling this picture---you need to know this by memory!

Practice drawing and labeling this picture---you need to know this by memory!

Transform Faults

* Practice drawing and labeling this picture---you need to know this by memory!

* Practice drawing and labeling this picture---you need to know this by memory!

Motion at Plate Boundaries

Practice drawing and labeling this picture---you need to know this by memory! *

Convergent Margins: India-Asia Collision I

Looks like something catastrophic occurred.

Turn to your neighbor and review: Quiz each other on the types of plate boundaries. Name the types. What are the plate motions and stress types? What are some locations?

Plate Tectonics The Supporting Evidence

What we now know and how we know it.

Puzzle fit of the continents

Fossil Evidence

Correlation of Stratigraphic Sequences

Similar Rocks

Mountain Chain Evidence

Hotspot Tracks

Mantle Plume Seismic Tomography

Plate moves over stationary plume.

Emperor Seamounts

Global Hot spot Tracks

For the most part, earthquakes occur along plate boundaries.

Earthquake depth and location

Wadati-Benioff zone

From earthquakes we can see the thickness of the crust---coming up! Crust thickness in kilometers

Paleomagnetic Studies

Seafloor Age from magnetic studies, and drilling and sampling.

Pillow Basalt forms at midocean ridges

Pillow Basalt

Seafloor Magnetic Anomalies

Figure 2.16

Figure 2.14

We can see things moving!

Transform Plate Boundaries The San Andreas Fault is a right lateral strike-slip fault. If you stand facing it everything on the other side of the fault is moving to the right relative to you at an average rate of about 3-4 cm/yr. Some places along the fault are continually creeping along very slowly. Other places are locked up. These locked up zones break free and move occasionally. We feel this as earthquakes.

Satellites can detect and measure motion of the ground!

Satellites and ground based observations are measuring plate movements. We know the rate and direction of movement of many locations.

Global Positioning Satellites (GPS) and Very Long Baseline Interferometry (VBLI) Have confirmed that plates do move! Have measured the rates of movement! Plate Motion Rates in cm/yr

1964 Alaska earthquake fault scarp. Wowza!