Why does the Earth have volcanoes?

Why is there Earthquakes?

How and when did the Earth form?

Turn to your neighbor and review:

How old are the first traces of life on Earth?

Logical?

*

1.5Ga (1st multicellular life)

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

1st Ocean Formation ~4.4GaVolcanic 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.

Stromatolites date back over 3Ga.

cyanobacteria use photosynthesis.

Hard times for

anaerobic organisms

O2

New atmosphere composition�big changes

for organisms.

*

PHOTOSYNTHESIS3.5 Billion Years Ago*

Stromatolites: in the fossil record 3.5 billion years ago

and can still be found at Sharks Bay.

What are the compositional and mechanical

layers of the Earth and how did they form?

* Turn to your neighbor and review:

Mechanical vs. Compositional layers

You should be thinking—

How do we know this?

(mostly iron and some nickel)

(rock)

*

Key Terms:

Oceanic Crust

Continental Crust

Lithosphere

Mantle

Outer Core

Inner Core

*

MOHO

*

Through what process

did the layers of the

Earth form?

GraniteContinental Crust

Usually around 30km but up to 70km thick.

BasaltOceanic Crust

Thin: usually 7-10km

Density 2.7g/cm3 Density 3.0g/cm3

Which would be more buoyant?

*

MOHO

Layers Thickness Composition State/Density

Oceanic crust

3-10 km Si, O, Fe, Mg, Al

= Basalt

2.9 g/cc SOLID

Continental crust

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

RIGID, SOLID, BRITTLE: breaks into plates

Asthenosphere 100-350 km Portion of mantle

Plastic (flows), but SOLID

Individually (without book):

Draw a picture of Earth’s layers (make it a full Earth circle) – include:

AsthenosphereCore (Inner + Outer)

CrustLithosphere

MantleMoho

In groups of 4-5 – introduce self:

Review each other’s pictures of Earth’s layers. Give feedback. Include:

AsthenosphereCore (Inner + Outer)

CrustLithosphere

MantleMoho

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?

*

Residual heat from

asteroid accretion.

Radioactive decay

The Earth’s internal heat comes from:*

Lord Kelvin

(1824-1907)

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.

12 major plates and many smaller (micro) plates

Earth processes need energy to work—

what provides the energy?

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.

Earth’s internal heat engine.*

A consequence of convection:

Plate TectonicsSpreading Center

Convection in the

mantle (which is solid

but it flows).

*

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’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.

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?

438 Million Years AgoLIFE LEAVES OCEAN AND MOVES ONTO

LAND

*

12 major plates and many smaller (micro) plates

*

Rock Cycle

Igneous Rocks

Form from melts.

Sedimentary

Rocks

Form from

sediments

Metamorphic Rocks

Form from any pre-existing

rock that changed due to

Increased heat or pressure.

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)

AfricaSouth America Mid-Atlantic Ridge

*

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.

• Quiz each other on the types of plate

boundaries.

• Name the types.

• What are the plate motions and stress

types?

• What are some locations?

Turn to your neighbor and review:

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

Seismic Tomography

Mantle Plume

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

Crust thickness in kilometers

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

Paleomagnetic Studies

Seafloor Age from magnetic studies,

and drilling and sampling.

Pillow Basalt forms at mid-

ocean ridges

Pillow Basalt

Seafloor Magnetic Anomalies

Figure 2.16

Figure 2.14

We can see things moving!

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.

Transform

Plate

Boundaries

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!