Lecture 14: The Earth

"I am a passenger on the spaceship Earth."
R. Buckminster Fuller

Navigation Options

You may :

Go to the Astro 105 Main Menu

Go to the Class Schedule

Look at the Review Questions for Lecture # 14

Go to the Lecture # 13 Master Page

Go to the Lecture # 15 Master Page

Date: October 25, 1994
Reading Assignment: pp. 152-168

Description : Geology of Earth, radioactive dating, plate tectonics.

Objectives

understand radioactive dating techniques

understand how we can map the center of the Earth using Earthquakes

understand how plate tectonics lead to geological features

be able to list processes of erosion

Lecture Outline

Slide # 1: Lecture 14: The EarthÕs Interior

Click here for subtitle

atmospheric review

the EarthÕs core

radioactive dating

plate tectonics

erosion

Slide # 2: Lecture 13: The Earth and its Atmosphere

hydrosphere and tides

atmosphere

ozone layer and greenhouse effect

magnetosphere

Slide # 3: EarthÕs Structure

core

mantle

crust

hydrosphere

atmosphere

magnetosphere

Slide # 4: Ozone

most X-rays and UV are blocked by the Ozone layer

X-rays and UV are bad for life on Earth

Slide # 5: Destruction of the Ozone Layer

freon and chlorofluorocarbons destroy Ozone

one freon molecule destroys millons of Ozone molecules

Slide # 6: The Runaway Greenhouse Effect

carbon dioxide blocks infrared light

the amount of carbon dioxide in the atmosphere is increases 4% per decade

burning fossil fuels

destruction of the oceans

global temperatures are slowly rising

the global climate is being altered by MAN

Slide # 7: The Runaway Greenhouse Effect

most of the carbon dioxide on Earth is contained in rocks

heating the rocks causes the release of the carbon dioxide

Slide # 8: The Runway Greenhouse Effect

the cycle of doom

Slide # 9: Origin of the Atmosphere

primary atmosphere- Hydrogen and Helium

gases common in the solar system

escaped from Earth

secondary atmosphere

volcanic outgassing

Nitrogen, CO2, sulfur dioxide, wator vapor, methane

most of these gases are trapped in rocks now

Slide # 10: The Current Atmosphere

early plant life changed some of the CO2 into O2

most of the CO2 is trapped in rocks

ozone layer formed from the oxygen

Slide # 11: Why is the sky blue?

dust particles scatter more blue light than red

Slide # 12: Sunset

red light passed through atmosphere

most blue light is scattered

Slide # 13: The Magnetosphere

the EarthÕs Magnetic Field

Slide # 14: The Magnetosphere

high energy particles are trapped by the magnetic field

radiation zones form

the Van Allen belts

Slide # 15: Aurora

the magnetic field traps particles from the ÒSolar WindÓ

the particles strike atmosphere near the Poles

Northern and Southern lights result

Slide # 16: Magnetosphere

also protects Earth from high energy particles

Slide # 17: Formation of the Magnetic Field

the magnetic field of Earth changes polarity about every 700,000 years

the magnetic field is caused by convection inside the EarthÕs core

Slide # 18: Convection

heating a gas (or liquid) causes it to expand

expanded gases have a lower density

lower density objects ÒfloatÓ

Slide # 19: Convection

hot liquids rise, cool liquids sink

Slide # 20: Convection is important

inside the EarthÕs core

forms magnetic fields

in the EarthÕs atmosphere

weather and turbulence

Slide # 21: Probing EarthÕs Interior

we canÕt directly observe the EarthÕs core

we can probe using Seismic Waves

Slide # 22: Two Types Seismic Waves

P-waves

pressure waves

S-waves

shear waves

Slide # 23: P-waves

pressure waves

Slide # 24: S-waves

shear waves

Slide # 25: P and S waves

S waves cannot travel through liquids

P waves can travel through liquids and solids

Slide # 26: Earthquakes as Experiments

Earthquakes can be detected around the Earth

seismic signals pass through the Earth

we use these signal to probe the interior

Slide # 27: Earthquake Experiments

detectors placed around the Earth

Slide # 28: Earthquake Experiments

Experimental Results

Slide # 29: Earthquake Experiments

the path of seismic waves

Slide # 30: Earth has a liquid interior

P waves pass directly through

S waves are blocked by the liquid

P waves are refracted at the core boundary

Slide # 31: Internal Structure of Earth

Mantle, outer and inner core

Slide # 32: Models of the Interior

crust- rocky elements

silicon-aluminum

mantle- rocky elements

iron-magnesium-silicates

core - metallic elements

iron-nickel

Slide # 33: Differentiation

in a liquid

heavy things sink

light things float

in the liquid interior of a planet

light rocks rise to the surface

heavy rocks sink to the core

Slide # 34: The Liquid Earth

Earth must have been liquid

Energy to keep Earth molten

Debris hitting Earth during formation

Radioactive heating

Slide # 35: Radioactive Dating

some elements spontaneous change into other elements

the nuclei change

Slide # 36: Half-life

the time for half of a sample to decay

a statement of probability

we donÕt know WHICH atoms will change

each atom has a 1 in 2 chance to decay in one half-life

since most samples contain trillions of atoms, the statistics are very good

Slide # 37: Parent and Daughter Atoms

Parent atoms are the original sample

Daughter atoms are the results of the decay

Slide # 38: Some half-lives

U238 = 4.5 Billion Years

U235 = 713 Million Years

Thorium-232 = 13.9 Billion Years

Plutonium-241 = 2.4 Million Years

Carbon-14 = 6000 years

Slide # 39: Many Half-Lives

every half life will decrease the amount of PARENT atoms by 1/2

Slide # 40: How do we know the sample started as only Parent Atoms?

if the Daughter atoms are gaseous, they would not stay in the rock if it was M

radioactive decay measure when the rock was last a liquid

Slide # 41: Daughter Atoms

many radioactive substances produce Helium as a daughter atom

Helium does not chemical combine with other elements.

Helium escapes from EarthÕs atmosphere.

ALL the Helium found inside the Earth was formed from radioactive decay.

Slide # 42: Radioactive Dating: the Results

oldest rocks on Earth are 4 billion years old

most meteors are 4.6 billion years old

none are older

oldest Moon rocks are 4.6 billion years old

Slide # 43: Surface Features on Earth

Earth is geologically alive

the surface is ÒyoungÓ and changing

Slide # 44: Plate Tectonics

active geological sites are only found on well-defined lines

these lines are the edge of geological plates

Slide # 45: Plates in Motion

continental drift fits geological and fossil record

observed DIRECTLY by astronomical telescopes

paleomagnetism

Slide # 46: A Cross Sectional View

crust, lithosphere, aethenosphere

Slide # 47: Why are they called Plates?

50km thick

1200km wide

similar proportions to dishware

Slide # 48: Direct Collisions Between Plates

mountain building

Slide # 49: Direct Collsions Between Plates

subduction zones (ocean trenches)

Slide # 50: Earthquakes

caused by sudden, jerky motion between two plates

Slide # 51: Erosion

wearing away of surface features

caused by

water

wind

ice

Slide # 52: A Quick Review Slide # 53: Light and EM energy

waves

wave- and particle-like nature of light

EM spectrum

the atmosphere

thermal radiation

Doppler Effect

Slide # 54: Line Emission

Spectral Lines

KirchoffÕs laws

Bohr atom

Line Broadening

Slide # 55: Optical Telescopes

reflectors/refractors

LGP/resolution/magnfication

CCD/photography/the eye

coma/chromatic aberration

seeing/resolution

Slide # 56: None-Optical Telescopes

interferometry

atmospheric effects

Slide # 57: EarthÕs Structure

core

mantle

crust

hydrosphere

atmosphere

magnetosphere