The Essential Cosmic PerspectiveChapter 7.5: Earth as Living Planet

Dr. Regina Jorgenson

WARNING:14,000 feet feels

different!

To see original MOV file, click here

Outline• What unique features of Earth are

important for life?

• How is human activity changing ourplanet?

• What makes a planet habitable?

What unique features of Earthare important for life?

(compare & contrast with Venus and Mars)

1) Surface liquid water

Venus & Mars:NO surface liquid water

T = 461CT = -50C

2) Atmospheric Oxygen

Question: Suppose that allphotosynthetic life (i.e. plants) died out.What would happen to all the oxygen in

our atmosphere?Could animals, including us, survive?

3) Plate Tectonics

>12 plates, moving at ~few cm per year (fingernail speed)

millions of years agoTo see original MOV file, click here

Question: If the motions of one plate relativeto another is 1 cm per year, how long would it

take for 2 continents 3000 km apart tocollide?

• 1) 30,000 years

• 2) 3,000,000 years

• 3) 300,000,000 years

• 4) 3,000,000,000 years

Question: If the motions of one plate relativeto another is 1 cm per year, how long would it

take for 2 continents 3000 km apart tocollide?

• 1) 30,000 years

• 2) 3,000,000 years

• 3) 300,000,000 years

• 4) 3,000,000,000 years

How many cm in3,000 km?

1 km = 105cm =100,000 cm

3,000 km = 3,000 x 105 cm = 3 x 108 cm = 300,000,000 cm

Subduction: plate material returning tomantle

Crust creation and recycling!

America andEurope are

moving apartby 3cm per

year = 30 kmper million

years. Thiscontinental driftis measured by

GPS.

Earth:Cold rigid crust that

breaks up

Venus:Hot plastic crust thatdoes not breaks up

No plate tectonics onVenus

4) Climate Stability

Venus: Too hot!(runaway greenhouse)

Mars: Too cold!(lost atmosphere)

4) Climate Stability

Earth: Just right! (Goldilocks planet)(runaway greenhouse)

Question: Considering changing Sunconditions -- the Sun has brightened 30%

over the past 4 billion years -- how was theEarth able to maintain long-term climate

stability?

• 1) We got lucky

• 2) The Earth’s orbital radius increased

• 3) The size of the Earth increased

• 4) The carbon dioxide cycle

Question: Considering changing Sunconditions -- the Sun has brightened 30%

over the past 4 billion years -- how was theEarth able to maintain long-term climate

stability?

• 1) We got lucky

• 2) The Earth’s orbital radius increased

• 3) The size of the Earth increased

• 4) The carbon dioxide cycle

Carbon Dioxide Cycle (CO2

Cycle)a.k.a. Earth’s long-term thermostat

Carbon Dioxide Cycle (CO2

Cycle)a.k.a. Earth’s long-term thermostatRate dependent on temperature

Temperatureincreases

moreevaporation/ra

infall

less CO2 inatmosphere

lessgreenhouse

effect

Temperaturedecreases

Temperaturedecreases

lessevaporation/ra

infall

more CO2 inatmosphere

moregreenhouse

effect

Temperatureincreases

Question: Let’s recap! Which fourunique features of Earth are

important to life?

• 1) surface liquid water, oil, atmospheric Oxygenand CO2, plate tectonics

• 2) surface liquid water, Oxygen, CO2, dinosaurs

• 3) surface liquid water, atmospheric Oxygen,plate tectonics, climate stability

• 4) pizza, the internet, iphones, beer

Question: Let’s recap! Which fourunique features of Earth are

important to life?

• 1) surface liquid water, oil, atmospheric Oxygenand CO2, plate tectonics

• 2) surface liquid water, Oxygen, CO2, dinosaurs

• 3) surface liquid water, atmospheric Oxygen,plate tectonics, climate stability

• 4) pizza, the internet, iphones, beer

How is human activitychanging our planet?

• There are historicalclimate changes thatoccur “naturally” dueto things like smallcyclical changes inEarth’s axis tilt ormajor volcanicreleases of CO2.

•leads to ice ages(every 10,000 yearsor so)

Global Warming

Global average temperature increased 0.8 C in pastcentury

What is causing globalwarming?

The Greenhouse Effect

greenhouse gases

are:

methaneCO2

water vapor

The Greenhouse Effect

greenhouse gases

are:

methaneCO2

water vapor

Note! Greenhouse Effectis crucial for life! But toomuch of a good thing can

be bad... i.e. Venus

Proof? We see thegreenhouse effect on other

planets

CO2 levels today are higher than atany point in the past 400,000 years

Temperature variation

CO2

Thousands of years ago

Temperature variation

CO2

Thousands of years ago

Question:What do you see when you compare these graphs?

Temperature variation

CO2

Thousands of years ago

Answer:Periods of higher CO2 concentration correspond

with periods of higher global average temperature

Discussion Question:Imagine you are a scientisttasked with determining the

Earth’s temperature and CO2

levels 400,000 years ago.How would you do this?

Ice Cores!

Similar to tree rings,ice layers are a

record of the past

CO2 levels correlate with temperature

Discussion Questions

Discussion Questions

Can you explain whatthis graph is showing?

Discussion Questions

What could be causing theincrease in CO2 levels over

the past 50 years?

Discussion Questions

Bonus points: Can youexplain the detailed

behavior of the data?(i.e. the red line)?

Alps, January 2004 Alps, June 2004

Effects of Global Warming?

Melting polar ice caps & Melting ice sheets

Greenlandwhite = year round ice sheet

orange = melt region

sea level rise of 1 metercould occur within the centurysimply from heating of water

FLOODING:

What makes a planethabitable?

Size Matters: Which coolsfaster?

12

3

PlanetarySize

Small

Large

relative sizes

Mercury Venus Earth Mars

Transit of Venus: June 5, 2012

Distance from Sun

Hot core enabled magneticfield

Magnetic field protects Earth fromharmful solar particles and creates

aurora borealis

To see original MOV file, click here

Now you are a scientist taskedwith locating other Earth-like

planets where human lifecould possibly exist.

How would you do this?

Search for extra-solar planets

Kepler Space Telescope

CO2 levels correlate with temperature