Post on 20-Aug-2018
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