the essential cosmic perspectiven00006757/astronomylectures... · leads to ice ages (every 10,000...
TRANSCRIPT
The Essential Cosmic PerspectiveChapter 7.5: Earth as Living Planet
Dr. Regina Jorgenson
WARNING:14,000 feet feels
different!
Outline
• What unique features of Earth are important for life?
• How is human activity changing our planet?
• What makes a planet habitable?
What unique features of Earth are important for life?
(compare & contrast with Venus and Mars)
1) Surface liquid water
Venus & Mars:NO surface liquid water
T = 461C
T = -50C
2) Atmospheric Oxygen
Question: Suppose that all photosynthetic 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 ago
Question: If the motions of one plate relative to another is 1 cm per year, how long would it take
for 2 continents 3000 km apart to collide?
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 relative to another is 1 cm per year, how long would it take
for 2 continents 3000 km apart to collide?
1) 30,000 years
2) 3,000,000 years
3) 300,000,000 years
4) 3,000,000,000 years
How many cm in 3,000 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 to mantle
Crust creation and recycling!
America and Europe are
moving apart by 3cm per year =
30 km per million years.
This continental drift is measured
by GPS.
Earth: Cold rigid crust that
breaks up
Venus: Hot plastic crust that does not breaks up
No plate tectonics on Venus
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 Sun conditions -- the Sun has brightened 30% over the past 4 billion years -- how was the Earth 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 Sun conditions -- the Sun has brightened 30% over the past 4 billion years -- how was the Earth 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 thermostat
Rate dependent on temperature
Temperature increases
more evaporation/
rainfall
less CO2 in atmosphere
less greenhouse
effect
Temperature decreases
Temperature decreases
less evaporation/
rainfall
more CO2 in atmosphere
more greenhouse
effect
Temperature increases
Question: Let’s recap! Which four unique features of Earth are important
to life?
1) surface liquid water, oil, atmospheric Oxygen and 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 four unique features of Earth are important
to life?
1) surface liquid water, oil, atmospheric Oxygen and 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 activity changing our planet?
There are historical climate changes that occur “naturally” due to things like small cyclical changes in Earth’s axis tilt or major volcanic releases of CO2.
leads to ice ages (every 10,000 years or so)
Global Warming
Global average temperature increased 0.8 C in past century
What is causing global warming?
The Greenhouse Effect
greenhouse gases are:
methane
CO2
water vapor
The Greenhouse Effect
greenhouse gases are:
methane
CO2
water vapor
Note! Greenhouse Effect is crucial for life! But too
much of a good thing can be bad... i.e. Venus
Proof? We see the greenhouse effect on other planets
CO2 levels today are higher than at any 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 scientist tasked
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 what this graph is showing?
Discussion Questions
What could be causing the increase in CO2 levels over
the past 50 years?
Discussion Questions
Bonus points: Can you explain 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 century simply from heating of water
FLOODING:
What makes a planet habitable?
Size Matters: Which cools faster?
12
3
Planetary Size
Small
Large
relative sizes
Mercury Venus Earth Mars
Transit of Venus: June 5, 2012
Distance from Sun
Hot core enabled magnetic field
Magnetic field protects Earth from harmful solar particles and creates
aurora borealis
Now you are a scientist tasked with locating other Earth-like
planets where human life could possibly exist.
How would you do this?
Search for extra-solar planets
Kepler Space Telescope
CO2 levels correlate with temperature