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