7.5 Earth as a Living Planet
• Our Goals for Learning
• What unique features on Earth are important for human life?
• How might human activity change our planet?
• What makes a planet habitable?
What unique features of Earth are important for life?
1)
2)
3)
4)
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
What unique features of Earth are important to human life?
1)
2)
3)
4)
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
Earth’s distance from the
Sun and moderate
greenhouse effect make
liquid water possible
What unique features of Earth are important to human life?
1)
2)
3)
4)
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
PHOTOSYNTHESIS
(plant life) is required to
make high concentrations
of O2, which produces the
protective layer of O3.
What unique features of Earth are important to human life?
1)
2)
3)
4)
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
Plate tectonics are
an important step
in the carbon
dioxide cycle.
The Carbon Dioxide Cycle
What unique features of Earth are important to human life?
1)
2)
3)
4)
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
The CO2 cycle acts like a
thermostat for the Earth’s
temperature.
These unique features are intertwined:
• plate tectonics creates climate stability
• climate stability allows liquid water
• liquid water is necessary for life
• life is necessary for atmospheric oxygen
How many other connections between these can you think of?
How might human activity affect Earth’s climate?
Earth’s ice ages end as oceans freeze over and volcanoes release CO2 into the atmosphere Human activity is increasing the concentration of greenhouse gases in the atmosphere, which may strengthen the greenhouse effect and lead to global warming.
What makes a planet habitable?
• Located at an optimal distance from the Sun for liquid water to exist.
What makes a planet habitable?
• Large enough for geological activity to release & retain water and atmosphere.
Planetary Destiny
Earth is habitable because it is large enough to remain geologically active and at the right distance from the Sun so oceans could form.
What have we learned?
• What unique features of Earth are important for life?
• Unique features of Earth on which we depend for survival are
• (1) surface liquid water, made possible by Earth’s moderate temperature;
• (2) atmospheric oxygen, a product of photosynthetic life; • (3) plate tectonics, driven by internal heat; and • (4) climate stability, a result of the carbon dioxide cycle, which in turn requires plate tectonics. What have we learned?
• How might human activity change our planet?
• Ozone depletion can leave surface life more vulnerable to dangerous solar ultraviolet radiation, and the high rate of extinctions could have unknown consequences. The human release of greenhouse gases into the atmosphere is already causing global warming and certainly would affect the climate if it continues. What have we learned?
• What makes a planet habitable?
• We can trace Earth’s habitability to its relatively large size and its distance from the Sun. – Its size keeps the internal heat that allowed volcanic outgassing to lead to our oceans and atmosphere, and also drives the plate tectonics that helps to regulate our climate through the carbon dioxide cycle. – Its distance from the Sun is neither too close nor too far, thereby allowing liquid water to exist on Earth’s surface.