Chapter 7eEarth is a living planet

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) Surface liquid water

2) Atmospheric oxygen

3) Plate tectonics

4) Climate stability

What unique features of Earth are important to human life?

1) Surface liquid water

2) Atmospheric oxygen

3) Plate tectonics

4) 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) Surface liquid water

2) Atmospheric oxygen

3) Plate tectonics

4) Climate stabilityPHOTOSYNTHESIS (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) Surface liquid water

2) Atmospheric oxygen

3) Plate tectonics

4) 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) Surface liquid water

2) Atmospheric oxygen

3) Plate tectonics

4) Climate stability The CO2 cycle acts like a thermostat for the Earth’s temperature. Liquid water (oceans) is also important!

These unique features are intertwined:

• plate tectonics creates climate stability• climate stability allows liquid water• liquid water is necessary for life (afawk)• 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 may already be 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.