Announcements

• Don’t forget to take the test! (today, tomorrow, Friday before class)

• Don’t discuss the test with classmates until class on Friday.

• Pick up graded homework.

• First project due in 9 days!

Earth as a Planet

4 October 2006

Course Outline

• Naked-eye astronomy

• Crash course in physics

• Our solar system

• The stars

• Structure and history of the universe

Course Outline

• Naked-eye astronomy

• Crash course in physics

• Our solar system

• The stars

• Structure and history of the universe

You are

here

Today:

• Some important characteristics of Earth to keep in mind as we compare it to other planets

The planets, to scale

Earth

• My favorite planet• Largest known rock• Very geologically active• Atmosphere of nitrogen

and oxygen• 3/4 covered with water• Nice, comfortable surface

temperature• Only known home of life

Earth: Geology

Earth: Geology

Earth: Geology

Earth

• Made of rock (why?)• Hot inside (why?)• Atmosphere of nitrogen

and oxygen (why?)• 3/4 covered with water

(why?)• Nice, comfortable surface

temperature (why?)

Some partial answers• Made of rock because heavy atoms (Si, O, C, Ca, Na,

K, Fe, Mg) tend to form rocks, and light atoms (esp. H, He) are uncommon on earth (why?)

• Hot inside because of radioactive decay of rare atoms (U, Th, K, Rb), plus some residual heat from earth’s formation; heat builds up and escapes slowly due to earth’s size

• Atmosphere of nitrogen (N2) and oxygen (O2) because plant life has removed most carbon dioxide (CO2) and produced oxygen

• 3/4 covered with water because of size and surface temperature

• Nice, comfortable surface temperature because of our distance from the sun

Earth: Life

Earth’s Moon

• 1/4 earth’s diameter• 1/80 earth’s mass• Covered with craters,

ancient lava flows • Geologically inactive• No atmosphere• Essentially no water• Hot days, cold nights• Only other world humans

have visited