Announcements Dont forget to take the test today

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 You are here The stars Structure and history of the universe

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 (N 2) and oxygen (O 2) because plant life has removed most carbon dioxide (CO 2) 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