2.  Formation of Universe: 13-20 billion years  Big Bang Theory  Formation of Galaxy: 11 billion Years  Formation of Solar System: 4.6 billion years  Probably takes 10-100 million years for planets to form

5.  Planets made of same material as Sun, minus elements that remain mostly in gases  Inner Rocky Planets: iron and magnesium silicates  Outer gas giants and moons: water ice  If a protoplanet gets big enough, it can hold everything (Jupiter, Saturn)  Very far from sun: methane, ammonia, nitrogen ice

6.  Over 970 (973 as of 9/14/13) extrasolar planets known  262 may be habitable planets  Most known are Jupiter-size planets, larger and easier seen  Super-Earths actually outnumber giant planets

8.  Planets formed by accretion of smaller objects = impact  Very tiny objects hold together by atomic forces  Objects kilometers across hold together by gravity  How do objects the size of a refrigerator hold together?  As planets get bigger, gravity gets stronger, impacts get more violent  Big impacts throw out ejecta, trap heat  Magma ocean  Formation of core early in earth history as iron sinks

10.  It's very hard to account for the Moon:  Very big compared to its parent planet  Orbits nearly in plane of earth's orbit, not over equator.  Co-creation with Earth?  Fission?  Capture?

11.  Over 4 billion years ago  Can explain why moon orbits in earth's orbital plane  Can explain why moon's composition differs from earth  Models of solar system evolution suggest that last stage is mega-collisions  Impact would have melted most of earth and moon  Earth would have been incandescent for about 10,000 years

13.  May have been several moon-forming events  1000-km impactors can melt crust  100-km impactors create temporary atmosphere of vaporized rock, vaporize oceans  Life not possible until large impacts cease  To have life on Earth, we need Jupiter?  Sweeps up debris and reduces impacts  Stabilizes orbits of other planets  To have life on Earth, we need Moon?  Stabilizes changes in earth's axis tilt

15.  Oldest existing earth materials: 4.1 billion years old  Oldest rocks: 3.9 billion years old  Oxygen-poor atmosphere (present oxygen is created by life)  Faint Early Sun: perhaps 30% less bright  Evidence for liquid water from very early on

16.  Earth the Biography: Origin of the Oceans Earth the Biography: Origin of the Oceans

17.  Oxygen levels in atmosphere  Plants release waste oxygen  Eventually organisms developed a way to utilize oxygen  Sex: Who Needs It?  We are a team: Mitochondria  Snowball Earth: what survived and how?  Cambrian "Explosion"

21.  Climate Change  Disease  Mountain-building  Sea Level Change  Competing Organisms  Over-specialization  Volcanism  Meteor Impact  Humans

22.  The Early Earth and Plate Tectonics The Early Earth and Plate Tectonics