1. announcement Friday 27th: 4th exam; review Weds. 25th, 5.15 PM, here Read from p. 322 (where you left off) through sec. 11.4 -- minimizing the hazard -- can we really bypass extinction due to an impact?

2. Today/Wednesday Meteor impacts: what where how often Extinctions –are they really closely related? –did a meteor impact really kill the dinosaurs? –if not, what did?! Please turn on your clicker

3. Please click true or false: if a meteor is big enough to cause damage it will leave an impact scar 1.T 2.F

4. Most meteors come from 1.Comets from outside the Solar System 2.The asteroid belt 3.Mars 4.A planet that once existed between Jupiter and Saturn

5. Which was is this comet traveling? 1.towards the sun 2.away from the sun 3.could be either towards or away

6. Why are meteorites usually very smooth? 1.They are usually reworked in rivers before they are found 2.Most are found in Antarctica, where the ice works them 3.They are melted by the atmosphere

7. Which part of the moon has more impact scars? 1.Basalt flood plains 2.Granitic highlands 3.Both areas have about equal amounts of impact scars

8. What do impact scars on the moon tell you about the timing of impacts in the solar system? 1.Most of the impacts have occurred in the last 3 billion years 2.The timing of impacts has stayed more-or-less constant over time 3.Most of the impacts occurred more than 3 billion years ago

9. Some terms The vast majority of impacts occurred >3 b.y. ago -- we’re just seeing the remnants Meteor Meteorite –meteorite –asteroid Kinds of meteorites –stony –iron Magnitude/frequency…

10. One more clicker Q (ok, 2)

11. On Friday if I ask you which disasters are the best for discussing magnitude/ frequency, what will you say? 1.Earthquakes & volcanoes 2.Volcanoes & severe weather systems 3.Severe storms & meteors 4.Meteors & earthquakes

12. Why? Earthquakes and volcanoes are nearly always moderate in size and in severity Volcanic eruptions are usually big and not too common, and severe systems happen all the time Severe storms and meteors are common occurrences every day Meteors and earthquakes happen at small scales every day

13. Other concept things Our protection system Speed of impact

14. Remember these things: You have a greater chance of being killed by a meteor than winning the jackpot in the lottery The Earth is “a small target in the cosmic shooting gallery” (P Abbott)

15. Meteor craters Simple vs complex: the ground becomes jello, but on different scales –Meteor Crater –Yuty Crater (Mars) -- better exposed/ preserved than any large crater on earth…

16. www.gc.maricopa.edu simple http://www.metsoc2006.ethz.ch/bilder/Shatter-BedaHofmann.gif

17. complex http://nssdc.gsfc.nasa.gov/imgcat/hires/vo1_003a07.gif