The rest of the semester

1. Today and next week: Meteor impacts and extinctions

2. Friday 27th: 4th exam, review Weds. 25th, 5 PM, here

3. M/W/F April 30/May 1/May 3: final group project on coastal hazards

4. W May 9, 10 - 12, final exam. Go to http://home.nau.edu/registrar/final_exam_1071.asp for university policy on final exams (including how many you have to take in one day)

Today/M/W

• 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

The next slide has a few options for how sediment is moved along

a shoreline by longshore drift. Which one is accurate?

A

B

C

Current direction for all options

Why does drift move in that pattern?

1. The current along the shore is moving that way, so the sand follows the current

2. Water flows downhill from shore, no matter how it’s brought in to shore

3. Sand moves in opposition to the current along the shore

What is the most obvious change in waves as they come to shore

1. They slow down

2. The wave height decreases

3. The wavelength (crest to crest) decreases

What is the general relation between

wave height and wave energy? 1. The higher the wave, the more energy

it has

2. The higher the wave, the less energy it has

3. Wave energy is derived from the steepness of the beach, not the height of the wave

What’s wrong with this picture?

longshore current

1. Nothing -- makes sense

2. Sand should pile up on the right side of the groins

3. Sand should pile up on the left side of the groins

4. The area along the shore behind the groins should be eroded

Okay, on to meteors

• Read (you knew this was coming) – p. 314 - 322 (to the paragraph that starts with

“Geologically, ancient impact craters…”)

1. Meteors and their impacts

What are they? How common are they?

• Cosmic debris of any sort

• Where do they come from?

• A short exercise to figure out how common they are and why

www.wcnet.org/~kmkerr/ Solar_system/Comets.htm

www.gc.maricopa.edu

Some pictures…

www.gc.maricopa.edu/earthsci/imagearchive/meteorcrtr.jpg

Why are they so smooth?

With your group, please (>1 person, <5 people)…

• Your names, and then answers:

PART I

1. What does plate tectonics do to the earth’s crust?

2. Are there a lot of impact scars on earth?

3. What is the relation between plate tectonics and the presence/absence of impact scars?

PART II

• Use the images on the screen and the little assignment slips of paper and write the paragraph requested:

If you can assume that all bodies/planets/moons in the solar system

have been treated alike, is there some time in the past that most meteor bombardment

occurred, or has the rate remained constant over time?

The three pictures are all of our moon