1. “Between impulse and action, there is a realm of good taste begging for your acquaintance.”
The Doctor, Star Trek Voyager
Clickers turned on? Phones put away
OAAC meeting Tuesday 6:30pm in Kemper Hall 101.

2. Last time: Seasons.
You guys did great!

3. The reason for Earth's seasons Because the Earth’s spin is tilted by 23.5 degrees!

4. From our location, the Sun is never directly overhead or north of us at noon.

5. The Universe loves pancakes! Our solar system is mostly flat.

6. HYPOTHETICAL What would you ask if I said a new planet has been discovered in our solar system?

7. HYPOTHETICAL What would you ask if I said a new planet has been discovered in our solar system? What information would likely exist?

8. Last Time:
The Earth-Moon System:
Features -vs- Interpretations

9. Features we see and what they tell us.

10. Features we seeand what they tell us.
Some Examples
Round- means it is massively big.
well-defined features: solid
Fuzzy-swirly features: gas: check with multiple images.
Smooth features: liquid
multiple colors- changes in temperature, composition, or altitude.
There are always exceptions.

11. Compare and contrast what features we see on the Moon with those of the Earth.

12. And now for the Moon

14. And now for the Moon

15. In 2 sentences, describe the Earth.
Do the same for the Moon.
Do this as if you’re describing them for an alien unfamiliar with either object.

16. In 2 sentences, describe the Earth. Do the same for the Moon.
ON PAPER: pick 4 of your neighbors and come to a common description.

17. Put your names on this paper and pass it to your right, to the aisle.
This will count as 15pts of homework.

18. Which body is older, the Earth or the Moon?

19. Which body is older, the Earth or the Moon? Quiz 1

20. Which body is older, the Earth or the Moon?
Is there a way to know for sure?

21. Which body is older, the Earth or the Moon?
Is there a way to know for sure?
Yes, radioactive dating (to be discussed)

22. Why is the Moon smothered with craters, but the Earth isn't?

23. Why is the Moon smothered with craters, but the Earth isn't?
Erosion: resurfacing and weathering.

24. Why is the Moon smothered with craters, but the Earth isn't?
Does the Earth have any craters?

25. Craters on Earth

26. What are some types of erosion?

27. What are some types of erosion?
Wind
Rain & water run-off
Oceans & lakes
Vegetation
Plate motions- earthquakes
Volcanoes

29. Back to: How can we determine the age of the Earth? For the surface
We can use radioactive (carbon) dating to tell how old rocks we find are. When rocks solidify, they lock-in the elements they are made of. The ½ life of Carbon 14 (when ½ of the original carbon would have been changed to nitrogen 14) is years. The ½ life of Potassium 40 (which decays to Argon 40) is 1.25 billion years.

30. How old is old?
The oldest rocks found on Earth are about 4 billion years old. Yet the average age of the Earth's surface is about 200 million years old.
4.4 Gyr old mineral
4.28 Gyr old rock outrcopping
3.9 Gyr old rock with chemical traces of life

31. How do they know that the rock is really a billion years old, or did it just have less potassium 40 to begin with?

32. How do they know that the rock is really a billion years old, or did it just have less potassium 40 to begin with?
Evidence 1: Most importantly, do this for many different isotopes to ensure consistent results.

33. How do they know that the rock is really a billion years old, or did it just have less potassium 40 to begin with?
Evidence 2: Compare rocks that you know the ages of: Volcanoes with known eruption dates.

34. How do they know that the rock is really a billion years old, or did it just have less potassium 40 to begin with?
Evidence 3: Compare rock ages with age estimates of geologic features.

35. From Moonrocks, it has been determined that the highlands (light grey regions) are 4 to 4.5 billion years old and the maria (the darker regions) are about 3.5 billion years old.

36. Tight age around 3.5 Gyrs
Ages between 4 and 4.5 Gyrs

37. Highlands
Maria

38. The highlands are smothered in craters. Saturated!!!
The mare are moderately cratered.

39. 200 Myrs
3.5 Gyrs
4-4.5 Gyrs

40. Surface age based on cratering
1) Smothered with craters; the surface is billion years old. (e.g. Lunar Highlands)
2) medium (-heavy?) cratered; 3.5 billion years old. (e.g. Lunar maria)
3) lightly cratered; ~ million years old. (e.g. Earth's surface)
4) no craters; <few million years old.
This is the yardstick against which all surface ages will be measured.

41. Assume the same scale for all picturesB
Assume the same scale for all pictures D C

42. Assume the same scale for all picturesB
million:
Earth-like
2-4 billion: Maria-like
Assume the same scale for all pictures
Few million:
no craters D C
4-4.5 billion: saturated