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The answer sheet for the worksheet Petrologic types: from wet to hot. Each answer comes with the reason, so it can be used to mark or to go over the questions with the class.

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Answers: Petrologic types: from wet to hot

  1. D: Stardust made around other stars before the SunPresolar grains are tiny crystals that formed around other stars before the Sun existed.
  2. D: It is among the least altered chondritesType 3 marks the pristine middle of the scale: little changed by either water or heat.
  3. A: Their grains never swapped atoms, so they differOlivine and pyroxene grains in type 3 vary widely from grain to grain because they have not swapped atoms with each other.
  4. B: Ice in the parent body melted as it warmedEarly parent bodies contained ice; as they warmed, it melted and the water reacted with the rock.
  5. D: The CI1Type 1 means more water alteration than type 2, so the CI1 is the more altered of the two.
  6. False: the right answer is It is a debated class for near-melted chondritesSome scientists use type 7 for chondrites heated almost to melting, but the category is debated.
  7. False: the right answer is They respond to very mild heatingThese measurements are sensitive to very gentle heating, which is what separates one type 3 subtype from the next.
  8. Cooling rates measured from minerals (accept any answer with the same meaning)Cooling rates measured from minerals in the different types broadly fit a layered, onion-like parent body.
  9. Several hundred degrees Celsius (accept any answer with the same meaning)Types 4 to 6 were typically heated to several hundred degrees Celsius, below melting.
  10. Glass that has not crystallised (accept any answer with the same meaning)Type 3 chondrules have sharp outlines and many still contain glass, because they were barely heated.

Task

Answers will vary. The task comes from the lesson: Draw a horizontal line labelled 1 to 6. Mark type 3 in the middle as pristine, write water above types 1 and 2, and heat above types 4 to 6. Add examples from this course to the line as you meet them.

Look for work that uses the key words correctly and gives a reason for each point.

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