Howardites

The answer sheet for the worksheet Chondrites: the oldest rocks. 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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Start here: Explorer · Ages 10 and upAnswer sheet for teachers

Answers: Chondrites: the oldest rocks

  1. D: CAIsCAIs are irregular white or pinkish patches; chondrules are round, and metal and troilite are metallic.
  2. A: They are gases that solid rock did not keepThe Sun is mostly hydrogen and helium gas, which rocks did not hold on to, so only the other elements are compared.
  3. B: From a fraction of a millimetre to a few millimetresChondrules are usually between a fraction of a millimetre and a few millimetres across.
  4. D: An iron sulphide mineralTroilite is an iron sulphide mineral scattered, with metal grains, through many chondrites.
  5. A: Very close, if gases like hydrogen and helium are left outLeaving out gases such as hydrogen and helium, chondrite chemistry is very close to the Sun's.
  6. False: the right answer is Sometimes more than half the rockIn many chondrites chondrules make up a large share, sometimes more than half.
  7. False: the right answer is They condense at the highest temperatures as the gas coolsAs a hot gas of solar composition cools, minerals rich in calcium and aluminium condense first.
  8. It formed in another star before the Solar System existed (accept any answer with the same meaning)Some matrix holds rare grains of stardust made in other stars, older than the Sun itself.
  9. About 1 million years after the CAIs formed (accept any answer with the same meaning)Time zero is the age of the CAIs, about 4,567 million years ago, so later events are timed from it.
  10. The cake around the fruit (accept any answer with the same meaning)The cake surrounds everything, just as fine-grained matrix surrounds the chondrules and CAIs.

Task

Answers will vary. The task comes from the lesson: Look closely at a slice of fruit cake or a chocolate chip cookie. Draw it and label the parts: the round fruits or chips are like chondrules, the odd-shaped pieces are like CAIs, and the cake around them is like matrix.

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

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