Howardites

The answer sheet for the worksheet Early Solar System chronology. 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: Early Solar System chronology

  1. A: About 0.72 million yearsHalf the initial abundance means one half-life of aluminium-26 had passed, about 0.72 million years.
  2. B: They are the oldest dated Solar System solidsCAIs give the oldest age, about 4,567.3 million years, defining the start of the Solar System.
  3. B: Hafnium-182With a half-life of about 8.9 million years, hafnium-182 remains measurable over longer spans.
  4. D: Far more aluminium-26 remained at 1 MyrAluminium-26 decays quickly, so late accretion captured too little of it to melt the body.
  5. B: They were only warmed, altered or metamorphosedWith less aluminium-26, later bodies were only metamorphosed or altered by water, not melted.
  6. True (Some chondrules began forming very early)Overlapping ages suggest chondrule formation started very soon after CAIs, if not alongside them.
  7. True (The initial abundance at closure)The slope gives the initial radionuclide abundance, which is compared with the CAI value.
  8. About 1 to 3 million years after CAIs (accept any answer with the same meaning)Tungsten isotopes imply metal segregation within roughly the first one to three million years.
  9. About 6 per cent (accept any answer with the same meaning)3 million years is about 4.2 half-lives of 0.72 million years, and 2 to the power −4.2 is about 0.06.
  10. About 2 to 4 million years after CAIs (accept any answer with the same meaning)Most chondrite parent bodies accreted roughly two to four million years after CAIs.

Task

Answers will vary. The task comes from the lesson: Draw a timeline from 0 to 10 million years after CAIs. Place CAIs, chondrules, iron meteorite core formation, chondrite parent body accretion and angrite crystallisation in their approximate positions.

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