Howardites

A printable worksheet for the lesson Early Solar System chronology (Start here: Expert). It prints on A4 without the website around it. The answers are on a separate sheet for the teacher.

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Early Solar System chronology

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Key words

Isotope
One of two or more forms of the same chemical element whose atoms have different numbers of neutrons, and so different masses.
Chondrite
A chondrite is a stony meteorite full of tiny round grains called chondrules, and almost unchanged since the Solar System formed.
Chondrule
A chondrule is a tiny round grain, often smaller than a grain of rice, that formed as a melted droplet in space before the planets existed.
Aluminium-26
A short-lived radioactive isotope of aluminium, now extinct in early solar-system materials, that dated and heated the first planetesimals.
Angrite
A rare, extremely old basaltic achondrite rich in calcium and aluminium and strongly depleted in volatile elements.
Iron meteorite
An iron meteorite is made mostly of iron and nickel metal.

Choose the right answer

Circle the letter of the right answer.

  1. A chondrule's initial 26Al/27Al is half the CAI value. Roughly how long after CAIs did it close?
    • AAbout 0.72 million years
    • BAbout 2.6 million years
    • CAbout 1.44 million years
    • DAbout 0.36 million years
  2. Why are CAIs from CV chondrites used as time zero?
    • AThey were made deep inside the young Sun itself
    • BThey are the oldest dated Solar System solids
    • CThey contain no radioactive isotopes of any kind
    • DThey are the most common objects in all meteorites
  3. Which short-lived system best suits events spread over 10 to 20 million years?
    • AAluminium-26
    • BHafnium-182
    • CManganese-53
    • DIron-60
  4. Why could a body that accreted at 1 million years melt, but one at 3 million years could not?
    • ALater bodies all accreted out beyond Neptune
    • BThe young Sun was much hotter at 1 Myr
    • CBodies that accreted later were always smaller
    • DFar more aluminium-26 remained at 1 Myr
  5. What happened to bodies that accreted later than about 1.5 million years after CAIs?
    • AThey broke apart before any heating could begin
    • BThey were only warmed, altered or metamorphosed
    • CThey stayed frozen and never warmed at all
    • DThey melted fully and formed metal cores

True or false?

Is the answer given right? Tick True or False.

  1. The oldest chondrules give lead-lead ages that overlap with CAIs. What does this suggest?

    Answer given: Some chondrules began forming very early TrueFalse

  2. What does the slope of a short-lived radionuclide isochron give?

    Answer given: The initial abundance at closure TrueFalse

Write your answer

Answer in a word or a short sentence.

  1. When did metal segregate in the parent bodies of magmatic iron meteorites?
  2. About what fraction of the initial aluminium-26 remained 3 million years after CAIs?
  3. When did most chondrite parent bodies accrete?

Task

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.

Howardites · free to copy for use in your classroom · answers are on the separate teacher's answer sheet