Howardites

A printable worksheet for the lesson Oxygen isotopes: the fingerprint of origin (Start here: Expert). It prints on A4 without the website around it. The answers are on a separate sheet for the teacher.

Answer sheet for teachersBack to the lessonAll worksheets

Start here: Expert · AdvancedHowardites worksheet

Oxygen isotopes: the fingerprint of origin

Name:Class:Date:

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.
Classification
Classification is the process of identifying exactly what kind of meteorite a specimen is and giving it an official type and group.
Crystallisation
Crystallisation is the growth of crystals from a melt, a gas or a solution, or within a solid as it is heated.
Chondrite
A chondrite is a stony meteorite full of tiny round grains called chondrules, and almost unchanged since the Solar System formed.
CCAM line
The CCAM line is a line on oxygen isotope plots defined by anhydrous minerals of carbonaceous chondrites, with a slope near 1.
Parent body
The asteroid, moon or planet that a meteorite was originally part of before it was knocked off into space.

Choose the right answer

Circle the letter of the right answer.

  1. How is oxygen commonly extracted from silicates for isotope analysis?
    • AHeating the whole stone in a furnace
    • BDissolving a kilogram of rock in water
    • CLaser fluorination of about a milligram
    • DGrinding the sample under a vacuum pump
  2. A meteorite has Δ17O of almost exactly zero. Which group could it belong to?
    • AHED meteorites
    • BAubrites
    • CLL chondrites
    • DR chondrites
  3. What is one leading explanation for the mass-independent oxygen signatures of the early Solar System?
    • ASelf-shielding of CO by ultraviolet light
    • BShock melting during asteroid collisions
    • CWater alteration on carbonaceous parent bodies
    • DEvaporation of chondrules in the nebula
  4. Why was the Sun's oxygen isotope composition uncertain for decades?
    • AIts oxygen composition changes too quickly to measure
    • BThe Sun contains almost no oxygen at all to measure
    • CNo meteorite has ever been found to contain solar gas
    • DThe photosphere cannot be measured precisely enough
  5. Ureilites vary in Δ17O from sample to sample along the CCAM line. What does this suggest?
    • ATheir parent body was never fully homogenised
    • BThey share the HED parent body
    • CThey come from Earth's upper mantle
    • DTheir oxygen was reset by terrestrial weathering

True or false?

Is the answer given right? Tick True or False.

  1. In self-shielding models, how did planetary dust acquire its heavier oxygen?

    Answer given: By exchange with water ice rich in 17O and 18O TrueFalse

  2. Why do mass-dependent processes change δ17O by about 0.52 times the change in δ18O?

    Answer given: 17O differs from 16O by one mass unit, 18O by two TrueFalse

Write your answer

Answer in a word or a short sentence.

  1. What did the Genesis mission collect between 2001 and 2004?
  2. Why is the Moon's position on the terrestrial fractionation line a strong constraint on its origin?
  3. A sample has δ17O of +3.0 and δ18O of +5.0 per mil. What is its approximate Δ17O?

Task

Sketch a three-isotope plot with δ18O on the horizontal axis and δ17O on the vertical. Draw the TFL with slope 0.52 and the CCAM line with slope near 1. Mark approximate positions for H, L, LL, HED, Martian and enstatite meteorites.

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