AS 91412 annotated exemplars

This annotated exemplar is intended for teacher use only. Annotated exemplars are extracts of student evidence, with commentary, that explain key parts of a standard. These help teachers make assessment judgements at the grade boundaries.

TKI Earth and Space Science assessment resources (external link)

Download all these exemplars and commentary [PDF, 306 KB]

For Excellence, the student needs to comprehensively investigate the evidence related to dating geological event(s).

This involves:

• justifying how a range of key evidence contributes to the understanding of the dating of the geological event(s)
• explaining how the cross-correlation of the evidence contributes to the understanding of the dating of geological event(s).

This student has conducted a comprehensive investigation by dating the Park Volcanics group in south-east Southland. Relevant dating techniques have been investigated, justifying those selected (1). A final age has been cross-correlated using 3 techniques (2). 

For a more secure Excellence, the student could explain comprehensively how the Rb-Sr dating technique works, its half-life and decay method and why it was selected for cross-correlation. ⁸⁷Rb decays to ⁸⁷Sr with a half-life of 48.8 billion years and is accurate as long as no metamorphism occurs. This is true in the Park Volcanics.

For Merit, the student needs to investigate in depth the evidence related to dating geological event(s).

This involves explaining, in detail, how a range of key evidence contributes to the understanding of the dating of geological event(s).

This student has conducted an in-depth investigation by dating the Park Volcanics group in south-east Southland. Dating techniques have been investigated in depth, and the key techniques have been selected and justified (1)    

To reach Excellence, the student could explain in depth a cross-correlation using the ⁴⁰Ar-³⁹Ar and ⁴⁰K-⁴⁰Ar methods to narrow down the final agreed age of 199.6ma. The student could also explain how these two methods are most accurate because Argon accumulates after the final crystallisation of igneous rocks. The significance of the small error range for ⁴⁰Ar*-³⁹Ar could be discussed.

For Merit, the student needs to investigate in depth the evidence related to dating geological event(s).

This involves explaining, in detail, how a range of key evidence contributes to the understanding of the dating of geological event(s).

This student has conducted an in-depth investigation by dating the Park Volcanics group in south-east Southland. One dating technique has been investigated in depth and two others explained (1).

For a more secure Merit, the student could explain in depth how the Rb-Sr and ⁴⁰K-⁴⁰Ar methods operate to give a more accurate age of the Park Volcanics, and explain that ⁴⁰Ar-³⁹Ar has been used as a reliable technique but geological dating requires cross-correlation with other techniques to get a more accurate age.

For Achieved, the student needs to investigate the evidence related to dating geological event(s).

This involves:

• explaining geological events
• explaining a range of evidence related to dating geological event(s).

This student has conducted an investigation for dating the Park Volcanics group in south-east Southland. The event has been explained and linked to a back arc system (1). One dating technique has been investigated and two others mentioned (2).

To reach Merit, the student could explain how the ⁴⁰K-⁴⁰Ar and Rb-Sr methods give a relevant final age of 199.6ma, and explain that dating of rocks requires a number of techniques to be used to give a more accurate result of the final age.

For Achieved, the student needs to investigate the evidence related to dating geological event(s).

This involves:

• explaining geological events
• explaining a range of evidence related to dating geological event(s).

This student has conducted an investigation for dating the Park Volcanics group in south-east Southland. The event has been explained and linked to the volcanic rocks erupted (1). One dating technique has been explained and one other relevant technique mentioned (2). 

For a more secure Achieved the student could explain how the ⁴⁰K-⁴⁰Ar and Rb-Sr methods give a relevant final age of 199.6ma.

For Achieved, the student needs to investigate the evidence related to dating geological event(s).

This involves:

• explaining geological events
• explaining a range of evidence related to dating geological event(s).

This student has conducted an investigation for dating the Park Volcanics group in south-east Southland. The event has been explained and rocks identified (1). Two dating techniques have been explained as well as how ¹⁴C is used for dating (2).

To reach Achieved, the student could explain two relevant dating techniques and explain how relevant techniques must involve isotopes with long half-lives (greater than 1 million years) to give an age of 200ma.