Choose the best methods for finding the absolute dates of different rock layers.

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Rights: University of Waikato. All rights reserved. Published 24 June 2016

This interactive asks you to choose the best absolute dating method for each layer of rock in a cliff. Your choice will depend on the material present in each rock.

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Transcript

Welcome

We have found this cliff and collected samples from the layers of sedimentary rocks. We know the oldest rocks are at the bottom and the youngest are at the top, but we want some actual dates.

You can help us choose the best absolute dating method for each rock.

Instructions

We’ve numbered the rock layers 1–6. Layer 1 is the oldest.

Drag and drop the rock sample from each layer onto the dating method you think will tell us its age.

To learn more about the dating methods, select the image from the lab.

Name: Radiocarbon dating
Material used: Organic remains such as wood and seeds
Age range: Younger than 60,000 years ago
How it works: Measures the amount of radioactive carbon-14 in the organic remains of living things

Name: Fission track dating
Material used: Volcanic glass, zircon and other crystals
Age range: 10,000 to 500 million years ago
How it works: Measures radioactivity by counting tracks left in crystals by decaying uranium atoms

Name: Optically stimulated luminescence (OSL) 
Material used: Wind-blown sediment with lots of quartz or feldspar mineral grains
Age range: Younger than 100,000 years ago
How it works: Measures radiation that the mineral receives after it has been buried away from light

Name: Fossil correlation
Material used: Fossils
Age range: All ages
How it works: Fossils found in an undated rock are matched to similar fossils found in rocks that have been dated in other places

Layer 1: Mudstone – sediments laid down in deep water. Fossils include the belemnite Belemnopsis aucklandica.
Which dating method is best for rocks with fossils in?

Layer 2: Mudstone – sediments laid down in deep water. Fossils includeAstraea (circular-saw shell).
Which dating method is best for rocks with fossils in?

Layer 3: A thin layer of tephra – a rock made of the ash from a volcanic eruption.
Which dating method is best for volcanic ash containing crystals of zircon?

Layer 4: Mudstone – sediments laid down in deep water. Fossils include oysters and a large scallop.
Which dating method is best for rocks with fossils in?

Layer 5: Loess – a rock made from very fine wind-blown dust. Contains feldspar crystals.
Which dating method is best for rocks with feldspar crystals buried in dust?

Layer 6: The remains of old dunes formed from wind-blown sand. Pieces of wood were found near the bottom of this young layer.
Which dating method is best for organic material?