Absolute dating methods give rocks an actual date or date range in numbers of years. This interactive explores four different methods used in absolute dating.
Scientists often need to know the actual dates of geological events so they can study landscape and environmental change. Absolute dating methods provide this type of information. Scientists have a variety of absolute dating methods to choose from, depending on the materials available in their rocks. This interactive explores four different methods used in absolute dating.
To use this interactive, move your mouse or finger over any of the labelled boxes and select to obtain more information.
When an organism dies, it no longer absorbs C-14. The C-14 it does contain in its tissues starts to decay at a constant rate.
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
Image: Pollen grains micrograph, GNS Science
Optically stimulated luminescence (OSL)
Before being buried in sediment, crystals exposed to sunlight lose previously stored energy from radiation. This sets the geological ‘clock’ to zero.
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
Image: Dr Uwe Rieser and Ms Ningsheng Wang, Luminescence Dating Laboratory, Victoria University of Wellington
Fission track dating
When uranium decays, subatomic particles split away. The particles leave tiny tracks in the crystal structure of minerals such as zircon and apatite.
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
Image: Fission tracks in the mineral apatite viewed through a microscope, Geotrack International Pty Limited, Melbourne
Fossils are the remains of once-living organisms preserved in rocks. Fossils include shells and bones.
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
Image: Ammonite fossil, The University of Waikato Te Whare Wānanga o Waikato