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UCLA Meteorite Gallery Lecture Series

Title: Clocks in Rocks: How to date a solar system

Lecturer: Dr. Sara Russell; Natural History Museum, London

Our solar system was born over four and a half billion years ago, from a cloud of dust and gas called the protoplanetary disk. Examples of the first solids to be formed - calcium-aluminium-rich inclusions (CAIs) and chondrules -have survived in some meteorite samples to learn about these ancient times. In particular, we can determine how old these components are using lead isotopes, which places constraints on the formation time of our Sun and planets. Finer details can be provided by the isotope 26Al, which is a natural clock because it is radioactive and its abundance declines by half every 3/4 of a million years. By looking at how much of this isotope was present in each object when it formed we can therefore tell how old it is. However, this chronometer depends on knowing how much 26Al originally existed in the disk and how it was distributed. If we can work these details out, then we can use these data to determine the length of time it took to make CAIs and chondrules, and from this we can work out how long the dusty disk took to start to form planets.

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